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POTATOES IN RELATION TO MAGNESIUM FERTILIZATION, SPROUTING, MICROWAVE BAKING AND PRODUCT DEVELOPMENT

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8210803
Klein, Lisa Beth
POTATOES IN RELATION TO MAGNESIUM FERTILIZATION, SPROUTING,
MICROWAVE BAKING AND PRODUCT DEVELOPMENT
Ph.D.
Cornell University
University
Microfilm s
International
1982
300 N. Zeeb Road, Ann Arbor, M I 48106
PLEASE NOTE:
The negative m icro film copy of this
dissertation was prepared and inspected by the
school granting the degree. We are using this
film without further inspection or change. If
there are any questions about the film content,
please w rite d irectly to the school.
U N IVER SITY M ICROFILM S
POTATOES IN RELATION TO MAGNESIUM FERTILIZATION, SPROUTING,
MICROWAVE BAKING AND PRODUCT DEVELOPMENT
A Thesis
Presented to the Faculty o f the Graduate School
of Cornell U n i v e r s i t y
in P a r t i a l
F u l f i l l m e n t f o r the Degree of
Doctor of Philosophy
Lisa Beth Klein
January, 1982
BIOGRAPHICAL SKETCH
The author was born in New York C i t y on A p r i l
permanent residence is Manhattan.
Nutritional
26 , 1955.
Her
She received a B.S. degree in
Sciences in May, 1978 and an M.S. degree in Food Science in
January, 1980, both from C o r n e l l .
She began doctoral
studies in the
Department of Food Science immediately a f t e r r e c e i v i n g her masters
degree.
ii
DEDICATION
To
My Family
and Very Special Friend
ACKNOWLEDGEMENTS
The author wishes to express sincere a p p re ci a ti on to Dr. Nell
Mondy, the Chairperson of her Special Committee, f o r her support,
encouragement and guidance during t h i s study.
She also expresses
g r a t i t u d e to Dr. Max Brunk and Dr. Chris Wilkinson, the o th er members of
her Special Committee, f o r t h e i r support and assistance.
The author also acknowledges the l a b o r a t o r i e s of Drs. Kwong,
Morrison and Kowsikowski f o r help with the m in e r a l, amino acid and
extr usio n procedures.
TABLE OF CONTENTS
Page
INTRODUCTION .................................................................................................................
1
GENERAL EXPERIMENTAL PROCEDURES
....................................................................
4
...................................................................................................
4
Ascorbic Acid Determination
......................................................
Crude L i p i d Determination
...........................................................
Phospholipid F r a c t i o n a t io n ...........................................................
Fa tty Acid A n a l y s i s ........................................................................
Determination o f Phenols ...............................................................
D i s c o lo r a t i o n Determination
......................................................
Total Nitrogen Determination ......................................................
Non-Protein Nitrogen ........................................................................
Percent Pr ot ei n
.................................................................................
E xt ra ct io n and Q u a n t it a t io n o f Free Amino Acids
. . .
Total Amino A c i d s .............................................................................
Mineral Analysis .................................................................................
Sampling Procedure .............................................................................
S t a t i s t i c a l Analyses ........................................................................
4
5
6
7
8
9
10
11
11
11
12
12
13
13
In tr o d u c t io n
MAGNESIUM STUDY
........................................................................................................
14
...................................................................................................
14
Y i e l d ........................................................................................................
D i sc o lo r at io n and Phenolic Content .........................................
L i p i d s ........................................................................................................
N i t r o g e n ...................................................................................................
M i n e r a l s ...................................................................................................
F i r m n e s s ...................................................................................................
14
15
16
17
18
19
M a t e r i a l s and Methods .................................................................................
Results and Discussion
...............................................................
20
21
Y i e l d ........................................................................................................
Di s c o lo r a t i o n
......................................................................................
P h e n o l s ...................................................................................................
L i p id C o m p o s i t i o n .............................................................................
Total N i t r o g e n .....................................................................................
Non-Protein Nitrogen and Protein .............................................
Amino A c i d s ..........................................................................................
M i n e r a l s ...................................................................................................
F i r m n e s s ...................................................................................................
21
21
21
26
29
29
35
38
41
Summary................................................................................................................
C o n c l u s i o n ........................................................................................................
41
43
In tr o d u c t io n
v
Page
SPROUTING STUDY
I n t r o d u c t io n
........................................................................................................
45
...................................................................................................
45
Sprouting and Potato Physiology
.............................................
46
M a t e r i a l s and Methods .................................................................................
Results and Discussion
.............................................................................
47
48
Total Ni trogen, Non-Protein Nitrogen and Protein
Content of T u b e r s ........................................................................
Tota l Nit ro gen , Non-Protein Nitrogen and Prot ei n
Content of S p r o u t s ........................................................................
..................
E f f e c t o f Li ght on Nitrogenous Constituents
Total Amino Acid Content o f T u b e r s .........................................
Total Amino Acid Content o f S p r o u t s .....................................
Mineral Composition
........................................................................
48
48
56
56
60
62
Summary.................................................................................................................
C o n c l u s i o n ........................................................................................................
65
66
SPROUT INHIBITOR STUDY ..........................................................................................
67
I n t r o d u c t io n
...................................................................................................
67
Ma leic Hydrazide .................................................................................
C I P C ............................................................................................................
67
72
M a t e r i a l s and Methods— Male ic H y d r a z i d e ...........................................
73
Tuber T i s s u e ......................
Sprout and Bud T i s s u e ....................................................................
73
74
Results and Discussion
.............................................................................
75
Total N i t r o g e n ......................................................................................
Non-Protein Nitrogen ........................................................................
P r o t e i n ...................................................................................................
Mineral Content o f Tuber Tissues ................................................
Mineral Content o f Apical Bud and Sprouts
..........................
75
75
79
79
79
M a t e r i a l s and Methods— C I P C ...................................................................
90
Tuber T i s s u e ..........................................................................................
Bud T i s s u e ...............................................................................................
90
90
Results and Discussion
.............................................................................
91
Nitrogenous Constituents....... ...........................................................
Mineral Content
.................................................................................
91
95
vi
Page
Summary.................................................................................................................
C o n c l u s i o n ........................................................................................................
COOKING STUDY
95
95
............................................................................................................
99
In tr o d u c t io n
...................................................................................................
M a t e r i a l s and Methods .................................................................................
Results and Discussion
..........................................................................
99
102
103
Tot al N i t r o g e n ......................................................................................
Non-Protein Nitrogen ........................................................................
Pro te in and Amino Acids
...............................................................
Mineral Contents .................................................................................
103
103
106
Ill
Summary.................................................................................................................
C o n c l u s i o n ........................................................................................................
114
114
POTATO/WHEAT SNACK ...................................................................................................
116
In tr o d u c t io n
...................................................................................................
M a te r i a l s and Methods .................................................................................
116
118
I n g r e d i e n t s ..........................................................................................
Product Formulations ........................................................................
Process Conditions..... ..........................................................................
Moisture Content .................................................................................
Oil C o n t e n t ..........................................................................................
Te x tu ra l Determinations
...............................................................
Sensory Evaluation..... ..........................................................................
S t a t i s t i c a l Analysis ........................................................................
118
119
119
119
119
121
122
122
..........................................................................
122
St a n d a r d iz a ti o n of Formulas
.........................................................
E x t r u s i o n ...............................................................................................
F r y i n g ........................................................................................................
Sensory Evaluation
..........................................................................
O b je ct iv e Tex tural Determinations
............................................
122
124
124
126
134
Summary.................................................................................................................
139
Results and Discussion
APPENDIX TABLES
........................................................................................................
141
REFERENCES.....................................................................................................................
151
vi i
LIST OF TABLES
The e f f e c t o f MgSO, f e r t i l i z a t i o n on the f r e e amino acid
content (mg/g D.W.J o f Katahdin potato tubers (Year 1) . . .
36
The e f f e c t o f MgSO* f e r t i l i z a t i o n on the t o t a l
(hydrolyzed) amino acid content (mg/g D.W.) o f Katahdin
potato tubers (Year 1)
.............................................................................
37
The e f f e c t o f McjSO, f e r t i l i z a t i o n on the macromineral
content (% D.W.) o f Katahdin potato tubers
................................
39
The e f f e c t o f MgSO, f e r t i l i z a t i o n on the micromineral
content (ppm) o f Katahdin potato tubers .........................................
40
The e f f e c t o f germination in the l i g h t and dark on the
t o t a l n i t r o g e n , non -protein nitrogen and p r o t e i n contents
o f co r t e x , p i t h and sprout tissues o f NY 61 potatoes
. . .
49
The e f f e c t o f germination in the l i g h t and dark on the
t o t a l n i tr o g e n , non -protein nitrog en and p r o t e i n contents
o f c o r t e x , p i t h and sprout tissues o f Katahdin potatoes . .
50
The e f f e c t o f germination in the l i g h t and dark on the
t o t a l n i t r o g e n , non -protein nitrog en and pr o t e i n contents
o f c o r t ex , p i t h and sprout tiss ues o f Kennebec potatoes . .
51
The e f f e c t o f germination in the l i g h t and dark on the
t o t a l (hydrolyzed) amino acid contents (mg/g D.W.) of
.................................................................................
potato cortex t i s s u e
59
The e f f e c t o f germination in the l i g h t and dark on the
t o t a l (hydrolyzed) amino acid contents (mg/g D.W.) of
potato sprouts
...............................................................................................
61
The e f f e c t o f germination in the l i g h t and dark on the
macromineral composition { % D.W.) o f c o r t e x , p i th and
sprout tissues o f potatoes
....................................................................
63
The e f f e c t o f germination in the l i g h t and dark on the
micromineral composition (ppm) o f c o r t e x , p i t h and
sprout tissues o f potatoes
....................................................................
64
The e f f e c t o f MH on the macromineral composition of cortex
and p i t h potato t is s u e (MH at 0 and 3 l b s / a c r e ) .......................
83
The e f f e c t o f MH on the micromineral composition of cortex
and p i th potato t is s u e (MH a t 0 and 3 l b s / a c r e ) .......................
84
vi i i
Page
The e f f e c t of MH on the macromineral and micromineral
composition of Katahdin potato cortex t is s u e (MH a t 0
and 9 l b s / a c r e ) ..........................................................................................
85
The e f f e c t of MH on the macromineral composition o f
potato tub er apical and sprout t is s ue (MH a t 0 and 3 l b s /
a c r e .................................................................................................................
86
The e f f e c t o f MH on the micromineral composition of
potato tuber apical bud and sprout t is s u e (MH a t 0 and
3 l b s / a c r e ) ...................................................................................................
87
The e f f e c t of CIPC on the macromineral composition of
c o r t e x , p i t h and api cal bud t is s u e o f Katahdin potato
tubers
............................................................................................................
96
The e f f e c t of CIPC on the micromineral composition of
c o r t e x , p i t h and api cal bud t is s u e of Katahdin potato
tubers
............................................................................................................
97
I n fl u e n c e of baking method on the t o t a l amino acid
contents o f potatoes
.............................................................................
108
In f l u e n c e of baking method on the f r e e amino acid
contents of potatoes
.............................................................................
109
In f l u e n c e of baking method on the macromineral content
(% D.W.) of p o t a t o e s .............................................................................
112
In fl u e n c e of baking method on the micromineral content
(ppm) of potatoes ......................................................................................
113
The moisture content o f the inte rm ed iat e product, and the
moisture and f a t contents of the f t i e d product cooked at
190-195°C .......................................................................................................
127
Sensory ev a lu a tio n o f appearance, t e x t u r e , f l a v o r and
preference of th re e for mu lati ons of the f r i e d product
(N = 24)
.......................................................................................................
128
Sensory ev a lu a tio n o f appearance, t e x t u r e , f l a v o r and
preference of the t hr ee fo rmulations of the dried
product (N = 12)
......................................................................................
133
T ex tu ra l data f o r the d r ie d products using the Instron
Universal Testing Machine w ith a ch ar t speed o f 5 in /m i n ,
a cross head speed of 0 . 5 in/min and a r e l a x a t i o n period
of 1 min .......................................................................................................
138
ix
LIST OF ILLUSTRATIONS
Figure
1.1
1.2.
1.3.
1.4.
1.5.
1.6.
1.7.
1.8.
1.9.
1. 10 .
1. 1 1 .
1. 12 .
2.1.
2.2.
Page
E f f e c t o f magnesium f e r t i l i z a t i o n on the y i e l d o f
Katahdin potatoes ...............................................................................................
22
E f f e c t of magnesium f e r t i l i z a t i o n on the d i s c o l o r a t i o n of
cortex t is s u e from Katahdin potatoes.
Reflectance value
(Rd) decreases as blackening increases
.............................................
23
E f f e c t o f magnesium on the d i s c o l o r a t i o n o f cortex t iss ue
..............................
from Katahdin potatoes assessed s u b j e c t i v e l y
24
E f f e c t o f magnesium f e r t i l i z a t i o n on the phenolic content
o f cortex t is s u e from Katahdin potatoes .............................................
25
E f f e c t of magnesium f e r t i l i z a t i o n on the crude l i p i d content
o f cortex tiss ue from Katahdin potatoes .............................................
27
E f f e c t o f magnesium f e r t i l i z a t i o n on the phospholipid
content o f cortex t i s s u e from Katahdin potatoes ...........................
28
E f f e c t of magnesium f e r t i l i z a t i o n on the f a t t y acid
composition of cortex t i s s u e from Katahdin potatoes
grown during Year 1 ..........................................................................................
30
E f f e c t o f magnesium f e r t i l i z a t i o n on the f a t t y acid
composition of cortex t i s s u e from Katahdin potatoes
grown during Year 2 ..........................................................................................
31
E f f e c t o f MgSCL a p p l i c a t i o n on the t o t a l ni tro ge n content
o f Katahdin potato tubers .............................................................................
32
E f f e c t of MgSO. a p p l i c a t i o n on the non-p ro te in nitrogen
content o f Katahdin potato tubers ...........................................................
33
E f f e c t o f MgSCL a p p l i c a t i o n on the p r o t e i n content of
Katahdin potatd tubers
.................................................................................
34
E f f e c t of MgSCL a p p l i c a t i o n on the actual
o f Katahdin potato tubers (Year 3)
42
deformation (mm)
E f f e c t o f germination in the l i g h t and dark on the p r o t e i n no n- protein nitrogen r a t i o s o f potato cortex t is s u e .....................
52
E f f e c t of germination in the l i g h t and dark on the p r o t e i n no n- protein nitrogen r a t i o s o f potato p i t h t i s s u e .......................
53
x
Page
2.3.
2.4.
2.5.
2.6.
3.1.
3.2.
3.3.
3.4.
3.5.
3.6.
3.7.
3.8.
3.9.
E f f e c t o f germination in the dark on the t o t a l nitrogen
content o f potato c o r t e x , p i t h and sprout tiss ues .......................
54
E f f e c t o f germination in the dark on the non-p ro te in
ni tro ge n content o f potato c o r t e x , p i t h and sprout tissues
.
55
E f f e c t of germination in the dark on the p r o t e i n content
o f potato co rt ex , p i t h and sprout t is s u e
.........................................
57
E f f e c t o f germination in the l i g h t and dark on the p r o t e i n no n- pr ot ei n nitrogen r a t i o s o f potato sprouts ................................
58
Effect of
0 and 3 l b s / a c r e MH on the t o t a l ni tro ge n content
o f cortex and p i th tis s u e s from Katahdin potato tubers grown
on L. I . , and Katahdin and Kennebec tubers grown a t
Itha ca (Year 1 ) ...................................................................................................
76
E f f e c t o f 0 , 3, 6 and 9 l b s / a c r e MH on the t o t a l nitrogen
content o f cortex t i s s u e from Katahdin potato tubers
grown on L. I . (Year 2 ) .................................................................................
77
Effect of
0 and 3 l b s / a c r e MH on the no n- pr ot ei n nitrogen
content o f cortex and p i t h tissues from Katahdin potato tubers
grown on L. I . , and Katahdin and Kennebec tubers grown at
Ithac a (Year 1 ) ...................................................................................................
78
E f f e c t o f 0 , 3, 6 and 9 l b s / a c r e MH on the non-protein
nitrog en content o f cort ex t is s u e from Katahdin potato
tubers grown on L. I . (Year 2 ) ...............................................................
80
E f f e c t o f 0 and 3 l b s / a c r e MH on the p r o t e i n content of
cort ex and pi th tis s ue s from Katahdin potato tubers grown
on L. I . , and Katahdin and Kennebec tubers grown a t
Itha ca (Year 1 ) ...................................................................................................
81
E f f e c t o f 0 , 3, 6 and 9 l b s / a c r e MH on the p r o t e i n content
of cortex tissu e from Katahdin potato tubers grown on
L. I . (Year 2 ) .................................................................................................\
.
82
E f f e c t of MH on the length o f sprouts from the Kennebec
and Katahdin v a r i e t i e s
. . . . .
...........................................................
89
E f f e c t of CIPC on the t o t a l nitrogen content o f potato
cortex and pi th t i s s u e s .................................................................................
92
E f f e c t o f CIPC on the non -protein nitrogen content of
potato cortex and p i t h t i s s u e s ...............................................................
93
xi
Page
3. 1 0 .
E f f e c t o f CIPC on the p r o t e i n content of potato cortex
and p i t h t i s s u e s ...............................................................................................
94
4.1.
E f f e c t of baking methods on the t o t a l nitrogen contents
o f co rt ex and p i t h potato t i s s u e .....................................................................104
4.2.
E f f e c t o f baking methods on the non-protein ni tro ge n
cont ent of cortex and p i t h potato t i s s u e ................................................. 105
4.3.
E f f e c t o f baking methods on the pr ot ei n content o f cortex
and p i t h potato t i s s u e .......................................................................................107
5.1.
Extruder heads and s c r e w ................................................................................... 120
5.2.
Taste Panel Score Sheet ..................................................................................
123
5.3.
Extruded product
125
5.4.
F r ie d p r o u d c t .............................................................................................................. 125
5.5.
Appearance o f the f r i e d p r o d u c t ..................................................................... 129
5.6.
Texture o f the f r i e d p r o d u c t .......................................................................... 130
5.7.
Flavo r o f the f r i e d p r o d u c t ............................................................................... 131
5.8.
Appearance o f the d r ie d p r o d u c t ......................................................................135
5.9.
Texture o f the dr ied p r o d u c t .......................................................................... 136
................................................................................................
5. 1 0 . Fl av or o f the dried p r o d u c t ............................................................................... 137
xi i
FORWARD
Potatoes are grown and consumed in large q u a n t i t i e s a l l
world, and are considered an economically important resource.
over the
Potatoes
are also a good source of n u t r i t i o n a l l y important compounds such as
m in er al s , high q u a l i t y pr o t e i n and ascorbic aci d.
The n u t r i t i v e and
sensory q u a l i t i e s o f potatoes, however, may be a f f e c t e d by c u l i t i v a t i o n ,
st orage, and processing p r a c t i c e s .
Since magnesium f e r t i l i z a t i o n ,
sprouting during st orage, the use o f chemical sprout i n h i b i t o r s , and
baking methods may a l t e r the n u t r i t i v e and o r g an ol e pt ic a c c e p t a b i l i t y o f
the f i n a l
product, changes accompanying these p r a c t i c e s were
in v e s t i g a t e d in an attempt to provide the consumer w ith the most
n u t r i t i o u s and best q u a l i t y pota to.
Present trends also i n d i c a t e increasing
foods and snack food items.
consumption o f processed
Potato chips are consumed more than any
other snack food, however, the n u t r i t i v e value o f chips is marginal.
Since the combination of potatoes w ith wheat f l o u r r e s u l t s in a product
with enhanced p r o t e i n q u a l i t y , a new potato/wheat snack was formulated
and produced in an attempt to improve the n u t r i t i v e value o f snack
foods.
INTRODUCTION
The potato o r i g i n a t e d in South America but was brought to the
United States from I re la n d in 1719.
During the nin et een th century
commercial potato production rose r a p i d l y and many new v a r i e t i e s were
o r i g i n a t e d by American p l a n t breeders.
Potatoes are now produced
commercially in every s t a t e in the United S t a t e s .
The number of farms
growing potatoes i s decreasing accompanied by l a r g e r acreages per farm.
Along w it h l a r g e r farms g r e a t e r e f f i c i e n c y in growing and harvesting
have r e s u l t e d in l a r g e r y i e l d s and b e t t e r methods o f s t o r in g potatoes
f o r l a t e r use (Sm ith, 1977).
The per c a p i t a consumption of potatoes exceeds 115 l b s , and pota­
toes contain p r a c t i c a l l y a l l
e s s e n t ia l
d i e t a r y f a c t o r s with the possible
exception of f a t and f a t - s o l u b l e n u t r i e n t s (Woodward and T a l l e y , 1953).
Potatoes are a good source o f n u t r i t i o n a l l y important compounds such as
ascorbic a c i d , s t a r c h , minerals and high q u a l i t y p r o t e i n .
I t was
reported more than 50 years ago t h a t human adults could be kept in
nitrogen balance and in good hea lth f o r as long as 5 months when fed
di et s con si s tin g s o l e l y of potatoes and a small amount of f a t .
Although the pr ot ei n content o f the potato is only about 2% on a
wet weight basis (8-10% dry w e i g h t ) , the n u t r i t i v e value o f potato
pr ot ei n is equal to or b e t t e r than soybean, and on the basis of p ro te in
q u a l i t y and crop and pr otein y i e l d s per acre, potato s a t i s f i e s the
pr ot ei n needs o f more people per acre than corn, beans, peas or wheat
(Kaldy, 1972).
Because of the high l y s i n e content o f potato p r o t e i n , i t
is also a va lu ab le supplement to cereal
1
p r ot ei ns .
On the basis of
2
percent USRDA/150 g se rv ing , the potato provides from 2-10% o f those
minerals except calcium f o r which U.S. recommended d i e t a r y allowances
have been es t a b l i s h e d ( i r o n , copper, i o d i n e , magnesium, phosphorus and
zinc)
(True e t a l . ,
1978).
L ip id s are present in r e l a t i v e l y smaller
amounts in po ta to es, but most o f the l i p i d is composed o f n u t r i t i o n a l l y
important unsaturated f a t t y ac id s.
L ip id s are also important s t r u c t u r a l
components o f membranes and may play a r o l e in determining potato tuber
s u s c e p t i b i l i t y to enzymatic d i s c o l o r a t i o n .
Enzymatic d i s c o l o r a t i o n of
potatoes is due to the re ac tio n of phenolic compounds present in tubers
wit h polyphenol oxidas e, which r e s u l t s in the formation o f brown
pigments or melanins.
Enzymatic d i s c o l o r a t i o n or black spot has been
recognized as one o f the most important tu ber defec ts in the United
States (Sawyer, 195 9).
Levels o f chemical compounds present in potatoes
may be a f f e c t e d by c u l t u r a l p r a c t i c e s , sprouting during storage and the
use of chemical sprout i n h i b i t o r s , and methods o f p re pa ra tio n and
cooking.
Chemical f e r t i l i z a t i o n
is w id e ly used.
Magnesium may be applied to
c o r r e c t magnesium d e f i c ie n c y o f s o i l s , y e t l i t t l e
is known regarding the
changes in chemical composition o f potato tubers f o l l o w i n g magnesium
application.
Sprouting markedly reduces the a c c e p t a b i l i t y of fre sh potatoes to
be used as food due to s h r i v e l i n g and weight lo s s , thus chemical sprout
i n h i b i t o r s are used in an attempt to maintain q u a l i t y and economic
return.
Maleic hydrazide (MH) and isopropyl
N-3-chlorophenyl
(CIPC) are the two most common chemicals used commercially.
the natural
carbamate
However,
breaking o f dormancy and the maintenance o f dormancy by
3
chemicals are s t i l l
poorly understood and l i t t l e
is known concerning the
e f f e c t o f sprouting and sprout i n h i b i t o r s on the chemical composition of
the tuber and sprouts.
Methods o f prep a ra tio n and cooking may a f f e c t the n u t r i t i o n a l
content of foods.
The microwave oven is used to cook f re sh potatoes,
y e t i t s e f f e c t on the nitrogen content and mineral compositon of tubers
is unknown.
The present i n v e s t i g a t i o n was undertaken to study a l t e r a t i o n s in
the chemical composition of potatoes in r e l a t i o n to magnesium
f e r t i l i z a t i o n , sprouting and the use o f sprout i n h i b i t o r s , and microwave
cooking.
A new potato-based snack food was also prepared and studied since
the author had a p a r t i c u l a r i n t e r e s t in product development, the
c o o k in g- e xt r ud er , and the f or m u la ti on o f a n u t r i t i o u s snack food.
GENERAL EXPERIMENTAL PROCEDURES
I n t r o d u c t io n
Potatoes were grown at the Cornell Homer Thompson Vegetable
Research Farm in e i t h e r F r e e v i l l e , New York, or Riverhead, Long I s l a n d ,
under the conditions s p e c if i e d f o r each study.
were stored a t 40°F (5°C) u n t i l
A f t e r harvest tubers
analyzed
Ascorbic Acid Determination
The indophenol method o f Horwitz (1970) was used to determine the
L-ascorbic acid content.
F i f t y grams o f cortex or p i t h and 150 ml o f an
ac e ti c acid-phosphoric acid mix were blended in a Waring blender f o r
three minutes, and the s l u r r y was then f i l t e r e d through u n t i l about 35
ml of f i l t r a t e was obtained.
Three 10 ml a l iq u o t s o f each e x t r a c t were
pi pet te d i n t o 50 ml Erlenmeyer f l a s k s , and t i t r a t e d to a pink col or with
indophenol dye.
T r i p l i c a t e samples o f ascorbic acid standard were run
simultaneously wit h the e x t r a c t s , w h il e the blank was prepared using
only glass d i s t i l l e d water and the a c e t i c acid-phosphoric acid mix.
A
corrected volume f o r the standard was c a lc u la t ed by sub tra ct in g the
average blank from the average standard t i t r a t i o n volumes.
The dye
strength was c a l c u l a t e d by d i v i d i n g the ascorbic acid standard by the
average corrected volume of dye.
Conversion to q u a n t i t y of ascorbic
acid was made from t i t r a t i o n values f o r the e x t r a c t s and was expressed
as mg/100 gm fre sh tissu e weight.
The acetic-phosphoric acid mix ture was prepared by adding 80 ml
glacial
a c e t i c acid and 30.0 g metaphosphoric acid to a 1000 ml
4
5
v ol um et ric f l a s k and d i l u t i n g w ith glass
s o l u t io n was s t i r r e d u n t i l
d i s t i l l e d water to volume. The
a homogeneous s o l u t i o n re su lt ed .
Dye so lu tio n was made by adding 50 mg 2, 5-dichloroindophenol dye
and 42 mg sodium bicarbonate to a 200 ml v ol um et ric f l a s k and d i l u t i n g
to volume w it h glass d i s t i l l e d w at e r.
The s o l u t i o n was then f i l t e r e d
i n t o a red achnic glass f l a s k and stored in a r e f r i g e r a t o r .
Ascorbic acid standard was achieved
by p l ac in g 100 mg ascorbic acid
i n t o a 100 ml volumetric f l a s k and d i l u t i n g to volume with the
ac e ti c- pho sp hor ic acid mix.
Duplicate determinations were made on each
t re a tm e n t.
Crude L i p i d Determination
The potatoes were separated into p i t h and cortex se c tio ns , f r o z e n ,
l y o p h i l i z e d in a Stokes f r e e z e - d r y e r and ground in a Wiley M i l l
a 40 mesh screen.
analyzed.
The r e s u l t i n g powder was stored under nitrogen u n t i l
Only the cort ex t i s s u e powder was used f o r determination of
crude l i p i d .
a l.,
through
Crude l i p i d was ex tr act ed from the potato powder (Mondy e t
1963) and expressed on a dry weight ba s is .
A 40 gram sample of
dehydrated powder was combined with a solve nt con sis tin g of chloroform
and methanol
( 2 : 1 ) and s t i r r e d f o r three hours under nitrogen w it h a
magnetic s t i r r e r .
The r e s u l t i n g sol ut ion was f i l t e r e d through s i n t e r e d
glass w it h the residue being taken up in fre sh solvent and then s t i r r e d
again f o r one and o n e - h a l f hours p r i o r to f i l t r a t i o n .
The f i l t r a t e s
from both ex t r a c t s were then combined.
Water soluble i m p u r i t i e s were freed from the f i l t r a t e using a
s o l u t io n o f magnesium c h l o r i d e (0.035%) in chloroform:methanol :magnesium
6
chloride ( 8 :4 :3 ) .
The s ol ut io n s were shaken t og et he r and stored under
n itr og en overnight in a f r e e z e r .
The f o l l o w i n g day the upper phase was
drawn o f f by su c ti o n , dis ca rd e d, and the lower phase washed twice with
small amounts of so l v e n t.
The solvent was removed using a r o t a r y
e v a p o r a t o r , and the sample which then contained the crude l i p i d was
stored under nitrogen over phosphorus pentoxide u n t i l
i t reached a
constant weight.
Phospholipid F r a c t i o n a t io n
Crude l i p i d was f r a c t i o n e d into an acetone soluble po r t io n ( n e u t r a l
f a t s , f r e e f a t t y acids and uns ap on ifi ab le s) and an acetone i n s o l u b l e
po rt io n (phospholipids) as described by Mondy e t a l . ( 1 96 5 ).
F i r s t the
crude l i p i d sample was combined with 15 ml o f acetone and stored under
nitrog en in a r e f r i g e r a t o r over ni g h t .
The next day the acetone
i n s o l u b l e phospholipids were f i l t e r e d from the s o l u t io n .
The f l a s k was
rinsed and the sample washed w ith 21 ml o f acetone in 3 ml p o r t io n s .
The acetone s o lv en t, which contained ne u tra l
f a t t y aci ds, f r e e f a t t y
acids and u n s ap o n if ia b le s, was evaporated using a f la s h evap orat or.
The in soluble phospholipids were contained in the f i l t e r paper,
which was then returned to the f l a s k , d r i e d w ith nitrogen and stored
wit h 15 ml chloroform and methanol
r e f r i g e r a t o r ove rn igh t.
( 2 : 1 ) under nitrogen in the
The chloroform-methanol e x t r a c t con tai ni ng the
phospholipids was f i l t e r e d the fo ll o w in g day.
Ten ml of fresh
chloroform-methanol mixture was added to the f l a s k and returned to the
r e f r i g e r a t o r f o r one hour p r i o r to r e f i l t e r i n g
complete removal o f the sample from the f l a s k .
in order to ensure
This washing step was
7
performed three times in t o t a l .
Flash evap oration next removed the
s o l v e n t , and the sample was stored under n itr og en over phosphorus
pentoxide u n t i l
constant weight.
F a t t y Acid Analysis
All
phospholipid samples were methylated f o r f a t t y acid a n a l y s i s .
The phospholipid samples were equally d iv id ed between two 4 dram v i a l s
using chloroform and methanol
of nitrogen.
( 2 : 1 ) , w it h each being dr ie d under a j e t
The phospholipid samples were dissolved using a vort ex
mixer in 2. 0 ml of sodium hydroxide s a p o n i f i c a t i o n reagent (IN NaOH)
which consisted o f 4 . 0 gms NaOH, 60 ml methanol, 40 ml benzene and 15 ml
phe nolphthalein.
HCl/methanol
The sample was n e u t r a l i z e d w it h 15 ml o f 10 percent
(supelco) and again mixed.
Complete conversion to est ers
was i n d ic a t e d by a tra ns fo rm at io n of the cloudy s o l u t i o n , which became
acid to li t m u s .
The sample was stored under nitrogen in the
re frig e ra to r until
i n j e c t i o n i n to the gas chromatograph.
Separation o f the methyl esters o f the f a t t y acids was achieved
using a var ia n Aerograph s e r i e s 2100 gas chromatograph employing a flame
detector c e ll.
The s t a t i o n a r y phase used was apiezon L, a non -polar
p o l y e s t e r of succinic a ci d .
Preparation o f the columns and the
ope ra tin g parameters f o r the instrument have been described in d e t a i l
McNair and Bonelli
(1967).
R e la t i v e r e t e n t i o n volume on a p o l a r and
no n-polar s t a t i o n a r y phase, and e s t a b l i s h i n g a g r i d using known acid
stamdards were employed to i d e n t i f y the f a t t y acids.
i n t e g r a t i o n was used to q u a n t i t a t e the acids.
Peak-area
by
8
Determination o f Phenols
The potatoes were l o n g i t u d i n a l l y s l i c e d from bud to stem end so
t h a t the cortex section could be removed f o r a n a ly s is .
F i f t y grams of
co rt ex was blended w ith 100 ml o f 95% ethanol in a Waring blender f o r
t h r ee minutes.
obtained.
The s l u r r y was f i l t e r e d u n t i l 35 ml o f f i l t r a t e was
Appropriate a l iq u o ts o f e x t r a c t were p i p e t te d i n t o 100 ml
vol umetric f l a s k s conta in in g 80 ml o f d i s t i l l e d w ater.
The most
f r e q u e n t l y used l e v e l s of e x t r a c t s were 0 . 4 , 0. 5 and 0 . 6 ml.
level
At each
of e x t r a c t , t r i p l i c a t e determinations were made.
The c o l o r i m e t r i c method o f Rosenblatt and Peluso (1941) was used to
determine the t o t a l
phenolic co n te n t, which is based on the r e a c ti o n of
Fol in -D eni s reagent w ith phenolic compounds in an a l k a l i n e s o l u t i o n .
Following the a d d i t i o n o f the e x t r a c t , 2.5 ml of Fol in -D en is and 5.2 ml
o f saturated sodium carbonate were added to each vol um et ric f l a s k .
The
so lu tio ns were then d i l u t e d to volume and immediately mixed by i n v e r t i n g
the f l a s k s .
Full c o l o r development was achieved by al lo wi ng the
so lu tio ns to stand f o r 70 minutes f o l l o w i n g the a d d it io n of the sodium
carbonate.
Percent tra nsm ittanc e o f the solutions were read on a Bausch
and Lomb Spectronic 20 using a #660 f i l t e r .
Two e x t r a c t s and one set of t an ni c acid standards were run in
sequence by c o n t r o l l i n g the timing of the ad d iti on of reagents and the
readings on the c o l o r i m e t e r .
standard ( 0 . 5 ,
D uplicates were made a t each l e v e l
of
1 . 0 , 1.5 and 2 . 0 m l ) , containing 0.1136 mg o f t an ni c acid
per ml of s o l u t i o n .
A blank which contained only Fol in -D en is and sodium
carbonate was run a t each deter m in ati on.
The f i n a l
phenolic
9
concentration was expressed as m ill ig r a m s o f ta nnic acid per 100 g of
f re sh t is s u e .
The t ann ic acid standard con centration was 0.1136 g / l i t e r .
The
s o l u t io n was prepared on a weekly basis and was stored in the
refrigerator.
Fo l in -D e n i s reagent was prepared by r e f l u x i n g an aqueous
s o l u t io n of 112 g of sodium t u n g s t a t e , 20 g of phosphomolybdic acid and
128.5 g of 35 percent metaphosphoric ac i d .
The so lu t io n was cooled and
d i l u t e d to volume in a one l i t e r volu met ric f l a s k f o l l o w i n g two hours of
refluxing.
Addition o f 350 grams o f NagCOg to 2 l i t e r s o f d i s t i l l e d water
r e s u l t e d in the sa t u r at ed sodium carbonate.
D i s c o lo r a t i o n Determination
Color measurements were made using the cortex t i s s u e o f the
potatoes by the method o f Mondy e t a l .
D i f fe r e n c e Meter.
(1967) using the Hunter Color
The standard grey t i l e
(Rd = 3 9 . 0 , a = - 1 . 1 ,
- 3 . 3 ) was used to c a l i b r a t e the instrument.
and b =
Only Rd values are reported
since these were most cl o s e l y r e l a t e d to the potato d i s c o l o r a t i o n
v i s u a l l y observed. An increase in Rd corresponds to decrease in
discoloration.
P r i o r to being ground f o r co lo r measurements, the potatoes were
peeled by hand w ith an ordin ar y vegetable p e e le r .
potatoes was used f o r each deter m in ati on.
Tissue from fo ur
Only cortex t i s s u e was used
since t h i s is the area known to d i s c o l o r most r e a d i l y fo ll o w in g
bruising.
A 200 g sample was then ground in a food g r i n d e r using the
"coarse" attachment.
A f t e r being allowed to stand a t room temperature
10
f o r 20 minutes the ground sample was t r a n s f e r r e d to a cup w it h an
optical
glass bottom so t h a t the c o l o r r e f l e c t a n c e readings could be
immediately taken.
Color comparisons were also made using the chl or of or m -d is c method
(Mondy and M u e l l e r , 197 7) .
A co re , o n e - h a l f inch in diameter running
from bud to stem end was removed from the center o f the tuber using a
s t a i n l e s s steel bo r e r .
The borer was c a l i b r a t e d so t h a t the core could
be uniformly advanced by a distance of 1 mm.
i n t o 1 mm discs w ith a s t a i n le s s st eel
an atmosphere o f chloroform.
Each core was cut r a p i d l y
blade and placed immediately in to
Visual observations o f the e x t e n t of
d i s c o l o r a t i o n were made a t 15 minute i n t e r v a l s .
Total Nitrogen Determination
For the deter min ati on of t o t a l
AOAC (1975) was used.
nitrog en the method described by
Approximately 100 mg of f re e z e d r ie d powder of
potato cortex t i s s u e , 2 . 2 ± 0.1 g o f potassium s u l f a t e and 0 . 2 g of
mercuric oxide were added to a m ic ro -K je ld ah l f l a s k .
concentrated s u l f u r i c acid (sp. g r .
acid.
2 ml of
1. 84) was added as the dig est ion
The mixture was digested f o r 4-5 hrs. and then d i s t i l l e d
m icro -Kje ldah l d i s t i l l a t i o n apparatus.
t i t r a t e d against HC1.
The r e s u l t a n t d i s t i l l a t e was
A mixed i n d i c a t o r (methyl
was used to measure the completion o f t i t r a t i o n
red-bromcresol
^
_
green)
(a l i g h t v i o l e t c o l o r ) .
Total nitrogen was ca l c u l a t e d by using the fo llo w in g formula:
o
in a
[(mL HC1 - ml blank) X nor m al ity X 14.007 X 100]
mg sample
11
Non-Protein Nitrogen
Non-protein nitrog en was determined using t r i c h l o r o a c e t i c acid
(TCA) p r e c i p i t a t i o n o f f re ez e dr ie d potato powder.
A modified version
o f the method by Desborough and Weiser (1974) was used.
Approximately
250 mg o f the f r e e z e d r i e d powder was taken i n to a 50 ml Erlenmeyer
f l a s k and 25 ml of 10% TCA was added.
The contents were s t i r r e d f o r 1
hr on a Fisher Thermix magnetic s t i r r e r ,
then t r a n s f e r r e d to 50 ml
p l a s t i c c e n t r i f u g e tubes and ce n tr if u g e d a t 10,000 X g in a S o n /a ll
u l t r a c e n t r i f u g e f o r 10 minutes.
Whatman No. 1 f i l t e r paper.
RD-5
The contents were then f i l t e r e d through
Ten ml o f f i l t r a t e was taken and nitrogen
determination was made in the same manner as described f o r t o t a l
n i tr o g e n .
Percent Protein
Protein ni tro ge n was c a lc u la t ed by d i f f e r e n c e of no n- pr ot ei n
ni tro ge n from t o t a l
ni tr o g e n .
Percent p r o t e i n was c a l c u l a t e d by using
the Kjeldahl f a c t o r o f 7. 5 f o r potatoes (Desborough and Weiser, 1974).
E x tra c tio n and Q u a n t i t a t i o n of Free Amino Acids
Free amino acids were ex tr act ed from the f r e e z e - d r i e d potato powder
using 70% ethanol as described by Weaver e t a l .
( 1 97 8 ).
Approximately
100 mg of the f r e e z e d r i e d powder was placed in a 50 ml Erlenmeyer f l a s k
and 10 ml o f 70% ethanol was added.
The contents were s t i r r e d f o r 1 hr
on a Fisher Thermix magnetic s t i r r e r , then t r a n s f e r r e d to a 50 ml
p l a s t i c c e n tr i fu g e tubes and ce n tr if u g e d a t 10,000 X g in a So rvall RC-5
u l t r a c e n t r i f u g e f o r 10 minutes.
The supernatant was then f i l t e r e d
12
through Whatman No. 2V f i l t e r paper i n t o a 100 ml round bottom f l a s k .
The f i l t e r paper was rinsed th re e times wit h 5 ml o f 70% alcohol and the
t o t a l f i l t r a t e was evaporated using a r o t a r y evaporator.
The volume was
made to 10 ml with glass d i s t i l l e d w ate r using a 10 ml vol um et ric f l a s k .
A one ml port io n was removed and 50 mg o f s u l p h o s a l i c y l i c aci d was
added.
M ixt ure was cen tri fu g ed a t 1000 rpm f o r 10 minutes and an
a l i q u o t of t h i s mixture was i n j e c t e d i n t o an amino acid a n a l y z e r .
Ion
exchange column chromatography technique of Spackman e t a l . (1958) was
used f o r the q u a n t i f i c a t i o n of amino acids using a Technicon TSM Amino
Acid Analyzer w ith phy siological f l u i d columns.
Norleucine was used as
the i n t e r n a l standard.
Total Amino Acids
•
50 mg potato powder and 2 ml HC1 (6N) were placed in an ampule.
The ampule was sealed and the contents digested in an o i l
f o r 18 hours.
bath (110°C)
The t o t a l contents were t r a n s f e r r e d wit h a Pasteur
p i p e t t e i n t o a t e s t tube and evaporated to dryness.
5 ml o f HC1 b u f f e r
(.0 1 M) was added to the t e s t tu be , which was then mixed and
centrifuged.
An a l i q u o t of the supernatant was i n j e c t e d i n t o an amino
acid an al yze r as previously described.
Mineral Analysis
The mineral
content of f r e e z e - d r i e d potato powder was analyzed by
atomic emission spectroscopy using an i n d u c t i v e l y coupled plasma system
13
as described by Fassel and Kniseley ( 1 9 7 4 ) .
The system is based on the
observation of atomic emission spectra when the powdered sample is
i n je c t e d i n t o an i n d u c t i v e l y coupled plasma at om iza tio n and e x c i t a t i o n
source.
The i n d u c t i v e l y coupled, r ad io frequency plasma is produced in
a vertical
quartz tube which is surrounded l o n g i t u d i n a l l y by a c o i l
carrying an o s c i l l a t i n g e l e c t r i c a l
eddy curre nts in the plasma.
th e ir flow,
cu r r e n t which, in t u r n , generates
These c u r r e n t s , encountering r esi st anc e to
r e s u l t in Joule he a tin g.
Argon was the c a r r i e r gas.
Sampling Procedure
Potatoes o f comparable s i z e were selected from each treatment in
order to l i m i t v a r i a t i o n s due to siz e d i f f e r e n c e s .
Tubers were cut
longitudinally
from bud to stem end in order to obt ai n equal sampling
both ends, and
s l i c e s were separated i n t o cortex and p i t h sections.
Statistical
of
Analyses
Data were
with protected
analyzed using the t - t e s t or a na ly s is of variance (ANOVA)
LSD t e s t as described by Steel and T o r r i e (19 60 ).
MAGNESIUM STUDY
I n t r o d u c t io n
Magnesium is an e s s e n t i a l m i c r o n u t r i e n t in p l a n t metabolism.
i ncorporated i n to ch lo ro ph y ll and is also involved in the
o r g a n iz a t i o n of o th er c on st it ue nt s w i t h i n the c e l l .
and 50S ribosomal subunits to form
I t is
structural
The binding o f 30S
a 70S ribosome is dependent on the
magnesium ion con centration ( H e w it t and Smith, 197 4) , and magnesium may
also f u n c t io n to s t a b i l i z e the s t r u c t u r e of membranes.
Kahone e t a l .
(1973) found t h a t magnesium was the major c at io n associated w it h the
l i p i d f r a c t i o n of A. l a i d l a w i i membranes, and suggested t h a t d i v a l e n t
cations s t a b i l i z e membrane st ruc tu re s by forming i n t r a - and i n t e r molecular cross l i n k s , such as between phosphate groups o f membrane
phospholipids and carboxyl
groups o f membrane p r o t e i n s .
Magnesium is
also required n o n s p e c i f i c a l l y by a la r g e number of enzymes involved in
phosphate t r a n s f e r and is necessary f o r the production o f ATP.
Yield
Potatoes are more s e n s i t i v e to magnesium d e f i c ie n c y than many other
crops ( B ol to n, 197 7) , y e t such d e f i c i e n c i e s may be corrected through the
use o f magnesium s u l f a t e in f e r t i l i z e r s
Houghland, 1964).
the p r i n c i p a l
(Houghland and Strong, 1941;
In acid peat and sandy s o i l s magnesium d e f i c i e n c y is
cause o f poor growth (Mulder, 1950).
Response to
magnesium is p a r t i c u l a r l y apparent on acid and sandy loams which also
contain less than 76 lb o f exchangeable magnesium/acre and have a pH
14
15
below 5.5 (D oll and Thurlow, 196 5).
Sawyer and Dallyn (1966) found th a t
y i e l d s were maximized when potatoes grown on s o i l s adequate in magnesium
were f e r t i l i z e d w it h 40 l b / a c r e magnesium s u l f a t e (oxide e q u i v a l e n t ) ,
and t h a t 40-60 l b / a c r e was adequate in b u i l d i n g up and m ai nta ini ng the
lower soi l
l e v e l s found on Long I s l a n d .
Laughlin (1966) observed t h a t
s o i l or spray a p p l i c a t i o n s of magnesium s u l f a t e had no s i g n i f i c a n t
e f f e c t on y i e l d , y e t magnesium s u l f a t e was applied to the s oi l a t high
rate s of 250 and 500 l b / a c r e , and s o i l
suggested alre ady high f e r t i l i t y
a v a i l a b l e magnesium.
analyses p r i o r to f e r t i l i z a t i o n
l e v e l s ranging from 119 to 350 l b / a c r e
An e f f e c t on y i e l d would not be apparent wit h such
high l e v e l s o f magnesium since the e f f e c t i v e n s s of magnesium f e r t i l i z a ­
t i o n occurs only over a small range o f a p p l i c a t i o n r a t e s .
At high rates
y i e l d s tend to approach values produced when no magnesium is a p p lie d.
Adams e t a l .
(1978a) observed t h a t y i e l d s o f tomatoes grown in peat
demonstrated an o v e r a l l
increase in y i e l d o f 8.6% with added magnesium
but n e i t h e r the q u a l i t y nor the composition was a f f e c t e d .
Adams e t a l .
(1978b) also found, however, t h a t l e t t u c e grown in peat did not respond
to added magnesium.
These authors suggest t h a t such r e s u l t s are consis­
t e n t with e a r l i e r t r i a l s which demonstrate t h a t l e t t u c e is not severely
a f f e c t e d by magnesium d e f i c i e n c y , whereas tomato crops are hi ghl y
su s ce p t ib le .
D i s c o lo r a t i o n and Phenolic Content
The phenolic content of potato tubers shows a p o s i t i v e c o r r e l a t i o n
wit h enzymatic darkening (Mondy e t a l . ,
196 7).
B it ter ne ss and
16
astringency o f cooked potatoes has also been shown to be p o s i t i v e l y
c o r r e l a t e d (Mondy e t a l . , 197 1).
Chlorogenic acid (an e s t e r o f c a f f e i c
and qui ni c ac id s) and t y r o s i n e have been shown to be the two major
phenolic compounds responsible f o r enzymatic d i s c o l o r a t i o n o f the
potato.
Chlorogenic acid is predominantly located in the cortex tiss ue
w h il e t y r o s i n e is found mainly in the p i t h region o f t ub er s.
The
production o f dark colored pigments or melanins from phenolic substrates
occurs f o l l o w in g t i s s u e damage, when su bs tra te and enzyme mix in the
presence of oxygen.
Melanins polymerize from orthoquinones, which have
themselves been formed as a r e s u l t o f enzymatic o x i d a t i o n of phenolic
su b st r at es .
Any f a c t o r t h a t r e s u l t s in damage to t i s s u e or in an
increase in the l e v e l
an enhanced le v e l
o f phenolic compounds of t h a t t i s s u e may lead to
of blackening in the potato tuber.
The e f f e c t o f magnesium on tub er d i s c o l o r a t i o n has been v a r i a b l e .
Length of time p r i o r to analysis may r e s u l t in an i n c r e a s e , decrease, or
i n s i g n i f i c a n t e f f e c t on black spot production in potatoes (Jacob, 1959).
M ue lle r (1976) observed t h a t m a g n e s iu m - f e r ti li z e d tubers discolored more
than control tubers 1 month f o l l o w i n g harvest y e t d i s c o l o r a t i o n was
s i g n i f i c a n t l y less than t h a t f o r con tro ls a f t e r 10 months o f storage.
Supplementation o f magnesium with potassium decreased d i s c o l o r a t i o n ,
whereas magnesium f e r t i l i z a t i o n
on i t s own increased d i s c o l o r a t i o n
(Massey, 1952).
Li pids
The average l i p i d content o f potato tubers is around 0.1% on a
f re sh weight ba s is , w ith the m a j o r i t y being concentrated in the periderm
17
and cortex t is s u e (Smith, 1 9 7 7) .
to con sist o f 16.5% neutral
Lepage (1968) found the l i p i d content
l i p i d s , 45.5% phospholipids and 38.1%
g l y c o l i p i d s w hi le the f a t t y acid content predominantly consisted of
44.8% l i n o l e i c , 30.4% l i n o l e n i c and 19.5% p a l m i t i c .
Magnesium increased the f a t content o f sunflower seeds (Maslow,
1938) and soybeans (Almeida, 193 8) .
Reed (1947) found t h a t f il a m e n t s of
vaucheira grown in magnesium-free solutions were devoid of o i l
gl o b u l e s ,
y e t f il a m e n t s o f plants grown in magnesium so lu t io n s contained o i l
globules.
Nitrogen
Approximately 1-2% o f t ub er dry weight i s composed of n i tr o g e n ,
with p r o t e i n ni tro ge n as 37.0-63.7% of the t o t a l
1942).
(Neuberger and Sanger,
Desborough and Weiser (1974) re po rt t h a t potato protein is
approximately 13.5% n itr og en .
Pr ot ei n content o f potatoes is about
1-1.5%, and p r o t e i n amino acid content is almost e q u iv a le n t to ca s ei n ,
as well con taining ly si ne (Gr oot , 1945).
The complementation o f potato
pr otein with o t h e r foods o f non-animal o r i g i n t h a t are d e f i c i e n t in
ly si ne can provide an important c o n tr i b u t io n to the d i e t , e s p e c i a l l y of
those people who depend h e a v il y on grains to comprise a m a j o r it y of
t h e i r dietary staple.
Potato tu ber proteins are about 60-70% gl obu lin s
and 20-40% g l u t e l i n s , with no albumins or prolamines present.
Free
amino acids comprise 40-50% of nonprotein nitrogen (Tavrovskaya, 1964).
Groot e t a l . (1946) found t h a t the t o t a l
t u b e r i n i n and 70% t u b e r i n , and Holzl
p r o t e i n consists of 30%
and Bancher (1961) found t h a t
18
t u b e r i n contains s u f f i c i e n t amounts of e s s e n t ia l
amino acids needed f o r
growth except f o r methionine.
The a p p l i c a t i o n o f magnesium is reported to increase the nitrog en
content o f potato pl ants (Estes and Gausman, 1 9 6 1) .
On sandy s oi l
magnesium a p p l i c a t i o n enhanced the uptake o f n i t r o g e n , prolonged the
growth period and increased the y i e l d o f tubers o f an e a r l y v a r i e t y
( T u l i n , 197 5).
Laughlin (1966) found no e f f e c t o f magnesium
f e r t i l i z a t i o n on the t ub er content of n i t r o g e n , although l e v e l s o f
a p p l i c a t i o n were very high (250 and 500 l b s / a c r e ) .
Minerals
With the exception o f calcium, the white potato ( Solanum tuberosum
L . ) contains most of the minerals f o r which U.S.
recommended d i e t a r y
allowances have been e s t a b l i s h e d ( i r o n , copper, i o d in e , magnesium,
phosphorus, and zi nc )
(True e t a l . , 1978).
The potato is r e l a t i v e l y low
in sodium but an e x c e l l e n t source of potassium.
The minerals calcium,
i r o n , manganese and boron concentrate more in the cortex than p i t h
tissue.
The magnesium content o f potato tubers was increased f o ll o w in g
magnesium f e r t i l i z a t i o n
(Vermes et a l . ,
197 4).
The add ition of
magnesium to a nitrogen-phosphorus-potassium f e r t i l i z e r reduced the
potassium and manganese c o n te n t, and increased the magnesium content o f
snap bean leaves and the t o t a l
pl ant (P alaniyandi and Smith, 1978).
19
Firmness
Texture is an important q u a l i t y f a c t o r o f potatoes.
There is a
high c o r r e l a t i o n between t e x t u r e o f cooked or processed potatoes and the
s p e c i f i c g r a v i t y or dry m at te r content o f the raw potatoes. Mealy
t e x t u r e i s associated w it h high solids and leads to improved baking and
processing q u a l i t i e s .
As judged by sensory means, however, exceptions
are found to a c o r r e l a t i o n between s p e c i f i c g r a v i t y and mealiness
(Sm ith, 1977).
To ev a lu a te prope rly f o r mealiness, o b j e c t i v e methods
are d e s i r a b l e .
Lujan and Smith (1964) used the modified L.E .E .-K ra m er
shear press and were able to d e t e c t t e x t u r a l
d i f f e r e n c e s between tubers
which d i f f e r e d from each o t h e r by 0.002 or less in s p e c i f i c g r a v i t y .
The s p e c i f i c g r a v i t y o f raw tubers is the best estimate o f mealiness,
and the r esi st anc e o f raw t ub er cubes to a pressure fo rce is
s i g n i f i c a n t l y c o r r e l a t e d w it h t h e i r s p e c i f i c g r a v i t y (Lujan and Smith,
1964).
An instrument such as the Instron Universal Testing machine can
s
thus provide an i n d i c a t i o n o f potato tu ber t e x t u r a l q u a l i t y through a
measurement of firmness.
Mineral n u t r i t i o n may a f f e c t the t e x t u r e o f the t ub er .
Phosphorus
a p p l i c a t i o n to the p l a n t may a f f e c t the s p e c i f i c g r a v i t y o f the potato
(Zandstra e t a l . ,
196 9).
Sloughing o f the cooked product can be reduced
by trea tme nt with calcium ( S t e r l i n g and B e tt e l h e i m , 1955).
The presence
o f calcium and magnesium in c e l l w alls has been associated w ith metal
bridges between pectin molecules, and a f i r m e r t e x t u r e in cooked tubers
(Bartolome and H o f f , 1972).
20
The purpose o f the present i n v e s t i g a t i o n was to study the e f f e c t of
magnesium f e r t i l i z a t i o n
on y i e l d , enzymatic d i s c o l o r a t i o n , phenols,
l i p i d s , nitrogenous c o n s t i t u e n t s , minerals and firmness f potato tubers.
M a t e r i a l s and Methods
Katahdin potatoes grown a t the Cornell Vegetable Research Farm a t
Riverhead, Long I s l a n d , during th re e growing seasons were used in the
study.
During the t h i r d season n i t r o g e n , mineral and firmness
determinations were only conducted.
loam.
Soil
type was Riverhead f i n e sandy
Magnesium in the form of magnesium s u l f a t e (MgSO^) was banded a t
p l a n t i n g a t ra te s of 0 , 20, 40 and 100 lbs per acre during the f i r s t two
y e a r s , and a t 0 , 40 and 100 lbs per acre the t h i r d y e a r .
The randomized
block design contained two r e p l i c a t e d p l o t s per tre a tm e n t.
o f a v a i l a b l e min erals on these pl o t s was as fo ll o w s :
The l b s / a c r e
Magnesium 70,
phosphorus 4 3 . 4 , potassium 219, calcium 2240, manganese 12.6 and zinc
2.4.
Soil organic m at te r averaged 2.91%, and soi l
p l o t s were i r r i g a t e d .
pH was 6 . 1 2 .
All
Tubers were harvested 24 weeks a f t e r pl an tin g and
stored a t 5°C f o r 5 months p r i o r to a n a l y s i s .
The determinations o f enzymatic d i s c o l o r a t i o n , phenols, l i p i d s ,
nitrogenous c o n s t i t u e n t s , minerals and firmness were made according to
methods pr evi ous ly described in the general experimental
cha pter.
Cortex t i s s u e was used f o r a l l
because of i t s high metabolic a c t i v i t y .
procedure
determinations except firmness
21
Results and Discussion
Yiel d
Maximum y i e l d accompanied the a p p l i c a t i o n of magnesium s u l f a t e a t
the le vel
o f 20 l b / a c r e f o r years 1 and 2 of the study;
it
was
depressed when the le ve l o f magnesium exceeded 40 l b / a c r e ( F ig .
Appendix Table 1 . 1 ) .
( 196 6) .
1.1,
This is in agreement w ith Sawyer and Dallyn
Gen er al ly the y i e l d s obtained at a l l
l e v e l s of magnesium
f e r t i l i z a t i o n were higher during the f i r s t y e a r o f the study.
This was
probably due to seasonal v a r i a t i o n .
Di s c o lo r a t i o n
Tubers r e c e i v i n g 40 l b / a c r e MgSO^ di scolored s i g n i f i c a n t l y
(p < 0 . 0 5 )
less than controls when measured o b j e c t i v e l y with the Hunter
Color D i f f e r e n c e meter ( F i g .
1 . 2 , Appendix Table 1 . 2 ) and were w h i t e r
when s u b j e c t i v e l y assessed by the cholorform disc method ( F ig .
1.3).
These r e s u l t s are in agreement with those found p r ev io us ly in our
la bo ra to ry ( M u e l l e r , 1976).
Phenols
A ll
l e v e l s o f magnesium a p p l i c a t i o n s i g n i f i c a n t l y
reduced the t o t a l
1.3).
phenolic content of tubers ( F i g .
(p < 0. 0 5 )
1 . 4 , Appendix Table
Mondy e t a l . (1967) observed a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n
( r = +0 .8 3) between t o t a l
phenolic content and tuber d i s c o l o r a t i o n .
Lower phenolic content not only reduces s u s c e p t i b i l i t y o f tubers to
black spot but also reduces the b i t t e r t a s t e (Mondy e t a l . ,
1971).
YIELD
<CWT/flCRE>
22
250'
MRENE51UM 5ULFRTE (LS5/RCRE)
Fig.
1.1.
E f f e c t o f magnesium f e r t i l i z a t i o n
Katahdin p o t a t o e s .
on the y i e l d o f
23
2Ht
YERR I
YEfW 2 '
COLOR
<r e fle c th n c e : >
22-
22
”
IB"
I4»
10-1
2
28
H0
122
MRENE5IUM 5ULFRTE <LB5/flCRE>
Fig.
1. 2.
E f f e c t o f magnesium f e r t i l i z a t i o n on t h e d i s c o l o r a t i o n
o f c o r t e x t i s s u e from Ka tah din p o t a t o e s .
Reflectance
v a l u e (Rd) decreases as b l a c k e n i n g i n c r e a s e s .
24
MG 0
•
•
•
•
•
•
•
#
•
•
Fig.
1.3.
MG 40
•
•
\
g
'
%
* . • ,
v
$
•
•
E f f e c t of magnesium on the d i s c o l o r a t i o n o f
cortex t is s u e from Katahdin potatoes assessed
subjectively.
25
B0t
YERR
I
YERR 2
-
701
2
< M E /|0 0 G
Li!
PHENPL
50-
50-
M0i
t
Is T
10
MRENE5 IUM 5LLFRTE <LB5/RCRE>
Fig.
1 .4 .
E f f e c t o f magnesium f e r t i l i z a t i o n on t h e p h e n o l ic c o n t e n t
o f c o r t e x t i s s u e from Katahdin p o t a t o e s .
26
L i p i d Composition
Tubers r e c e iv i n g 40 l b / a c r e MgSO^ were s i g n i f i c a n t l y
higher in crude l i p i d
(Fig.
(Fig.
(p < 0 . 0 1 )
1 . 5 , Appendix Table 1 . 4 ) and phospholipid
1 . 6 , Appendix Table 1 . 5 ) content.
Magnesium may a f f e c t l i p i d
synthesis by f u n c t io n in g as a cof ac to r in the formation of CoA
d e r i v a t i v e s which are involved in f a t t y acid syn thesis.
Magnesium is
r eq ui re d f o r the c a r b o x y l a ti o n of pyruvic acid to form acetyl-CoA.
It
i s also involved in the a c e t i c t h io ki na se system during acetyl-CoA
production from ATP and a c e t a t e , and is requi re d f o r the production o f
malonyl-CoA from acetyl-CoA.
In a d d i t i o n , magnesium is necessary f o r
the e s t e r i f i c a t i o n o f phosphorus i n to ATP and during the i n c l u s io n o f
phosphorus in to phospholipids by mitochondria (M azelis and Stumpf,
1955).
Li pi d s are extremely important in the s t r u c t u r e and f u n c t io n in g of
membranes found in the potato tuber and may play a ro le in determining
potato tu ber s u s c e p t i b i l i t y to d i s c o l o r a t i o n .
Darkening o f t ub er t is s u e
r e s u l t s from the r e a c ti o n of phenolic substances with polyphenol
oxidase.
Tubers w it h a higher l i p i d content have been shown to be less
s u s c e p t ib le to damage f o l l o w i n g br uis ing (Mondy and Koch, 1978).
Reduced rupt ur ing may t h e r e f o r e decrease the opp ortunity f o r phenolase
enzymes to i n t e r a c t wit h phenolic substances which are normally
separated by membranes, thus r e s u l t i n g in reduced enzymatic
discoloration.
An increase in both crude l i p i d and phospholipid
contents o f Katahdin potatoes fo llo w in g magnesium f e r t i l i z a t i o n
is in
agreement w ith p r e l im i n a r y studies from our l a b o r a t o r y ( M u e l l e r , 1976).
-X
CRUDE
LIPID
<MG/G
27
22
HB
IBB
MRENE51UM 5L1LFRTE (LB5/RCRE)
Fig.
1. 5 .
E f f e c t o f magnesium f e r t i l i z a t i o n on t h e cr ude l i p i d
c o n t e n t o f c o r t e x t i s s u e from Katahdin p o t a t o e s .
28
YEAR
I ------
PHOSPHOLIPID
<
MG/E
YERR 2 ------
MRGNE5IUM 5ULFHTE <LS5/RCRE>
Fig.
1.6.
E f f e c t o f magnesium f e r t i l i z a t i o n on t h e p h o s p h o l i p i d
c o n t e n t o f c o r t e x t i s s u e from Katahdin p o t a t o e s .
29
The content o f l i n o l e i c acid in potatoes t r e a t e d w it h MgSO^ was
s i g n i f i c a n t l y (p < 0 . 0 5 ) reduced w h il e the content o f l i n o l e n i c acid was
s i g n i f i c a n t l y (p < 0 .0 5)
Appendix Table 1 . 6 ) .
increased during yea r 1 o f the study ( F i g .
1.7,
However, no s i g n i f i c a n t changes were observed in
any o f the f a t t y acids during y e a r 2 ( F i g .
1 . 8 , Appendix Table 1 . 6 ) .
These d i f f e r e n c e s may be a t t r i b u t e d to seasonal v a r i a t i o n .
Total Nitrogen
The t o t a l
nitrogen content o f tubers was s i g n i f i c a n t l y (p < 0 . 0 5 )
increased by magnesium s u l f a t e f e r t i l i z a t i o n a t 40 and 100 l b s / a c r e
during t h r ee years of the study ( F i g .
1 . 9 , Appendix Table 1 . 7 ) .
Laughlin (1966) found no e f f e c t o f MgSO^ f e r t i l i z a t i o n
on the nitrogen
content o f potato t ub er s, but l e v e l s o f a p p l i c a t i o n were excessively
high (250 and 500 l b s / a c r e ) .
Palanyandi and Smith (1978) found t h a t the
ad d it io n o f magnesium to an N, P, K f e r t i l i z e r reduced the content o f
nitrogen in snap bean leaves although no e f f e c t was found f o r the t o t a l
p l a n t s , which suggests t h a t magnesium may have increased the t o t a l
nitrogen content o f the beans.
Non-Protein Nitrogen and Prot ein
The non-protein nitrogen content of tubers was increased during
year 1 o f the study, y e t decreased during years 2 and 3 ( F ig .
Appendix Table 1 . 7 ) .
Protein c o n te n t, however, was increased by 40 and
100 l b s / a c r e magnesium s u l f a t e during a l l
Appendix Table 1 . 7 ) .
1.10,
three years ( F i g .
1. 11 ,
Magnesium is required f o r the a c t i v a t i o n ,
i n i t i a t i o n and elongation steps o f p ro te in synthesis.
30
YEAR
FATTY
ACID
< PERCENT>
S0T
na­
il"
20
»
1 0-
Fig. 1.7.
E E E E
\ \ \ \
m in in ui
to til tn cn
H H X H
\ \ \ \
in in in in
to tn tn in
E E
\ \
in in
tn cn
j j j j
j
j j j j
□ H □ H
N T H
C9 SI B □
NTH
S □ HI El
N T S
ffiU H T IC
STEARIC
LINOLEIC
j
j
j
E E
S \
in in
a tn
E E E E
\ \ \ \
in in in in
tn tn tn cn
j j j j
LINOLENIC
E f f e c t o f magnesium f e r t i l i z a t i o n on t h e f a t t y a c i d
c o m p o s i ti o n o f c o r t e x t i s s u e from Ka tah din po ta to es
grown d u r i n g y e a r 1.
31
YERR 2
FRTTY
RC 11>
< PERCENT
>
S0T
H0-
30-
20
-
10-
CE e E E
Fig.
1.8 .
E E E E
E E E E
\ \ \ \
\ \ \ \
in in m in
to cn tn a
j j j j
□a□□
T □
\ \ \ \
in in in in
Cfl a tn tn
j j j j
□□□3
Hi j □
j j j j
□□□3
Nj □
PF1LMIT1C
STEERIC
LINOLEIC
in in in in
tn tn tn tn
E E E E
\ \ \ \
in in in in
to to a a
j j j j
a a a a
IN j a
LINOLENIC
E f f e c t o f magnesium f e r t i l i z a t i o n on th e f a t t y a c i d
c o m p o s i t i o n o f c o r t e x t i s s u e from Katahdin po ta to e s
grown d u r i n g y e a r 2.
of
32
nitrogen
content
H) “J
■lllmlllllllllllllllllllllllllmlll!
Effect
of
i^lllllH IIIIIIIIIIIIIIH lllllllllllllim H
Q
o
Q
00
Q
<o
o
o
cvi
cr>
• M ’Q / B ui
C7>
LU
•r—
tubers.
o
potato
<
►
—
MaSO^
application
Y«ar
■■immmimiimMiiiiimimmmiiiiimmimimm
Katahdin
O
o
a*
on the
total
z
ui
g>j
5 =
1
°
nitrogen
°
@
non-protein
dtg
content
33
o
0
QC
z
o
z
o
d
MO
o
o
oo
(b
S/6U1
A J
Fig.
o
cl
1.10.
Effect
H B llllllllllllllllllllltllllll
of
MgSO^
Qu
1
tubers.
UJ
{=■
o
0
>■
potato
Cl
iiiHniiiiiiiHiiinniimmiiimiiHiiininimmii
Katahdin
z
z
of
h*
application
on the
o
m
■
of
m
o
o
iiiiiiiiiiiiiiiiiiiiiiiii
d
o
(O
M a %
- OA
J
Fig.
o
00
1.11.
Effect
of
MgSO^
£
tubers
■ ■ ■ ■ liiiiiiiiiiiiiiiiiiiiiiiin i
ot
Q.
potato
o
O
Katahdin
a
application
on the
I^ H
protein
content
Mg SC
(ibs/A)
o
40
34
35
Although the pr o t e i n content o f the potato is only about 2%, the
n u t r i t i v e value is very high.
Since the potato is a source o f high
q u a l i t y p r o t e i n , an increase in the p r o t e i n content as a r e s u l t of
magnesium f e r t i l i z a t i o n
is n u t r i t i o n a l l y b e n e f i c i a l .
Amino Acids
Because o f i n i t i a l
r e s u l t s found f o r t o t a l
nitrog en and pr ot ei n
conte nt , amino acid content was determined during y e a r 1 o f the study.
The summation o f f r e e amino acids was increased by approximately 9% and
5% at the 40 and 100 l b / a c r e ra te s o f a p p l i c a t i o n , however, i n d iv id u a l
amino acids demonstrated d i f f e r e n t trends (Table 1 . 1 ) .
General
increases in f r e e amino acid content were observed f o r a s p a r t i c a ci d ,
asparagine, l e u c i n e , phe nyl ala nine , and l y s i n e .
General decreases were
observed f o r ser in e and methionine, w hi le th r e o n in e , glutamic a c i d ,
glutamine, p r o l i n e , g l y c i n e , a l a n i n e , v a l i n e , i s o l e u c i n e , t y r o s i n e ,
h i s t i d i n e , a r g i n i n e and y-aminobutyric acid showed l i t t l e
or
i n co ns is te nt trends.
The summation o f t o t a l
(hydrolyzed) amino acids o f tubers was
increased by approximately 12% in response to magnesium s u l f a t e
a p p l i c a t i o n a t 40 and 100 l b s / a c r e (Table 1 . 2 ) .
observed f o r a l l
General
increases were
amino acids except glutamic a c i d , methionine and
y-aminobutyric a c i d , which were i n c o n s i s t e n t .
An increase in t o t a l
amino acids in agreement with the increases found f o r t o t a l
pr ot ei n fo ll o w in g magnesium f e r t i l i z a t i o n .
nitrogen and
36
Table 1 . 1 .
The e f f e c t o f MgSO. f e r t i l i z a t i o n on the f r e e amino acid
content (mg/g D.W.j o f Katahdin potato tubers (Year 1 ) .
MgSO^ ( Ib s / A c r e )
Amino Acids
0
20
100
A s pa rti c Acid
1.92
2.20
2.40
Threonine
0.32
0.34
0.32
Serine
0.56
0.48
0.48
Asparagine
7.21
9.41
8.31
Glutamic Acid
3.11
2.45
3.11
Glutamine
3.27
4.00
3.01
Pro! in e
0. 40
0.52
0.53
Glycine
0.07
0.07
0.07
Alanine
0.18
0.19
0.18
Va li ne
1.51
1.54
1.35
Methionine
0.42
0.31
0.30
Is oleucine
0. 56
0.56
0.55
Leucine
0.31
0.36
0.34
Tyrosine
0.61
0.56
0.63
Phenylalanine
0.47
0.50
0.51
Lysine
0. 26
0.31
0.32
Histidine
0. 30
0.37
0.29
Arginine
1.00
0.59
0.91
y-Aminobutyric Acid
1.12
0.98
1.22
23.60
25.74
24.83
9.1%
5.2%
Total
Percent Increase
37
Table 1 . 2 .
The e f f e c t o f MgSO. f e r t i l i z a t i o n on the t o t a l (hydrolyzed)
amino acid content (mg/g D.W.) o f Katahdin potato tubers
(Year 1 ) .
MgSO^ ( l b s / A c r e )
0
40
100
19.10
21.47
21.02
Threonine
2.82
3.17
3.43
Seri ne
3.53
3.97
3.82
13.68
14.15
13.82
Proline
2. 68
3.41
3.32
Glycine
2.55
2.97
3.12
Alanine
2.72
3.20
3.32
Va lin e
4.53
5.12
5.09
Methionine
1.58
1.52
1.65
I so le uci ne
2.77
3.22
3.33
Leucine
4. 86
5.65
5.75
Tyrosine
2.25
2.53
2.73
Pihenylalanine
3.11
3.79
3.51
Lysine
4.54
5.43
5.46
Histidine
1.65
1.91
1.97
Argin ine
3.79
4.49
4.35
Y-Aminobutyric Acid
1.90
1.65
1.67
78.06
87.65
87.36
12.3%
11.9%
Amino Acids
A s p a r ti c Acid
Glutamic Acid
Total
Percent Increase
38
Minerals
There was no s i g n i f i c a n t e f f e c t o f magnesium f e r t i l i z a t i o n on the
t ub er contents o f potassium or phosphorus during the t hr ee years of
study.
Calcium content was s i g n i f i c a n t l y increased during years 1 and
3 , and magnesium content during a l l
t h r ee years (Table 1 . 3 ) .
An
increase in magnesium content of potato tubers fo ll o w in g MgSO^
a p p l i c a t i o n is in agreement with Vermes e t a l . ( 1 97 4 ).
Palaniyandi and
Smith (1978) found an increase in magnesium content o f t o t a l
pl ant s during two experiments, y e t the t o t a l
reduced in only one experiment.
snap bean
p l a n t potassium content was
Laughlin (1966) found no e f f e c t of
MgSO^ on the potassium, calcium or magnesium content o f potato t ub er s,
w h il e the phosphorus content was i n c o n s i s t e n t l y depressed.
However,
l e v e l s o f f e r t i l i z a t i o n were very high (250 and 500 l b / a c r e ) .
There was no s i g n i f i c a n t e f f e c t o f magnesium a p p l i c a t i o n on the
t u b e r contents o f boron or zinc during the t hr ee years o f study, and
manganese content was i n c o n s i s t e n t l y a f f e c t e d .
Cobalt and copper
contents were s i g n i f i c a n t l y increased during years 1 and 2 , and iron
content during a l l
t hr ee years (Table 1 . 4 ) .
An increase in iron content
o f tubers is n u t r i t i o n a l l y important since iro n de f i c ie n c y is probably
the most pr ev a le n t d e f i c i e n c y s t a t e a f f e c t i n g human p op ul at io ns , and i t
is g e n e r a ll y higher in developing co un tri es where the population r e l i e s
h e a v i l y on vegetable
1977).
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41
Firmness
Because o f r e s u l t s found f o r calcium and magnesium co n te n t,
firmness was determined during ye a r 3 o f the study.
fe rtiliza tio n
Magnesium
r e s u l t e d in tubers which e x h i b i t e d s i g n i f i c a n t l y
(p < 0 . 0 1 ) less deformation than c o n tr ol s in response to pressure
t e s t i n g (F ig ur e 1 . 1 2 ) .
Since r e si st an ce o f raw tuber t is s u e to a
pressure fo rce is s i g n i f i c a n t l y c o r r e l a t e d with s p e c i f i c g r a v i t y and
t e x t u r e (Lujan and Smith, 196 4) , a f i r m e r potato suggests a m e a l ie r
t e x t u r e and is associated with b e t t e r baking and processing q u a l i t i e s .
A f i r m e r potato is also less sus cep tib le to bru is in g and enzymatic
darkening.
An e l e v a t i o n in the calcium and magnesium content o f f e r t i l i z e d
tubers (Table 1 . 3 ) may be r e l a t e d to the f i r m e r t e x t u r e since the
presence of both elements in c e l l w a ll s has been associated w it h metal
bridges between pec tin molecules, and a f i r m e r t e x t u r e in cooked tubers
(Bartolome and H o f f , 1972).
Summary
Magnesium f e r t i l i z a t i o n
total
increased y i e l d , crude l i p i d ,
phospholipid,
n i tr o g e n , p r o t e i n , amino a c id s, calcium, magnesium, c o b a l t ,
copper, iron co n te n t, and firmness o f potato tubers.
discolored less and were lower in t o t a l
Tubers also
phenolic content than c o n tr ol s.
potato
tubers
(Year
3)
DEFORMATION
42
‘ LULU
•I—
LU
CD
43
Conclusion
Magnesium f e r t i l i z a t i o n
improved the chemical q u a l i t y o f potatoes
by a f f e c t i n g tuber d i s c o l o r a t i o n .
Black spot or enzymatic d i s c o l o r a t i o n
has been recognized as one o f the most important tub er defects in the
United St at es , r e s u l t i n g in s i g n i f i c a n t y e a r l y economic losses f o r
producers, processors and r e t a i l e r s .
Since magnesium f e r t i l i z a t i o n
re s u l t e d in potatoes which di scolored much less than c o n t r o l s , the
a p p l i c a t i o n of magnesium s u l f a t e to potato plants is one way by which
b e t t e r q u a l i t y tubers can be produced, and g r e a t e r economic ret ur ns can
be r e a l i z e d .
Magnesium a p p l i c a t i o n also a f f e c t e d the n u t r i t i v e value of
potatoes.
An increase in the content of nitrogenous c o n s ti t u e n t s and
minerals as a r e s u l t o f magnesium f e r t i l i z a t i o n
nutritional
is important from a
standpoint since potatoes contain high q u a l i t y p r o t e i n and
are a r e l a t i v e l y good source of many e s s e n t ia l min er als .
However,
potatoes are g e n e r a l l y not consumed in the United States f o r t h e i r
pr o t e i n or mineral
content since a v a r i e t y o f other f o o d s t u f fs o f higher
n u t r i e n t density are a v a i l a b l e and eaten.
In c o n t r a s t ,
in various t h i r d
world countries and under-developed nations where both c a l o r i e and
p r o t e i n m a l n u t r i t i o n are q u i t e p r e v e l a n t , many people r e l y h e a v il y on
staples such as potatoes f o r a su b s ta n ti a l
nu tritio n .
portion of t h e i r d a i l y
I t is thus the people of these nations who could r e a l l y reap
the maximum b e n e f i t s from crop f e r t i l i z a t i o n with magnesium.
Alth ou gh t h e a p p l i c a t i o n o f magnesium s u l f a t e improved both the
chemical and n u t r i t i v e v a l u e o f p o t a t o e s , these r e s u l t s
s p e c i f i c c l i m a t i c and c u l t u r a l
r e f l e c t th e
c o n d i t i o n accompanying t h i s
study.
Of
44
p a r t i c u l a r i n t e r e s t is t h a t s o i l s used in the study were adequate in
magnesium, and t h a t the e f f e c t s r e s u l t i n g from magnesium f e r t i l i z a t i o n
o f d e f i c i e n t s o i l s might be q u i t e d i f f e r e n t from those found here.
SPROUTING STUDY
I n t r o d u c t io n
Sprouting markedly reduces the a c c e p t a b i l i t y o f f re sh potatoes as
food.
In a d d i t i o n to being s h r i v e l e d and e x h i b i t i n g weight lo s s ,
sprouted tubers are h i g h l y susc ept ib le to b r u i s i n g .
Termination o f dormancy in the potato is a natural
r e s u l t s in the formation of sprouts.
phenomenon which
I t g e n e r a ll y occurs in stored
tubers when storage periods exceed two or more months, y e t exact
sprouting dates vary w it h v a r i e t y and storage con di tio ns .
Although both potato processors and consumers de s ir e a s p r o u t - f r e e
product, prevention o f sprout growth is o f te n d i f f i c u l t .
Many physical
and chemical f a c t o r s are known to end dormancy, whereas others are
employed to maintain dormancy and prevent sprouting.
breaking of dormancy is s t i l l
Relatively l i t t l e
However, the
a poorly understood phenomenon.
is known concerning the chemical composition o f the
sprouts and tu ber during sprouting.
Changes occurring during sprouting
may help to b e t t e r understand dormancy and what can be done in order to
maintain i t .
Sprouting may also a f f e c t the n u t r i t i o n a l q u a l i t y o f the tuber.
During sprouting n u t r i e n t s may be tr a n s l o c a t e d from the tuber to the
sprouts.
Since the potato is a va lu ab le source o f high q u a l i t y pr otein
(K al dy , 1972) and minerals (True e t a l . ,
197 8), changes r e s u l t i n g from
sprouting are important from a n u t r i t i o n a l
phy siological
one.
45
standpoint as well as a
46
Sprouting and Potato Physiology
Treadway e t a l . (1949) found t h a t the sprouts of potato tubers were
higher in reducing sugars and lower in starch than the whole potato, and
Mondy and Mattick (1969) observed t h a t potato sprouts contained s i g n i f i ­
c an tl y more crude l i p i d and phospholipid than e i t h e r the cortex or pith
sections of the tuber.
Sprouting is also associated with increased
r e s p i r a t io n (Burton e t a l . , 1955) and amylase a c t i v i t y (Bruinsma, 1962).
Although Cotrufo (1958) found no large changes in amino acid content of
the in te rn al tissues of potatoes at the breaking of the r e s t period,
Ashford and L e v i t t (1965) observed t h a t the r a t i o of protein to non­
p ro te in nitrogen was higher in the cortex than in the p i th tissu e both
a t 3°C and 26°C storage.
During sprouting p r o lin e is translocated from
the tuber to the sprout, and proline content is lower in sprouts and
tubers exposed to the l i g h t ( D i n k e l , 1968).
Following the normal rest period of potatoes there is a time when
the tubers nitrogenous reserves are e s s e n t i a l l y unavailable to support
shoot growth in the l i g h t , however, as the tubers age p h y s io lo g i c a l l y ,
they support increasing amounts of growth in the l i g h t , i n d ic a t in g a
gradual release of nitrogenous compounds f o r shoot growth in the l i g h t
( D i n k e l , 1968).
In a d d it io n , in senile tubers which have l o s t t h e i r
sprouting capacity the g i b b e r e l l i n content was found to be low, y et
exposure of these tubers to di ffuse da y lig h t f o r about a month resulted
in a large increase in g i b b e r e l l i n content as well as a recovery of
sprouting capacity (Bruinsma, 1962).
Rappaport and Smith (1962) found
t h a t the g i b b e r e l l i n content of sprouting potato tubers was 30 - f o ld
47
higher than in dormant tu be rs , and i t has r ece ntl y been observed th at
g i b b e r e l l i c acid produces changes in concentrations of ions and in
p l a s t i d morphology in dwarf corn plants (Neumann and Janossy, 1980).
This study was undertaken in order to i n ve st ig at e changes in
nitrogenous constituents and mineral composition of potato tubers and
sprouts following germination at room temperature in the l i g h t and dark.
Mate rials and Methods
Potatoes grown at the Cornell Vegetable Research Farm at Riverhead,
Long Isla nd , were used in the study.
f o r 6 months p r i o r to germination.
The potatoes were stored a t 5°C
Groups of twenty potatoes of the
clone NY 61, and the v a r i e t i e s Katahdin and Kennebec were allowed to
germinate at room temperature (21°C) f o r one month.
One-half of each
group of twenty tubers were germinated in the dark, while the other h a l f
were exposed to 100 f t .
the four week period.
candles of flourescent l i g h t continuously f o r
The e n t i r e sprouts were removed, cut into small
pieces, frozen, l y o p h i l i e d in a Stokes f r e e z e - d r y e r , and ground in a
Wiley m il l through a 40-mesh screen.
The potatoes were separated into
cortex and pith sections and prepared in the same manner.
Control
groups consisting of ten tubers of each v a r i e t y were taken d i r e c t l y from
storage and prepared in the same manner.
The determinations of t o t a l and non-protein nitrogen, p r o t e i n ,
t o t a l amino acids and minerals were made according to methods previously
described in the general experimental procedure chapter.
48
Results and Discussion
Total Nitrogen, Non-Protein Nitrogen and
Protein Content of Tubers
Al l v a r i e t i e s decreased in protein content in both cortex and pith
tissues of sprouted tubers as compared to unsprouted controls.
There
were no consistent changes in t o t a l and non-protein nitrogen content of
cortex and pi th tissues o f potato tubers following germination in e i t h e r
the l i g h t or dark fo r a l l
three v a r i e t i e s (Tables 2 . 1 - 2 . 3 ) .
Szalai and
Devay (1957) also found t h a t sprouting is associated with protein
hydrolysis in tubers.
Inconsistent changes in t o t a l and non-protein nitrogen may be due
to tuber v a r i a t i o n as well as f lu c tu a ti on s in re s p i r a t o r y losses of
carbohydrates resul ting from sprouting, but differences can be
eliminated i f values are expressed as nitrogen r a t i o s (Ashford and
Levitt,
1955).
When changes in nitrogen are expressed as the r a t i o of
protein N/non-protein N, cortex tissu e of a l l three v a r i e t i e s
demonstrated reduced nitrogen r a t io s following sprouting in both the
l i g h t and dark (Fig. 2 . 1 ) .
Katahdin and Kennebec p i t h tissue also
demonstrated the same trend, however, NY 61 pi th tissue had a higher
r a t i o following germination in the l i g h t (Fig. 2 . 2 ) .
Total Nitrogen, Non-Protein Nitrogen and
Protein Content of Sprouts
Both t o t a l
and non-protein nitrogen content of sprouts were
s i g n i f i c a n t l y (p < 0.01) increased over both the cortex and pith tissues
in a l l
three v a r i e t i e s (Figs. 2.3 and 2 . 4 ) , and protein content was 2-3
49
Table 2 . 1 .
The e f f e c t o f ge r m in a ti o n in the l i g h t and dark on the t o t a l
n i t r o g e n , n o n - p r o t e i n n i t r o g e n and p r o t e i n con ten ts o f
c o r t e x , p i t h and s p r o u t t i s s u e s o f NY 61 po ta to es .
Total N
(mg/g D.W.)
3
Non-Protein N
( mg/g D.W.)
Protein
(% D.W.)
Control
13.46 ± .21
4.25 ± .06
6.91
2.17
Dark
13.76 ± .03
5.30 ± .10
6.35
1.60
Light
12.66 ± .06
4.31 ± .02
6.26
1.94
Control
16.48 ± .06
7.74 ± .29
6.56
1.13
Dark
16.17 ± .13
8.02 ± .01
6.11
1.02
Light
14.38 ± .30
6.59 ± .01
5.84
1.18
Dark
45.02 ± 1.77
25.36 ± .62
14.75
00
Light
38.36 ± 1.77
17.22 ± .13
15.86
1.23
a
Protein N
NPN
Cortex
Pith
Sprouts
a. Values presented as an average o f 2 values ± S.D.
50
Table 2 . 2 .
The e f f e c t o f ger m ina ti on in the l i g h t and dark on the t o t a l
n i t r o g e n , n o n -p ro t e i n n i t r o g e n and p r o t e i n c on t e n t s o f
c o r t e x , p i t h and s p r o u t t i s s u e s o f Katahdin p o t a t o e s .
Total Na
(mg/g D.W.)
Non-Protein Na
(mg/g D.W.)
Protein
( % D.W.)
Protein N
NPN
Cortex
Control
19.48 ±
.06
10.14 ± .01
7.01
.92
Dark
17.37 ±
.23
9.83 ± .12
5.66
.77
Light
18.61 ±
.16
10.52 ± .01
6.07
.77
.28
14.99 ± .03
6.47
.58
Dark
23.57 +
20.67 0
.53
14.09 ±
O
o
4.94
.47
Light
24.39 ±
.26
16.82 ± .01
5.68
.45
Dark
39.69 ±
.28
20.44 ± .06
14.44
.94
Light
39.98 ± 1.47
17.99 ± .21
16.49
1.22
Pith
Control
•
Sprouts
a. Values presented as an average o f 2 values ± S.D.
51
Table 2 . 3 .
The e f f e c t o f ger m in a ti on in the l i g h t and dark on the t o t a l
n i t r o g e n , n o n - p r o t e i n n i t r o g e n and p r o t e i n c on te nt s o f
c o r t e x , p i t h and s pr ou t t i s s u e s o f Kennebec pot at oes .
Total Na
(mg/g D.W.)
Non-Protein Na
(mg/g D.W.)
Protein
(%D.W.)
Protein N
NPN
Control
15.11 ± .17
6.96 ± .09
6.11
1.17
Dark
15.26 ± .08
7.47 ± .01
5.84
1.04
Light
13.89 ± .00
6.63 ± .11
5.45
1.10
Control
16.36 ± .47
8.72 ± .04
5.73
.88
Dark
16.00 ± .26
9.62 ± .21
4.79
.66
Light
15.48 ± .14
9.42 ± .09
4.55
.64
Dark
41.26 ± .17
20.47 ± .62
15.59
1.02
Light
48.42 ± .38
16.71 ± .94
16.28
1.30
Cortex
Pith
Sprouts
a. Values presented as an average o f 2 values ± S.D.
52
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times higher in the sprouts ( F i g . 2 . 5 ) .
Ashford and L e v i t t (1965)
suggest t h a t the r a t i o o f p r o t e i n / n o n - p r o t e i n nitrogen be considered a
measure of the p r o t e i n syn thesizing p o t e n t i a l of the t i s s u e , thus the
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pr o t e i n in order to make amino acids a v a i l a b l e f o r t r a n s l o c a t i o n to the
growing sprout t i s s u e .
E f f e c t of Li gh t on Nitrogenous Constituents
Although a comparison of dark and l i g h t germinated tubers in di c at es
no con sistent d i f f e r e n c e s in e i t h e r cortex or p i th p r o t e i n / n o n - p r o t e i n
nitrogen r a t i o s ( F ig s .
2.1 and 2 . 2 ) , a comparison of the sprouts from
the l i g h t and dark exposed tubers i n d ic a t e s a much higher r a t i o in the
l i g h t exposed sprouts ( F i g . 2 . 6 ) .
Zucker (1963) found t h a t disks of
pulp tiss ue from potato tubers increased in pr ot ei n content when exposed
to i l l u m i n a t i o n , and t h a t continuous i l l u m i n a t i o n g r e a t l y increased the
synthesis of pro te in s and led to greening and c h l o r o p l a s t development in
the disks.
The higher pr ot ei n N/no n -p ro te in N r a t i o observed f o r the
l i g h t exposed sprouts may be due to a s i m i l a r kind of s t i m u l a t i o n in the
m e t a b o l i c a l l y a c t i v e sprout t i s s u e .
Total Amino Acid Content of Tubers
The e f f e c t of germination in the l i g h t and dark on the t o t a l
(hydrolyzed) amino acid contents of the cortex t is s ue of the three
potato v a r i e t i e s is i n di c at ed in Table 2 . 4 .
Sprouting in the l i g h t or
dark did not show co n sis ten t pat terns f o r in d iv id u a l
amino acids or
57
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59
60
t o t a l amino acid content between v a r i e t i e s .
The t o t a l amino acid
content o f NY 61 and Katahdin cortex t is s u e were s l i g h t l y reduced
fo l l o w i n g germinatino in both the l i g h t and dark, wh ile the t o t a l amino
acid content of Kennebec cortex tiss ue was s l i g h t l y increased in the
dark and decreased in the l i g h t .
were not g r ea t ( 0 . 5 - 9 . 0 % ) .
In a l l
cases, however, d i f f e r e n c e s
Cotrufo (1958) did not f i n d any la rg e
changes in amino acid content o f potatoes a t the breaking o f the r e s t
pe ri od .
Total Amino Acid Content o f Sprouts
The e f f e c t of germination in the l i g h t and dark on the t o t a l amino
acid contents of the sprouts of the t hr ee potato v a r i e t i e s
in Table 2 . 5 .
is in d ic a t e d •
The t o t a l amino acid content o f MY 61 sprouts was de­
creased in l i g h t exposed t u b e r s , while l i g h t exposed Katahdin and
Kennebec sprouts had a higher t o t a l amino acid content than dark g e r ­
minated sprouts.
A comparison of the t o t a l
amino acid content o f the sprouts (Table
2 . 5 ) with t h a t of the cortex t is s u e (Table 2 . 4 ) i n d ic at es t h a t in a l l
cases the sprouts were much higher in t o t a l amino acids.
The most
s t r i k i n g increase was in the content of p r o l i n e , which was 5-8 times
higher in the sprouts.
Steward et a l . (1958) observed t h a t hydroxy-
p r o l i n e c o n s is t e n t l y appeared as a more conspicious amino acid in the
pr ot ei n o f p r o l i f e r a t i n g potato cortex and c a r r o t root phloem c e l l s than
in the p r o t e i n of the c e l l s from which the t is s u e c u l t u r e was de ri ve d,
and Breyhan e t a l .
(1959) found t h a t p r o l i n e is t ra ns lo ca te d from the
tuber to the sprouts during germination.
Although Breyhan e t a l .
61
Tab le 2 . 5 .
The e f f e c t o f g e r m i n a t i o n i n t h e l i g h t and da rk on t h e t o t a l
( h y d r o l y z e d ) amino a c i d c o n t e n t s (mg/g D.W.) o f p o t a t o
sprouts.
Katahdin
NY 61
As p a r ti c Acid
Kennebec
Dark
Light
Dark
Light
Dark
Li ght
45.21
27.96
38.86
26.13
34.09
27.52
Threonine
5.42
5. 14
4.52
5.55
4.65
5.68
Serine
7.08
6. 33
5.93
6.76
6.01
7.06
Glutamic Acid
25.72
21.37
17.53
18.00
20.95
21.10
Proline
25.81
25.59
15.55
22.57
19.05
23.76
Glycine
5. 99
6.31
5. 54
5.48
4. 63
7.25
Alanine
7.35
6.53
6. 19
6.14
5. 54
8.01
10.04
8. 45
9.03
9.05
8.90
10.02
Methionine
2.90
2.68
2.65
2.88
2.68
3.15
I s o le u ci n e
6.21
5.47
6.02
6.25
5.73
6.65
Leucine
9.83
9.67
9.19
10.63
9.33
11.78
Tryosine
3.94
3.36
3.80
3.57
3.23
4.22
Phenylalanine
5.14
5.15
4. 56
5.65
4.80
6.2 0
10.53
10.24
10.19
12.32
10.05
12.49
Histidine
2.97
3.13
2.97
3.16
2.73
3.58
Ar ginine
7. 60
6.93
6. 73
6.89
6. 99
7.03
y-Aminobutyric Acid
3.09
4.36
2.43
2.87
3.05
4.22
V a lin e
Lysine
Total
184.8
158.6
151.7
191.7
152.4
169.7
62
(1959) found t h a t the p r o l i n e content was highe r in sprouts exposed to
the l i g h t ,
in t h i s study the p r o l in e content was higher in the sprouts
o f l i g h t exposed Katahdin and Kennebec t u b e r s , y e t was not d i f f e r e n t in
NY 61 sprouts.
Breyhan et a l .
(1959) suggests t h a t p r o l i n e is a pre­
cursor o f c h l o r o p h y l l , and t h a t a f t e r the r e s t period p r o l i n e is a c t i ­
vated and t ra nsported to the growing po in t where i t
is combined w ith
g l y c i n e m e t a b o l i c a l l y obtained from ser in e f o r the formation of green
pigments.
However, the unusual presence o f p r o l i n e in p l a n t c e l l
tumors, as well as in the p r o t e i n f r a c t i o n o f r a p i d l y d i v i d i n g c e l l s of
various p l a n t - t i s s u e c u l t u r e s
tional
(Steward e t a l . ,
1958) suggests an a d d i ­
or a l t e r n a t e r o l e f o r t h i s amino a ci d .
Mineral Composition
The e f f e c t o f germination in the l i g h t and dark on the mineral
composition of potato tu ber t is s u e and sprouts i s given in Tables
and 2 . 7 .
The sprouts o f a l l
v a r i e t i e s were s i g n i f i c a n t l y
2.6
(p < 0 . 0 1 )
higher in copper, z i n c , magnesium, and phosphorus contents than cortex
or p i t h tissues independent o f l i g h t or dark exposure.
The boron
content o f sprouts was also s i g n i f i c a n t l y (p < 0 . 0 1 ) higher then e i t h e r
cort ex or p i th tiss ues in both the Kennebec and NY 61 v a r i e t i e s . L e v i t t and Todd (1952) found t h a t i r o n , copper and zinc were
associated with the p r o t e i n f r a c t i o n o f potato t is s u e as m e t a l - p r o t e i n
complexes, and t h a t no s i g n i f i c a n t d i f f e r e n c e s in the d i s t r i b u t i o n of
i r o n , copper or zinc in the proteins could be detected during the
t r a n s i t i o n from dormancy to growth.
The high copper and zinc contents
in the sprout t is s u e may th e r e f o r e be associated with the high pr o t e i n
63
Table 2 . 6 .
The e f f e c t of germination in the l i g h t and dark on the
macromineral composition (% D.W.) o f c o r t e x , p i t h and
sprout tiss ues o f potatoes.
K
NY 61
Cx Control
Dark
Li ght
PI
Control
Dark
Light
P
Ca
Mg
3.07 + .06
3.31 ± .13
2.87 ± .57
.336 + .048
.359 + .003
.339 ± .003
.035 ± .000
.039 + .005
.038 ± .004
.101 ± .001
.105 ± .001
.095 ± .003
.02
.04
.05
.340 ± .015
.362 ± .025
.327 ± .015
.021 + .000
.021 ± .001
.023 + .004
.107 ± .001
.114 ± .005
.107 ± .005
.02
.12
.785 ± .002
.727 ± .010
.034 ± .000
.035 + .000
.206 ± .001
.198 + .001
.03
.01
.03
.375 + .001
.358 ± .004
.370 ± .002
.035 ± .002
.043 ± .006
.044 ± .007
.109 + .001
.106 ± .001
.105 ± .001
1.54 ± .02
2.60 ± .15
2.71 ± .07
.381 ± .005
.354 ± .002
.381 + .002
.025 ± .006
.027 + .001
.038 ± .001
.103
.104
.111
2.50
2.68
2.57
SPR Dark
Light
2.67
2.49
Katahdin
Cx Control
Dark
Li ght
2.58
2.55
2.60
PI
Control
Dark
Light
±
±
±
±
±
±
±
±
±
±
±
.000
.000
.000
SPR Dark
Light
2.31
2.67
.07
.57
.733 ± .004
.743 + .015
.029 + .001
.031 + .001
.195 ± .001
.216 ± .004
Kennebec
Cx Control
Dark
Light
2.11 ± .02
2.20 ± .02
2.31 + .26
.321 ± .006
.320 ± .004
.347 ± .019
.038 ± .000
.038 + .001
.037 ± .002
.112 X .002
.109 ± .001
.106 4- .006
1.99 + .15
1.87 ± .06
2.03 ± .18
.318 + .004
.312 + .005
.320 ± .004
.019 ± .004
.022 + .000
.022 + .007
.097 ± .002
.095 ± .001
.105 + .006
2.27 ± .17
2.14 + .09
.759
.721
.036 ± .001
.035 ± .001
.198 ± .005
.204 ± .006
PI
Control
Dark
Li ght
SPR Dark
Li ght
±
±
±
±
.019
.029
Values presented as an average of 2 values ± S.D.
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2.7.
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65
content of the sprouts.
Although the i ro n content of the sprouts was
not c o n s i s t e n t l y higher than t h a t o f the o th er tuber t i s s u e s , in a l l
cases tu ber cortex t i s s u e was s i g n i f i c a n t l y
(p < 0 . 0 1 ) highe r in iron
content than the p i t h t i s s u e , and the i ro n content o f the sprouts more
c l o s e l y approximated t h a t o f the co r t e x .
Magnesium content of the sprouts was also s i g n i f i c a n t l y higher than
e i t h e r the cortex or p i t h tissues f o r a l l
t h r ee v a r i e t i e s .
requirement f o r magnesium during the a c t i v a t i o n ,
The
i n i t i a t i o n and
elonga tio n steps o f p r o t e i n syn the sis , as well as i t s involvement in
l i p i d synthesis suggests t h a t magnesium may be associated w ith both the
p r o t e i n and l i p i d contents o f the sprouts.
The s i g n i f i c a n t l y
(p < 0 .0 1)
higher magnesium content o f the l i g h t exposed cortex and p i t h tis s ue s of
Katahdin tubers (Table 2 . 6 ) may i n d i c a t e a higher chlor oph yll production
as a r e s u l t of l i g h t exposure in t h a t p a r t i c u l a r v a r i e t y .
However,
chl or oph yll content was not assessed.
Mondy and M a t t i c k (1969) found t h a t the sprouts from potato tubers
were s i g n i f i c a n t l y higher in crude l i p i d and phospholipid contents than
e i t h e r cortex or p i t h t i s s u e s .
Potatoes t r e a t e d with boron were also
s i g n i f i c a n t l y higher in crude l i p i d and phospholipid content than
untr eat ed con tro ls (Mondy e t a l . ,
1965).
Thus, the higher phosphorus
and boron contents of sprout tiss ue may be associated with the l i p i d
m aterial.
Summary
In a l l
v a r i e t i e s the sprouts were s i g n i f i c a n t l y (p < 0 . 0 1 ) higher
than e i t h e r cortex or p i t h t iss ue in t o t a l
and non-protein n i tr o g e n .
66
Protei n and t o t a l
amino acid content were highest in sprout t is s u e .
Sprout t is s u e was also s i g n i f i c a n t l y (p < 0 . 0 1 ) higher in copper, z i n c ,
magnesium, and phosphorus.
In the sprouts exposed to l i g h t the r a t i o of
p r o t e i n / n o n - p r o t e i n nitrogen was higher than those in the dark.
Conclusion
The high contents o f nitrogenous c on st it ue nt s and se le ct ed minerals
in the sprouts o f potato tubers suggests t h a t dormancy may be prolonged
by the use o f compounds t h a t i n h i b i t the t r a n s l o c a t i o n o f amino acids
i n t o the sprouts, or in some o th er way i n t e r f e r e wit h p r o t e i n synthesis;
o r by substances t h a t i n t e r f e r e w ith e i t h e r the t r a n s l o c a t i o n or balance
o f es s en tia l m in e r a ls .
Although sprout t is s u e was found to be
considerably higher in nitrogenous co n st it u en t s and selec ted minerals as
compared to cortex and p i t h t i s s u e s , the higher n u t r i e n t contents in the
sprouts did not lead to larg e n u t r i e n t reductions in e i t h e r the cortex
or p i t h tis su es of the tuber.
Sprouting th e r e f o r e does not r e s u l t in
tuber t is s u e with severely reduced p r o t e i n and mineral contents and may
not be a gr eat n u t r i t i o n a l
nutrients.
importance wit h regard to these p a r t i c u l a r
SPROUT INHIBITOR STUDY
I n t r o d u c t io n
Sprouting markedly reduces the q u a l i t y of f re sh potatoes due to
s h r i v e l i n g and weight l o ss , thus l a r g e sums of money are spent annually
to prevent sprouting of stored potato tubers.
Chemical sprout
i n h i b i t o r s have received considerable acceptance in the United States
since becoming commercially a v a i l a b l e in 1947.
Maleic hydrazide (MH)
and i s o p r o p y l - N - ( 3 - c h l o r o p h e n y l ) carbamate (CIPC) are two such chemical
i n h i b i t o r s of sprouting.
Since potatoes are commercially produced in
every s t a t e in the United States and are considered a major vegetable
crop (Smith, 1 9 7 7) , tubers are f r e q u e n t l y t r e a t e d w ith MH or CIPC in an
attempt to maintain q u a l i t y and economic r e t u r n .
This study deals with
the e f f e c t of MH and CIPC on the chemical q u a l i t y of potatoes.
I.
Maleic Hydrazide
Maleic hydrazide (MH; 1 , 2 - d i h y d r o - 3 ,6 p y r i d a z i n e - d io n e )
is used in
a g r i c u l t u r e in order to suppress sprouting of vegetables and stored food
crops, control
sucker growth in tobacco plants and r e t a r d flow er ing
( S w ie t l in s k a and Zuk, 1978).
Since i t
is only s l i g h t l y soluble in water
(0.4% a t 2 0 ° C ), i t s diethanolamine and sodium s a l t s are commonly used
for agricultural
purposes.
Its structural
formula is as follows:
68
Maleic hydrazide was f i r s t recognized as a unique growth re gulant
in 1949 (Schoene and Hoffman, 1949).
Subsequently, i t was shown t h a t
preharvest f o l i a r sprays o f MH could induce a s t r i k i n g i n h i b i t i o n of
sprouting and g r e a t l y reduce storage losses in onions (Wittwer and
Sharma, 1 9 5 0 ) , ca r r ot s (Wit twe r e t a l . , 195 0) , sugar beets (Wi ttwer and
Hansen, 1951) and potatoes ( Pat te rs on e t a l . ,
1952).
Numerous other
studies have i n v e s t i g a t e d the metabolism, mode of a ct io n and e f f e c t s of
MH in various p l a n t species, y e t few consistent conclusions have been
drawn.
Metabolism.
MH must be absorbed and t ra ns lo ca te d to growing pl an t
tissues in order to be e f f e c t i v e .
It
is st abl e and n o n v o l a t i l e , y e t
absorption r a t e depends p r i n c i p a l l y upon pl an t species and co n di tio n.
High r e l a t i v e humidity w i l l
increase absorption, and the diethanolamine
formu lation (MH-30) is most e f f i c i e n t l y absorbed (Smith e t a l . ,
1959).
MH is a c t i v e l y accumulated in roots and other p l a n t p a r t s , and is f a i r l y
stable (Nooden, 1970).
absorbed [ ^ C ]
Frear and Swanson (1978) found t h a t f o l i a r
MH was t r a n s l o c a t e d r a p i d l y to a c t i v e l y growing tissues
of tobacco plants in a 1s o u r c e - t o - s i n k 1 p a t t e r n , and 28 days a f t e r
treatment 30-40% of the absorbed MH was t r a ns lo ca t ed to the roots and
released i n t o the n u t r i e n t s o l u t i o n , 12-22% remained in the p l a n t ,
14-18% was e x t r a c t e d as methanol-soluble m e t a b o l it e s , and 25-35%
remained in the roots and o th er tiss ues as a methanol
ins ol ubl e residue.
Towers e t a l . (1958) found t h a t 15% of l a b e l l e d MH a p p lie d to young
wheat leaves formed a g- gl uco si de, and Frear and Swanson (1978) observed
t h a t 90% o f the methanol soluble p o l a r metabolites e x t r a c t e d from four
v a r i e t i e s of tobacco plants was also the g-glucoside.
69
Physiological e f f e c t s .
Tubers under the i n f l u e n c e of MH had a reduced
monosaccharide con ten t, increased starch co n te n t, changes in the r a t i o
of d i f f e r e n t phosphorus f r a c t i o n s , and considerable s h i f t s in the
a c t i v i t y o f enzymes o f carbohydrate metabolism ( R a k i t i n et a l . ,
1971).
Maleic hydrazide sol ution s also lowered the RNA content in potato buds,
depressed i nc or por at io n o f [ 8 - 14C] adenine in RNA, and stimulated
i n co r po r at io n o f [
1978).
14
C] le uci ne i n t o p ro te in of the buds ( R a k i t i n e t a l . ,
Schoene and Hoffmann (1949) found t h a t MH as well destroyed the
control which the stem apex o f tomato plants normally exerts on the
growth of l a t e r a l
buds ( a p i c a l
dominance), which is an auxin-mediated
phenomenon t h a t r e s u l t s in a bushy p l a n t .
Hormonal r e g u l a t i o n .
I t has been suggested t h a t maleic hydrazide
i n h i b i t s sprouting by f u n c t io n in g as an anti-hormonal
agent.
Leopold
and Klein (1952) showed t h a t MH and i n d o l e a c e t i c acid (auxin) are
competitive i n h i b i t o r s , wh ile Brian and Hemming (1957) found MH to a
g i b b e r e l l i n a nt ag o ni s t.
Neumann and Janossy (1980) found t h a t
g i b b e r e l l i c acid caused changes in ch l o r o p l a s t morphology of dwarf corn
p l a n t s , and Goncharik and Marshakova (1962) observed a dec lin e in both
pigmentation and i n t e n s i t y o f photosynthesis o f c hl or op la st s two weeks
a f t e r MH a p p l i c a t i o n .
Other researchers b e l i e v e t h a t maleic hydrazide
i n h i b i t s sprouting by blocking c e l l
d i v i s i o n and i n t e r f e r i n g with
nuc lei c acid metabolism, although c e l l extension is also a f f e c t e d .
Since auxins and g i b b e r e l l i n s help re gu la te both c e l l
d i v i s i o n and
elongation (Greulach, 197 3) , i t may be t h a t MH act io n is not s p e c i f i c to
a s i n g l e hormone, but t h a t hormonal re g u la t io n and MH action have common
f u nc t io na l
p r o p e rt ie s a t the biochemical l e v e l .
70
Membrane p e r m e a b i l i t y .
Although the mechanism o f hormonal a ct io n has
not been e l u c i d a t e d , Greulach (1973) reported t h a t auxin may ac t through
a d i r e c t e f f e c t on c e l l wa ll
of the plasma membrane.
components or by a f f e c t i n g the p e r m e a b il it y
Thimann and Samuel
(1955) suggested t h a t the
a c t i v i t y o f auxin on the elo ng at io n of p l a n t c e l l s occurs through i t s
in fl u e n c e on the c e l l w a l l .
A loosening o f c e l l w all
cons tituen ts
followe d by an osmotic uptake o f water is envisaged w ith a subsequent
elong at io n o f the c e l l .
Taylorson and Holm (1961) in v e s t i g a t e d maleic
hyd ra zid e -a u xi n i n t e r a c t i o n s in wa te r uptake o f potato discs.
They
found t h a t MH can negate the s t im u l a t o r y a ct io n o f auxin on water
uptake, and t h a t MH tends to accumulate in the s o l i d f r a c t i o n o f potato
d i s c s , suggesting an a f f i n i t y f o r c e r t a i n c e l l wall
c o n s ti t u e n t s .
Nooden also reported t h a t MH is bound to c e l l w a lls in corn roots by an
energy - r e q u i r i n g process, and S t . John and H i l t o n (1978) found t h a t
c e r t a i n herbici des can a l t e r membrane p e r m e a b il it y by a d i r e c t i n t e r ­
ac ti on on contact with membranes.
Wood and Pal eg (1974) furthermore
found t h a t g i b b e r e l l i c acid caused an increase in the p e r m e a b il it y o f
model membranes to e i t h e r charged or uncharged leakage i n d i c a t o r s , and
Neumann and Janossy (1980) observed t h a t g i b b e r e l l i c acid caused changes
in soluble ion content o f d i f f e r e n t c e l l u l a r compartments of maize
plants.
The hormone may thus a c t at the membrane le v e l since changes in
the p r o p e rt i e s of membrane p e r m e a b il it y can cause v a r i a t i o n s in ion
r a t i o s , followed by a c t i v a t i o n or i n h i b i t i o n of important enzyme sys­
tems.
Mineral ba la nc e.
d ifferential
The importance of proper i o n ic balance f o r normal
membrane p e r m e a b il it y and c e l l u l a r fu nc tio ni ng is well
71
e s t a b l i s h e d , as is the t o x i c i t y of c e r t a i n heavy metals and tr a c e
elements when present in excess.
Boron, copper, magnesium, manganese,
molybdenum and zinc may be t o x i c to plants when present in more than
usual t r a c e q u a n t i t i e s
(Greulach, 1973).
Greulach (1954) found t h a t a
complete mineral medium could p a r t i a l l y r e l i e v e the i n h i b i t o r y e f f e c t s
o f MH on germinating peas, w hi le Suda (1960) observed t h a t the a d d it io n
o f a t r a c e of heavy metals could reverse the MH-induced suppression of
auxin-induced growth o f Avena c o l e o p t i l e se c tio ns .
Kessler and Moscicki
(1958) found t h a t the a p p l i c a t i o n of MH to pl ant s promoted the bas ipe tal
t r a n s l o c a t i o n of calcium but not iron .
Potato tuber sprouts contain very high contents of nitrogenous
c o n s ti t u e n t s and se le ct ed minerals ( K l e in e t a l . ,
1981), thus sprout
i n h i b i t i o n may be p o t e n t i a t e d through the use compounds t h a t i n t e r f e r e
w it h p r o t e i n synthesis a t the growing p o i n t
or by compounds t h a t
i n t e r f e r e w it h the t r a n s l o c a t i o n or balance
of e s s e n t ia l
been reported to a l t e r p r o t e i n synthesis in
potato sprouts ( R a k i t i n e t
a l.,
however, the e f f e c t of
1978) and pea seedlings (Lobov, 1 9 8 1) ,
maleic hydrazide on the mineral
is thought t h a t a l t e r a t i o n s
composition
ions.
MH has
o f sprouts is unknown.
It
in prot ein synthesis as a r e s u l t of MH
a ct io n are due to p r i o r disturbances in nu c le ic acid metabolism.
The
manner by which maleic hydrazide creates such disturbances is unknown.
Since p l a n t growth r e g u l a t o r s (auxin and g i b b e r e l l i n s ) appear to a f f e c t
membrane p er m ea b ili t y and i o n i c d i s t r i b u t i o n , an i n v e s t i g a t i o n i n t o the
e f f e c t of MH on the mineral composition of potato sprout and tuber
t is s u e is of considerable i n t e r e s t .
72
II.
CIPC
CIPC (isopropyl N-3-chlorophenyl carbamate; chlorpropham) is
another sy n th e ti c growth r e g u l a t e r which is used to i n h i b i t sprouting of
potato t ub er s, although i t
is r e p r e s e n t a t i v e o f a d i f f e r e n t class of
economically important he r b ic id e s .
Its structural
formula is as
fo ll o w s :
0
\
C l
CIPC is very sol ubl e in organic s o l v e n ts , thus i t
is e a s i l y
compounded i n to l i q u i d e m u l s i f i a b l e for mu lation s which are r e a d i l y
v o l a t i l i z e d at high temperatures (Lee, 1969).
Sprout control can
t h e r e f o r e be achieved by t r e a t i n g harvested potato tubers with e i t h e r
vaporized CIPC or by dipping tubers in aqueous suspensions.
Foliar
a p p li c a t io n s have not proved e f f e c t i v e .
Physiological e f f e c t s .
Falgout (1965) observed the CIPC had l i t t l e
e f f e c t on reducing or non-reducing sugars, starch or dry m at ter content
or on r e s p i r a t i o n r a t e o f stored potato tubers.
C r a f t and Audia (1959)
found no e f f e c t on oxygen uptake in whole tubers or in potato s l i c e s
with CIPC.
Mann et a l . (1965) observed t h a t a c t i v e uptake of amino
acids was not i n h i b i t e d by CIPC, but t h a t CIPC treatment caused severe
i n h i b i t i o n of le ucine incorpo ratio n i n to pr o t e i n in segments o f pl an t
seed!ings.
73'
Mode of a c t i o n .
Phenyl carbamate-induced r e t a r d a t i o n and cessation of
p l a n t growth are p r i m a r i l y l in k ed with disturbances o f m it os is (Scot t
and Struckmeyer, 1955).
I t has been suggested t h a t phenyl carbamates
( l i k e c o l c h i c i n e ) fun ct io n by des troying the spindle apparatus, thereby
gi vi ng r i s e to anomalous m i t o t i c f i g u r e s and nuclear forms, X-shaped
pa ir s of chromosomes, m u l t i n u c l e a r i t y , and pol yploidy in c e l l s (Ennis,
1948; Doxey, 1949).
Lee (1969) observed chromosome c o n tr a c t i o n or
clumping in potato sprout t i p s t r e a t e d w ith CIPC.
The primary purpose o f t h i s i n v e s t i g a t i o n was to study the e f f e c t
o f maleic hydrazide treatment on nitrogenous c on st it ue nt s of potato
t ub er s, and on a l t e r a t i o n s and accumulation of minerals in tubers and
sprouts.
A comparison was also made with the e f f e c t s e l l i c i t e d by CIPC,
since MH and CIPC are the two most common and e f f e c t i v e commercially
used chemical
i n h i b i t o r s of sprouting.
M a t e r i a l s and Methods--Maleic Hydrazide
This study
be compared f o r
is divided i n to two parts so
t h a t the e f f e c t s of MH can
both unsprouted and sprouted t is s u es .
I - - T u b e r Tissue
Potatoes grown a t the Cornell Vegetable
Riverhead, Long
Research Farms a t
Isla nd and a t I t h a c a , NY were used in the study.
Nitrogen content and mineral composition were determined on the cortex
and pi th t i s s u e o f Katahdin potatoes grown on Long Isla nd and on
Katahdin and Kennebec tubers grown a t I t h a c a , during the 1980 growing
season (Year 1) f o l l o w in g a p p l i c a t i o n of maleic hydrazide a t 0 and 3
lbs/acre.
Nitrogen content was determined f o r the cortex t is s u e of
74
Katahdin potatoes grown on Long Isla nd during a previous growing season
(Year 2) f o l l o w i n g a p p l i c a t i o n o f maleic hydrazide at 0 , 3 , 6 and 9
l b s / a c r e , and mineral content was determined f o r the 0 and 9 l b / a c r e MH
tr e a t e d groups.
Potatoes were stored a t 5°C f o r 6 months p r i o r to
analysis.
I I — Sprout and Bud Tissue
Mineral
content was determined f o r bud and sprout t i s s u e of
Katahdin and Kennebec tubers grown a t Ithac a during the 1980 growing
season f o l l o w i n g a p p l i c a t i o n of maleic hydrazide a t 0 and 3 l b s / a c r e .
Tissues were analyzed at t hr ee d i f f e r e n t times (Time 0 , 1 and 2) in
order to compare the t r a n s l o c a t i o n and accumulation o f minerals
accompanying germination as a f f e c t e d by MH.
Time 0 tubers ( c o n t r o l )
consisted of 10 un treated and 10 MH t r e a t e d tubers o f each v a r i e t y taken
from storage a t 5°C f o r 6 months.
Analyses were made on bud t i s s u e ,
which consisted o f a 1 cm long X 14 mm wide c y l i n d r i c a l
a s t a i n le s s st eel
cork borer a t the apical eye.
section cut with
Time 1 tubers consisted
o f the same number o f t re a te d and untreated tubers taken from storage at
the same time but placed a t room temperature in the dark f o r 1 week, a t
which time the tubers were j u s t beginning to sprout.
on the bud t i s s u e .
Analyses were made
Time 2 tubers consisted of the same number of tubers
taken from storage a t the same time but placed at room temperature in
the dark f o r 1 month, a t which time the tubers were sprouted.
approximate length o f sprouts was as f o llo w s:
The
Untreated Kennebec
(10 mm), Kennebec + MH (4 mm), un treated Katahdin (30 mm), Katahdin + MH
(10 mm).
75
Each t is s u e ( c o r t e x , p i t h , bud and sprouts) was f r o z e n , l y o p h i l i z e d
in a Stokes f r e e z e - d r y e r , and ground in e i t h e r a Wiley m i l l through a 40
mesh screen or with a mortar and p e s t l e .
The nitrog en and mineral
determinat ions were made according to methods prev io us ly described in
the general experimental
procedures cha pter.
Du pli cat e determinations
were made on each tre at m e nt .
Results and Discussion
Total Nitrogen
In both years of the study the t o t a l
nitrog en content o f cortex
t is s u e o f tubers was s i g n i f i c a n t l y (p < 0 . 0 1 )
a p p l i c a t i o n o f MH (F ig s . 3.1 and 3 . 2 ) .
increased by the
Katahdin and Kennebec tubers
grown at Ithac a (Year 1) demonstrated an increased nitrogen content in
response to the a p p l i c a t i o n o f 3 l b / a c r e MH ( F i g . 3 . 1 , Appendix Table
2 . 1 ) , w hi le the a p p l i c a t i o n o f 6 and 9 l b s / a c r e MH r e s u l t e d in increases
in the t o t a l
nitrogen content o f Katahdin potatoes grown on Long Island
(Year 2 , Fig. 3 . 2 , Appendix Table 2 . 2 ) .
No co n sis ten t d i f f e r e n c e s were
observed f o r p i t h t i s s u e .
Non-Protein Nitrogen
The non-protein nitrog en content o f cortex t i s s u e of Katahdin and
Kennebec tubers grown a t Ithaca (Year 1) was s i g n i f i c a n t l y
increased by the a p p l i c a t i o n of MH at 3 l b / a c r e ( F i g .
Table 2 . 1 ) .
(p < 0 . 0 1 )
3 . 3 , Appendix
The a p p l i c a t i o n of 9 l b / a c r e MH s i g n i f i c a n t l y (p < 0 . 0 1 )
increased the non-protein nitrog en content o f Katahdin tubers grown on
C
M
04
T”
04
3.1.
O
M
a 6 /6 u i
Fig.
NITROGEN
Effect of 0 and 3 lbs/acre MH on the total nitrogen content of cortex
pith tissues from Katahdin potato tubers grown on L. I . , and Katahdin
Kennebec tubers grown at Ithaca (Year 1 ) .
TOTAL
and
and
76
C
M
*M ’C3 6/6lu
Fig.
3.2.
Effect
tissue
N ITR O G EN
of 0, 3, 6 and 9 lbs/acre MH on the total nitrogen content
from Katahdin potato tubers grown on L. I. (Year 2 . ) .
TOTAL
of
cort ex
77
m
a
6 '6uj
Fig.
3.3.
NITROGEN
Effect of 0 and 3 lbs/acre MH on the nonprotein nitrogen
and pith tissues from Katahdin potato tubers grown on L.
and Kennebec tubers grown at Ithaca (Year 1 ) .
NON-PROTEIN
content
I . , and
of cort ex
Katahdin
78
79
Long Is land (Year 2 , Fi g. 3 . 4 , Appendix Table 2 . 2 ) .
No con sis ten t
d i f f e r e n c e s were observed f o r p i t h t i s s u e .
Protein
The pr o t e i n content of cort ex t is s u e o f Katahdin and Kennebec
tubers grown during Year 1 was increased by the a p p l i c a t i o n o f MH a t
3 lb/acre
( F i g . 3 . 5 , Appendix Table 2 . 1 ) , however, the increases are
s l i g h t and probably o f l i t t l e
importance.
The pr o t e i n content o f cortex
t is s u e o f Katahdin tubers grown during Year 2 was not a f f e c t e d by the
a p p l i c a t i o n of MH a t 3 , 6 or 9 l b s / a c r e ( F i g . 3 . 6 , Appendix Table 2 . 2 ) .
No trend was found f o r p i t h t i s s u e .
Mineral Content of Tuber Tissues
The a p p l i c a t i o n o f MH a t 3 l b / a c r e (y ea r 1) did not c o n s i s t e n t l y
a l t e r the macromineral
(Table 3 . 1 ) or micromineral
(Table 3 . 2 ) content
o f cortex or p i th t i s s u e s , but in the second y e a r the phosphorus and
zi nc contents of cortex t is s u e were s i g n i f i c a n t l y (p < 0 . 0 1 )
increased
by 9 l b s / a c r e MH, and the calcium content was s i g n i f i c a n t l y (p < 0 . 0 1 )
reduced (Table 3 . 3 ) .
R a k i t i n e t a l . (1971) reported t h a t MH caused
considerable s h i f t s in the r a t i o of d i f f e r e n t phosphorus f r a c t i o n s .
Mineral Content of Apical
Bud and Sprouts
Maleic hydrazide did not a f f e c t the accumulation of e i t h e r
macrominerals (Table 3 . 4 ) or microminerals (Table 3 . 5 ) at the sprouting
apical bud (Time 1) f o r e i t h e r v a r i e t y .
Although magnesium provides one
O
O
CO
M
I"-
Q 6 / 6 uj
co
3.4.
u">
Fig.
Effect of
of cortex
0, 3, 6 and
tissue from
NITROGEN
9 lbs/acre MH on the nonprotein nitrogen content
Katahdin potato tubers grown on L. I. (Year 2 ) .
NON-PROTEI N
80
X
c
o
u
$
JC
o.
»w
0)
X
o
>■.
u
Effect of 0 and 3 lbs/acre MH on the protein content of cortex and pith t iss ues
from Katahdin potato tubers grown on L. I . , and Katahdin and Kennebec tubers grown
at Ithaca (Year 1 ) .
+
CO
N
(O
in
^
(1
•M 'Q J u a s j a j
CM
T-
O
3.5.
O
£
Fig.
PROTEIN
81
PROTEIN
82
x
o
O)
7V\ a
co
6 /6 LU
-J
<0^ o
OO
83
Ta bl e 3 . 1 .
The e f f e c t o f MH on th e macromineral c o m p o s i t i o n o f c o r t e x
and p i t h p o t a t o t i s s u e (MH a t 0 and 3 l b s / a c r e ) .
________________ Macromineral
K
L.
I.
P
(% P.M.)____________
Ca
Mg
Katahdin
Cx
+MH
Si g.
2.72 ± .09
2.90 + .08
P < 0.,01
.323 ± .003
.384 ± .002
P < 0.,01
.045 + .001
.053 + .000
P < 0. 01
.105 + .001
.107 + .000
N,.S.
Pi
+MH
Sig.
2.25 + .03
2.50 + .00
P < 0..01
.329 ± .001
.410 ± .002
P < 0.,01
.021 + .004
.029 + .001
N., s .
.101 + .001
.112 + .000
P < 0.,01
Cx
+MH
Sig.
2.23 + .06
2.08 + .03
N.,S.
.311 ± .005
.297 ± .006
N.,S.
.051
.001
.059 ± .003
P *C . 01
.010 + .001
.098 + .002
N.,S.
Pi
+MH
Sig.
2.26 + .03
1.97 + .01
P < 0. 01
.343 + .004
.303 + .001
P < 0. 01
.028 + .015
.027 + .003
N.,S.
.109 + .008
.095 + .001
P < 0. 01
Cx
+MH
Sig.
2.22 + .03
2.30 ± .01
N..S.
.299 ± .004
.323 ± .000
P < 0.01
.056
.001
.051 + .000
N. S.
.101 ± .001
.098 ± .000
N.S.
Pi
+MH
Sig.
1.97 ± .06
.01
1.94
0.
01
P <
.287 ± .006
.319 ± .001
P < 0.01
.022 + .001
.022 + .000
N. S.
.104 ± .004
.099 ± .001
N.S.
Ithaca Katahdin
Ithaca Kennebec
Data represents an average of 2 values ± S.D.
significant.
N.S.
represents not
84
Tab le 3 . 2 .
The e f f e c t o f MH on t h e m i c r o m i n e r a l c o m p o s i ti o n o f c o r t e x
and p i t h p o t a t o t i s s u e (MH a t 0 and 3 l b s / a c r e ) .
Micromineral
Mn
L .I.
Fe
Cu
(ppm D.W.)__________________
B
Zn
Katahdin
Cx
+MH
Sig.
17.2 ± 0 . 7
16.2 ± 0. 7
N.S.
8 7 . 4 ± 1.5
69.2 ± 0.7
P < 0.01
14.9 ± 0 . 6
15.8 ± 0. 2
N. S.
7.89 ± .19
7.96 ± .02
N. S.
32 .4 ± 0.2
28.1 ± 0.5
N..S.
Pi
+MH
Sig.
11.9 ± 1.0
12.0 ± 0.1
N.S.
20.9 ± 1.1
24.3 ± 1.4
P- '< 0.05
13.1 ± 0 . 6
14.1 ± 0 . 0
N.,S.
4.62 ± .26
4.87 ± .21
N. S.
3 0 . 4 ± 0.0
28.8 ± 0.4
N. S.
Ithaca Katahdin
Cx
+MH
Sig.
13.7 ± 0.1
14.1 ± 0 . 4
N.S.
53.5 ± 1.2
50.3 ± 2. 0
N,.S.
7 . 4 ± 0. 5
6. 6 ± 0. 2
N. S.
5.72 ± .16
5.59 ± .46
N. S.
25. 4 ± 0. 3
2 6 . 4 ± 2. 9
N. S.
Pi
+MH
Sig.
8.1 ± 1.4
9.3 ± 0 . 3
N.S.
25.7 ± 1.0
. 21.7 ± 1.1
P < 0.05
6. 6 ± 0. 6
5.7 ± 0. 5
N. S.
4.69 ± .60
3.43 ± .71
N. S.
27 .8 ± 0. 2
25.5 ± 1.5
N. S.
Ithaca Kennebec
Cx
+MH
Sig.
13.7 ± 1.1
9.7 ± 0. 5
p < 0.01
53.0 ± 3.3
55.0 ± 1.1
N,.S.
5. 5 ± 0. 6
5. 3 ± 0.1
N. S.
5.87 ± .03
5.54 ± .06
N. S.
23.1 ± 0.6
27.3 ± 0. 2
N. S.
Pi
+MH
Sig.
7.2 ± 0 . 5
7.2 ± 1.5
N.S.
19.9 ± 1.1
23.4 ± 2.1
P < 0.05
4.5 ± 0.2
5.1 ± 0.1
N. S.
4.30 ± .01
3.40 ± .66
N. S.
21.5 ± 1.8
24.5 ± 0.7
N. S.
Data represents an average of 2 values ± S.D.
significant.
N.S. represents not
85
Tab le 3 . 3 .
The e f f e c t o f MH on t h e macromineral and m ic r o m i n e r a l
c o m p o s i t i o n o f Ka tah din p o t a t o c o r t e x t i s s u e (MH a t 0 and 9
lb s /a c re ).
Macromineral
K
(% D.W.)
Ca
P
Mg
Cx
2. 14 ± .04
.277 ± .003
.045 ± .000
.087 ± .001
+MH
2. 28 ± .04
.356 ± .000
.039 ± .001
.086 ± .001
Sig.
N.S.
p < 0.01
p < 0.01
Micromineral
Cx
+MH
Sig.
N.S.
(ppm D.W.)
MN
Fe
Cu
13.0 ± 0 . 4
33.7 ± 0. 5
12.1 ± 0.1
5.80 ± .01
25.0 ± 0 . 2
9 . 6 ± 0. 2
33 .3 ± 1.1
15.4 ± 0.1
6.16 ± .01
28.8 ± 0.2
N.S.
N.S.
N.S.
P < 0.01
N.S.
Data represents an average of 2 values ± S.D.
s i g n i f i cant.
B
N.S.
Zn
represents not
86
Table 3 . 4 .
THe e f f e c t o f MH on th e macromineral c o m p o s i t i o n o f p o t a t o
t u b e r a p i c a l bud and s p r o u t t i s s u e (MH a t 0 and 3 l b s / a c r e ) .
Macromineral
D.W.)
P
Ca
Mg
3.45 ± .17
3.11 ± .11
N.S.
.410 ± .021
.409 ± .009
N.S.
.048 ± .001
.043 ± .001
N.S.
.131 ± .003
.108 ± .001
p < 0. 01
Bud
+MH
Sig.
3.58 ± .30
2. 28 ± .23
p < 0. 05
.478 ± .020
.445 ± .022
N.S.
.049 ± .007
.049 ± .001
p < 0.01
.146 ± .007
.122 ± .004
p < 0. 01
Sprouts
+MH
Sig.
2. 60 ± .04
2.47 ± .02
p < 0. 05
.664 ± .006
.694 ± .001
N.S.
.039 ± .001
.048 ± .001
p < 0.01
.189 ± .001
.197 ± .001
p < 0. 01
Time
Katahdin
0
Bud
+MH
Sig.
1
2
K
{%
Kennebec
0
Bud
+MH
Sig.
3.05 ± .17
3.23 ± .16
N.S.
.390 ± .028
.366 ± .025
N.S.
.037 ± .005
.037 ± .004
N.S.
.107 ± .005
.110 ± .009
N.S.
1
Bud
+MH
Sig.
3.43 ± .06
3.25 ± .05
N.S.
.385 ± .022
.399 ± .016
N.S.
.045 ± .003
.040 ± .003
N.S.
.109 ± .003
.109 ± .003
N.S.
2
Sprouts
+MH
Sig.
2.53 ± .01
2.29 ± .04
p < 0. 01
.654 ± .014
.732 ± .002
p < 0. 01
.042 ± .001
.068 ± .001
p < 0.01
.158 ± .002
.183 ± .001
p < 0. 01
Data represents an average of 2 values ± S.D.
significant.
N.S.
represents not
t is s u e
87
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3.5.
The effect of MH on the micromineral
(MH at 0 and 3 l b s / a c r e ) .
composition
of
potato
tuber
apical
CQ
•
r— r“ ~
a
•
CM v o
e
ro
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88
instance in which a s i g n i f i c a n t d i f f e r e n c e was found between the mineral
content of MH t r e a t e d and untreated api cal
t i s s u e s , the s i g n i f i c a n t l y
(p < 0 . 0 1 ) lower magnesium content found a t Time 1 (sp ro ut i n i t i a t i o n )
f o r the Katahdin v a r i e t y may simply r e f l e c t the lower content observed
in the unsprouted-MH t r e a t e d tubers (Time 0 ) .
In both v a r i e t i e s sprouts from potatoes rec e iv in g MH tre atment were
s i g n i f i c a n t l y (p < 0 . 0 1 ) higher in calcium, magnesium, manganese and
z i n c contents and lower in potassium content (Tables 3 . 4 and 3 . 5 ) .
In
the Kennebec v a r i e t y the phosphorus, i r o n , boron and copper contents of
sprouts from MH t r e a t e d tubers were s i g n i f i c a n t l y higher than sprouts
from untreated t ub er s.
The manganese content of sprouts was most
seve rely a f f e c t e d by maleic hydrazide.
Maleic hydrazide did not a f f e c t the accumulation o f minerals a t the
growing point nor the synthesis o f p r o t e i n in the t u b e r , however, MH
a f f e c t e d the balance o f es s en tia l minerals in the growing sprout t is s u e .
The g r e a t e r magnitude of e f f e c t observed f o r the Kennebec v a r i e t y
supports t h i s since MH was found to be a more potent i n h i b i t o r of
sprouting f o r the Kennebec v a r i e t y ( F i g .
3.7).
Since disturbances in
mineral balance may a l t e r enzyme a c t i v i t i e s and proper metabolic
functioning,
p r i o r mineral
i t may be t h a t the e f f e c t s i l l i c i t e d by MH are due to such
imbalances.
However, i t
is also known t h a t tr a c e elements
may be t o x i c to pl ants when present in more than usual t ra c e q u a n t i t i e s ,
thus the growth i n h i b i t i n g e f f e c t s of MH may be due to the excessive
accumulation of boron, copper, magnesium and/or zinc in the MH-treated
sprouts.
3.7.
o
z
u
Fig.
LU
Z
z
MH on the
UJ
of
LU
U
length
of
sprouts
from
the
Kennebec
and
<
Katahdin
Q
I
varieties.
2
o
h-
Effect
89
X
s
CQ
90
Fur th er studies using more so p hi s ti c a t e d techniques should be
undertaken in orde r to determine the e f f e c t o f MH on membrane
p e r m e a b il it y and on the subsequent movement and accumulation of ions in
germinating t i s s u e s .
M a t e r i a l s and Methods— CIPC
I - - T u b e r Tissue
Katahdin potatoes grown a t the Cornell Vegetable Research Farm a t
Riverhead, Long I s l a n d , were used in the study.
The tubers were
harvested 22 weeks fo ll o w in g p l a n t in g and were stored a t 5°C u n t i l
sampled one month l a t e r .
Twenty-four medium-sized tubers were randomly
selected and d i vi de d in to two groups.
One group was dipped f o r f i v e
minutes in a 1% CIPC aqueous emulsion and the o th er group was water
dipped.
A f t e r d i p p i n g , the tubers were allowed to a i r dry f o r 20
minutes and both were placed in separate k r a f t paper bags.
then stored a t 20°C u n t i l analyzed one month l a t e r .
These were
The tubers were
s l i c e d l o n g i t u d i n a l l y from bud to stem and then divided i n t o cortex
( in c lu d i n g the periderm) and p i t h sec tio ns.
Nitrogen and mineral
determinations were made according to the methods p r ev io us ly described
in the general experimental
procedures sec tion .
Analyses were made in
d u p li c a t e .
I I - - B u d Tissue
T h i r t y Katahdin potatoes were removed from storage a f t e r 6 months
and randomized by weight.
Ten potatoes were dipped in a
emulsion f o r f i v e minutes and the r e s t were water dipped.
1%
CIPC aqueous
A f t e r dipping
91
the tubers were dried and placed in K r a f t paper bags a t 5°C f o r f i v e
days.
Tubers were divided i n t o groups of ten as fo ll o w s :
Control Time 0 - -W a t e r dipped, analyzed immediately from
cold storage.
Control Time 1- - W a t e r dipped, stored a t 20°C f o r 1 week
( i n i t i a t i o n o f s p r o u ti n g ) .
CIPC Time 1--CIPC dipped, stored a t 20°C f o r 1 week.
Mineral analyses were made on bud t i s s u e , which consisted o f a 1 cm
long X 14 mm wide c y l i n d r i c a l
borer a t the api cal eye.
section cut w ith a a s t a i n l e s s steel
cork
The mineral content o f sprout t is s u e from
control and CIPC -trea ted tubers was not assessed because sprouting was
almost completely i n h i b i t e d by the CIPC trea tm en t.
Mineral
determinations were made according to the methods prev io us ly described
in the general experimental
procedures s e c tio n.
Analyses were made in
duplicate.
Results and Discussion
Nitrogenous Constituents
CIPC trea tme nt has no s i g n i f i c a n t e f f e c t on the t o t a l nitrogen
( F ig . 3 . 8 ) ,
(F ig .
non-protein nitrogen ( F i g . 3 . 9 ) or p r o t e i n content
3 . 1 0 ) o f cortex or p i t h tis s ue s o f Katahdin potatoes (Appendix
Table 2 . 3 ) .
As previously r e p o r t e d , maleic hydrazide treatment
s i g n i f i c a n t l y increased the c o r t i c a l
contents o f t o t a l
and non-protein
n i tr o g e n , however, the p r o t e i n content was only s l i g h t l y a f f e c t e d .
of
CIPC
U
X
on the
total
nitrogen
content
of
cortex
and
+
t is s u es .
I
pith
U
2
o
CN
in
o
M 'Q 6/6 uj
in
potato
o
Effect
u
3.8.
NITROGEN
c
Fig.
TOTAL
92
u
CL
Fig.
3.9.
Effect of CIPC
pith tiss ue s .
on the
nonprotein
content
of
potato
NITROGEN
nitrogen
NON-PROTEIN
cortex
and
93
PROTEIN
94
95
Mineral Content
CIPC trea tme nt had no s i g n i f i c a n t e f f e c t on e i t h e r the macromineral
(Table 3 . 6 ) or micromineral
(Table 3 . 7 ) content o f cortex or p i th
tissues of Katahdin potato t u b e r s , and also did not a f f e c t the
accumulation o f minerals a t the api cal bud (Tables 3. 6 and 3 . 7 ) .
Maleic
hydrazide had no e f f e c t on the mineral content o f tuber t i s s u e s ,
however, sprout t i s s u e was a f f e c t e d .
The mineral content o f sprout
t is s u e t r e a t e d w it h CIPC could not be assessed because sprouting was
sev er el y i n h i b i t e d by CIPC t re at m e nt .
Summary
Maleic hydrazide s i g n i f i c a n t l y (p < 0 . 0 1 )
increased the t o t a l
and
non -protein nitrog en contents o f cortex t is s u e o f Katahdin and Kennebec
potato tubers grown a t Long Isla nd or I t h a c a , but showed no a f f e c t on
pr o t e i n and mineral contents.
The sprout contents o f calcium,
magnesium, manganese and zinc o f Katahdin and Kennebec tubers grown at
Ithaca were s i g n i f i c a n t l y (p < 0 . 0 1 )
increased by MH t re at m e nt .
mineral content o f bud t is s ue was not a f f e c t e d .
however, did not a f f e c t the t o t a l
The
CIPC t re a tm e n t,
n i t r o g e n , non -protein n i tr o g e n ,
pr o t e i n or mineral content o f Katahdin tubers grown a t Long Isla nd .
Conclusion
Since d i f f e r e n c e s were found f o r t o t a l
and non-p ro te in nitrogen
content of cortex t i s s u e f o r the two i n h i b i t o r s , MH and CIPC e i t h e r do
96
Table 3 . 6 .
The e f f e c t of CIPC on the macromineral composition of
c o r t e x , p i t h and api cal bud t is s u e o f Katahdin potato
tuber s.
Macromineral
K
(% D.W.)
P
Ca
2.63 ± .00
2.68 ± .07
N.S.
.334 ± .000
.356 ± .008
N.S.
.043 ± .002
.038 ± .000
N.S.
100 ± .000
100 ± .001
N.S.
2.35 ± .06
2. 34 ± .03
N.S.
.325 ± .006
.343 ± .002
N.S.
.029 ± .013
.021 ± .000
N.S.
. 091 ± .003
093 ± .001
N.S.
2.91 ± .01
3.06 ± .04
3.05 ± .16
N.S.
.419 ± .012
.439 ± .014
.445 ± .008
N.S.
.097 ± .003
.051 ± .001
.059 ± .007
N.S.
. 114 ± .004
112 ± .006
110 ± .002
N.S.
Mg
Cortex
Control
+CIPC
Sig.
Pith
Control
+CIPC
Sig.
Apical Bud
Control Time 0
Control Time 1
+CIPC Time 1
Sig (Time 1)
Data represents an average o f 2 values ± S.D.
significant.
N.S represents not
of
97
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The effect of CIPC on the
Katahdin potato tub er s.
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not f u nc tio n in the same manner, or the two compounds stress tuber
tissue d i f f e r e n t l y .
Since n e i t h e r compound a f f e c t e d the p r ot ei n or
mineral content of potato t i s s u e , the use of e i t h e r i n h i b i t o r did not
reduce the n u t r i t i v e value o f the tu ber wit h regard to those p a r t i c u l a r
nutrients.
On the ot her hand, the use o f chemical
i n h i b i t o r s to
suppress sprouting o f stored potatoes is economically advantageous, and
is p a r t i c u l a r l y important in regions were the cl im a t e is warm and where
c o n t r o l l e d temperature storage is not a v a i l a b l e .
Thus, in t h i r d world
countries and underdeveloped nations where good storage conditions are
expensive and d i f f i c u l t to m ai n ta in , b e n e f i t s r e s u l t i n g from the use of
chemical
i n h i b i t o r s can be best r e a l i z e d .
Both MH and CIPC are r o u t i n e l y used in a g r i c u l t u r e , however, a
question e x i s t s as to whether maleic hydrazide is t o x i c to animals.
CIPC, on the o th er hand, has not been reported to be t o x i c , and i t s
presence in tu ber t i s s u e can be r e s t r i c t e d by simple washing.
agricultural
nutritional
the f i e l d ,
The
use o f CIPC f o r potatoes thus has economic b e n e f i t s without
or t o x i c o l o g i c a l
however.
implications.
CIPC cannot be applied in
Consequently, unless f i e l d a p p l i c a t i o n is re q u ir e d ,
the use o f CIPC should be advocated r a t h e r than MH.
COOKING STUDY
Intro d uc tio n
Potatoes are an important source of many n u t r i e n t s , y e t t h e i r
actual n u t r i t i o n a l
c o n t r i b u t i o n to the d i e t is dependent on a l t e r a t i o n s
and losses o f es se nt ial d i e t a r y components r e s u l t i n g from d i f f e r e n t
methods o f pre paration and cooking.
The cooking o f foods in
conventional ovens is a long es ta bl is he d p r a c t i c e , however, the use of
the microwave oven f o r both home and i n s t i t u t i o n a l meal prep a ra tio n has
r e c e n t l y increased due to i t s speed and convenience (Chung e t a l . ,
1981).
A recent survey o f 200 consumers who purchased fresh potatoes in
Texas supermarkets showed t h a t 16% owned microwave ovens, and t h a t a l l
owners who cook fresh potatoes in the microwave (56%) usually bake them
( B r i t t i n and Tr evi no, 1980).
However, the mechanism o f heat t r a n s f e r o f
microwave cooking d i f f e r s from t h a t o f conventional cooking methods and
may lead to di ff e r e n c e s in n u t r i e n t composition.
The primary d i f f e r e n c e between the supply o f heat v i a microwaves
and the more conventional ways is the i n i t i a l
d i s t r i b u t i o n of heat.
In
ordinary he a ti n g , energy is deposited on the surface of the ob j e c t and
conducted from there to deeper regions, whereas microwaves deposit heat
throughout a three-dimensional
surface burn (Rosen, 1972).
space and thus r e s u l t in less chance o f a
On the other hand, the generation of heat
throughout the e n t i r e product w i t h i n a r e l a t i v e l y short period o f time
during microwave cooking w i l l
cause the water w i t h i n c e l l s to be r a p i d l y
converted to steam, and the r a p i d l y expanding and escaping steam w i l l
cause the i n t e r i o r c e l l s to r up t ur e.
Mondy and M u e l le r (1977) found the
g r e a t e s t loss o f phospholipid in the cortex t i s s u e o f con ven tion ally
99
100
baked potatoes and in the p i t h of tubers baked by microwave, and suggest
t h a t during conventional baking the p i t h t is s u e is heated g r a d u a ll y
since i t
is p a r t i a l l y i n s u l a t e d by the c o r t e x , and thus less c e l l u l a r
d e s tr u c t i o n would occur in the p i t h of tubers baked in a conventional
oven.
Mondy and M u e l le r (1977) also found t h a t the crude l i p i d content
o f potatoes was s i g n i f i c a n t l y lowered by cooking and t h a t the loss was
highest in potatoes cooked in a microwave oven, l e a s t in bo i le d tu be rs ,
and in te rm ed ia te in tubers baked in a conventional oven.
find a sig nificant a lte ra tio n
They did not
in the f a t t y acid composition o f tubers.
The potato can provide a s i g n i f i c a n t c o n tr i b u t io n to the d i e t since
potatoes contain p r a c t i c a l l y a l l
es s e n t ia l d i e t a r y f a c t o r s w ith the
possible exception o f f a t and f a t - s o l u b l e indispensable n u t r i e n t s
(Woodward and T a l l y , 1953). The potato provides from 2-10% o f those
minerals except calcium f o r which U.S. recommended d i e t a r y allowances
have been est ab li sh ed ( i r o n , copper, i o d i n e , magnesium, phosphorus, and
zinc)
(True e t a l . ,
1978).
However, the mineral contents o f cortex and
p i t h t i s s u e may not be eq u iv a le n t since many of the microminerals tend
to accumulate more in the out er c o r t i c a l
region.
Diffe re n ce s in
n u t r i e n t content and r e t e n t i o n in the two tissues is important because
many consumers peel potatoes and also do not ea t the skin and the
adhering cortex t i s s u e of potatoes t h a t have been baked.
True e t a l . (1979) found t h a t cooking method had only a n e g l i g i b l e
e f f e c t on the mineral content of potatoes which were peeled fo ll o w in g
baking, y e t Augustin e t a l . (1979) observed t h a t n u t r i e n t r e t e n t i o n in
potato peel and f l e s h changed depending on the cooking method used.
101
Augustin e t a l . (1978) also i n v e s t i g a t e d the r e t e n t i o n of
w a t e r - s o l u b l e vitamins by several potato v a r i e t i e s using various home
prep ar at io n methods.
percent le v e l
Retention values in general exceeded the 85
f o r t h ia m i n , n i a c i n and vita min Bg, and the 70 percent
le v e l f o r ascorbic a c i d , r i b o f l a v i n and f o l i c ac i d .
In g e n e r a l, whole,
unpeeled, b oi le d and microwave baked potatoes e x h i b i t e d the highest
vitamin r e t e n t i o n , although i n d i v i d u a l
v a r i e t i e s demonstrated d i f f e r e n t
retentions.
When vegetables are prepared in w a te r, the cooking time and amount
of water used are the determining f a c t o r s in r e t e n t i o n o f n u t r i e n t s
(Thomas e t a l . ,
1949) and l i t t l e
info rmation is known concerning changes
in n u t r i e n t s r e s u l t i n g from microwave cooking o f vegetables withou t
added wa te r.
Thomas e t a l . (1949) found g r e a t e r losses o f w a te r - s o l u b l e
n u t r i e n t s due to leaching when vegetables were b o i le d or microwave
cooked in water as compared to pressure cooking, and a t t r i b u t e d the
g r e a t e r losses to the l a r g e r q u a n t i t i e s of water used during b o i l i n g and
microwaving.
Decreased cooking time employed during high frequency
cooking also showed a tendency toward increased n u t r i e n t r e t e n t i o n in
the vegetables, however, the e f f e c t o f the decreased cooking time was
not as marked on the r e t e n t i o n of n u t r i e n t s as the e f f e c t of amount of
cooking water.
Mabesa and Baldwin (1979) compared peas cooked with and without
water in a microwave oven.
Cooking peas without added water re su lt ed in
lower moisture content than raw peas and those cooked by o th er methods,
however, peas cooked by microwave tended to be s i g n i f i c a n t l y higher in
ascorbic acid content than peas cooked co n v e n t io n a ll y .
Peas with added
102
water cooked by microwave contained s i g n i f i c a n t l y less ascorbic acid
than those cooked w ith ou t w a t e r , and peas cooked c o n v en t io na lly
contained s i g n i f i c a n t l y less ascorbic acid than peas cooked by microwave
wit ho ut wa ter.
Chung e t a l . (1981) also used peas to compare the e f f e c t o f
microwave and conventional cooking on n u t r i t i v e va l u e .
cooking produced a s l i g h t l y higher loss of f a t ,
Conventional
however microwave
cooking produced a higher p r o t e i n loss than conventional cooking.
Although the p ro te in content o f the potato is only about 2% on a wet
weight b a s i s , the n u t r i t i v e value is very hig h, thus a l t e r a t i o n s in
pr o t e i n q u a n t i t y and q u a l i t y are n u t r i t i o n a l l y important.
This study was undertaken in order to i n v e s t i g a t e the changes in
nitrogenous c on st it ue nt s and mineral content o f potatoes f o l l o w in g
microwave and conventional baking.
Potatoes provide a model f o r
microwave cooking of vegetables without water and a s i g n i f i c a n t
nutritional
c o n t r i b u t i o n to the d i e t .
M a t e r i a l s and Methods
Katahdin potatoes grown a t the Cornell
Vegetable Research Farm a t
Riverhead, Long Island were used in the study.
5°C u n t i l
analyzed.
Tubers were stored a t
F i f t e e n potatoes of medium s iz e were baked
according to one of the f o l l o w in g methods:
1. Co nventi onal--Potatoes were placed in a 400°F oven f o r 60
minutes.
103
2. Microwave--Each potato was cooked se p ar at el y by pla cin g i t
in to a L i t t o n microwave (2450 MHz) f o r a t o t a l
o f 3 minutes
(1 1/2 minutes on each s i d e ) .
All
potatoes were allowed to cool but were s t i l l warm when each was
separated in to cortex ( in c l u d i n g the periderm) and p i th sec tio ns.
Sections were then f r o z e n , l y o p h i l i z e d in a Stokes f r e e z e - d r y e r , ground
in a Wiley m i l l
through a 40 mesh screen and stored under nitrog en u n t i l
analyzed f o r nitrogenous co n sti tu ent s and m in er als .
Analyses were made
according to procedures prev io us ly described in the general experimental
procedures sec tion .
Results and Discussion
Total Nitrogen
Conventional baking of potatoes s i g n i f i c a n t l y (p < 0 . 0 5 )
the t o t a l
nitrogen content o f cortex t is s u e and s i g n i f i c a n t l y
increased pi th t o t a l
(p < 0 .0 1)
nitrog en ( F i g . 4 . 1 , Appendix Table 3 . 1 ) .
baking did not a f f e c t the t o t a l
pith tota l
reduced
Microwave
nitrogen content of cortex t i s s u e , y e t
nitrogen was s i g n i f i c a n t l y
(p < 0 . 0 1 ) reduced ( F i g . 4 . 1 ,
Appendix Table 3 . 1 ) .
Non-Protein Nitrogen
The non-protein nitrogen content o f potato cortex t is s u e was not
a l t e r e d f o ll ow in g conventional
Table 3 . 1 ) .
(p < 0 . 0 1 )
or microwave baking ( F ig . 4 . 2 , Appendix
Conventional cooking, however, r es u lt ed in a s i g n i f i c a n t
increase in p i t h non-protein nitrogen con tent, wh ile
pith
potato
tissue.
Cont.
TOTAL
= control,
micro.
= microwave.
NITROGEN
104
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microwave cooking s i g n i f i c a n t l y
(p < 0 . 0 1 ) reduced the non-protein
nitrogen content of p i t h t is s u e ( F i g . 4 . 2 , Appendix Table 3 . 1 ) .
Prot ei n and Amino Acids
The p r o t e i n content o f both tissues were reduced as a r e s u l t of
both baking methods ( F i g . 4 . 3 , Appendix Table 3 . 1 ) .
baking also caused reductions in t o t a l
Conventional
and f r e e amino acid contents in
the cortex by about 3% and 15% r e s p e c t i v e l y , y e t caused the t o t a l
and
f r e e amino acid contents o f the p i th to increase by 9% and 8%.
Microwave baking, however, caused increases o f 2% and 8% in the c o r t e x ,
and decreases o f 4% and 17% in the p i t h .
Individual
amino acids
demonstrated d i f f e r e n t trends as a r e s u l t o f both cooking methods
(Tables 4.1 and 4 . 2 ) .
The reduction in t o t a l
n i tr o g e n , p r o t e i n and amino acid contents
o f cortex t is s u e concomitant with an increase in t o t a l
nitrogen,
non -protein nitrogen and amino acid contents o f p i t h t is s u e f o ll o w in g
conventional
baking is c o n si s te n t with the r e s u l t s observed by Mondy
and M u e l le r (1979) f o r phospholipid content.
High and prolonged heat
in the cortex area could r e s u l t in both g r e a t e r membrane damage and the
degradation o f some p r o t e i n i n t o f r e e amino aci ds.
In a d d i t i o n , the
long baking process allows time f o r the leaching of nitrogenous
c o n s t i t u e n t s , p a r t i c u l a r l y f r e e amino a c i d s , i n t o the p i th t i s s u e from
the c o r t e x .
The decrease in t o t a l
nitrogen in the c o r t e x , and i t s
increase in the p i th may thus be due to mig ration o f
nitrogenous
compounds from one p a r t of the tuber i n to the o th er during conventional
oven-baking.
According to Fig. 4 . 1 , a discrepancy appears in the data
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since there is a decrease in t o t a l
nitrog en of about 4% in the cortex
y e t an increase o f some 11% in the p i t h .
However, since percentage
changes f o r each t is s u e are being compared with values obtained from
another group of tubers ( un tre at e d c o n t r o l s ) , the inconsistency in the
q u a n t i t a t i v e changes may be a r e s u l t o f v a r i a t i o n between tubers w it h in
a group.
The la r g e reduction iri glutamine content in both cortex and
p i t h suggests amino acid de s tr u c t io n as a r e s u l t of conventional baking.
The reduction in the contents o f a l l
nitrogenous co n s ti t u e n t s in
the p i t h t is s u e o f microwave baked potatoes is also c on si s te n t with the
f in d in g s o f Mondy and M u e l le r ( 1 9 7 7 ) .
During microwave cooking, the
generation of heat throughout the e n t i r e tuber w i t h i n a r e l a t i v e l y short
period of time causes the water w i t h i n c e l l s to be r a p i d l y converted to
steam, and the r a p i d l y expanding and escaping steam ruptures the c e l l s .
There is thus the oppo rtu ni ty f o r loss o f v o l a t i l e components which are
generated during cooking.
Deck e t a l . (1973) i d e n t i f i e d e i g h t nitrogen
compounds as a components of the f l a v o r generated during the cooking of
potato chips.
The reduction in glutamine content p r i m a r i l y in the p i t h
t is s u e fo ll o w in g microwave baking also suggests t h a t microwave
processing is capable o f destroying t h a t amino aci d.
The reduction in
pr o t e i n and the increase in amino acid content in the cortex tissue
ind ic at es t h a t some amino acids may have been released from pr ot ei n in
the c o r t e x , y e t the short heating period did not al low time f o r leaching
i n t o the i n t e r i o r p i t h t is s u e .
m
Mineral Contents
Conventional baking s i g n i f i c a n t l y (p < 0 . 0 1 ) reduced the potassium
content o f cortex t is s u e and s i g n i f i c a n t l y (p < 0 . 0 5 )
potassium content o f the p i t h (Table 4 . 3 ) .
abundant mineral
in the pota to.
increased the
Potassium is the most
Such a compositional change suggests
t h a t potassium leached from cort ex to p i t h t i s s u e , and is in agreement
with compositional changes observed f o r nitrogenous co n sti tu ent s and
i r o n , the micromineral present in the g r e a t e s t q u a n t i t y .
Conventional
baking r e s u l t e d in a s i g n i f i c a n t (p < 0 . 0 5 ) reduction in c o r t i c a l
con tent, and a s i g n i f i c a n t (p < 0 . 0 5 )
p i th t is s u e (Table 4 . 4 ) .
iron
increase in the iron content o f
L e v i t t and Todd (1952) found t h a t iron is
complexed with the pr ot ei n in potatoes more abundantly than any ot her
t r a c e m in e r a l.
Perhaps iro n was released during p r o t e i n degradation.
The copper content o f p i t h t i s s u e was s i g n i f i c a n t l y (p < 0 . 0 5 ) reduced
fo ll o w in g conventional baking, however, no s i g n i f i c a n t e f f e c t s were
observed in e i t h e r t iss ue f o r phosphorus, calcium, magnesium,
manganese, boron or zinc (Table 4 . 4 ) .
Microwave baking s i g n i f i c a n t l y (p < 0 . 0 5 )
increased the potassium
and calcium contents (Table 4 . 3 ) and s i g n i f i c a n t l y
the copper content of p i t h t i s s u e (Table 4 . 4 ) .
(p < 0 .0 5)
reduced
These changes cannot be
explained a t the present ti m e , but they i n d ic a t e a need f o r ad d it io n al
work and the use o f more s o p h is ti c a t e d techniques in order to more
thoroughly t ra c e the movement of mineral components during each o f the
processing treatments.
112
Table 4 . 3 .
Infl uen ce o f baking method on the macromineral
(% D.W.) o f poatoes.
content
Cortex
Raw
Macromineral
Potassium
2. 69
± .16
Conventional
2. 29
± .11
Microwave
2.72
± .04
Phosphorus
.384 ± .023
.338 ± .017
.375 ± .007
Calcium
.051 ± .001
.050 ± .005
.052 ± .002
Magnesium
.114 ± .005
.103 ± .004
.118 ± .003
P it h
Raw
Macromineral
Potassium
2. 48
± .06
Conventional
3. 03
± .26
Mi crowave
2.81
± .03
Phosphorus
.383 ± .013
.423 ± .001
.384 ± .018
Calcium
.023 ± .001
.024 ± .000
.027 ± .001
Magnesium
.103 ± .003
.107 ± .001
.102 ± .004
Data are reported as an average of two values ± S.D.
113
Table 4 . 4 .
In fl u e n c e o f baking method on the micromineral content (ppm)
o f potatoes.
Cortex
Micromineral
Conventional
Raw
11.40 ±
.85
11.70 ±
Manganese
12.85 ±
Iron
88. 10 ± 1.56
77.80 ± 2.69
85.95 ± 1.20
Copper
13.55 ±
.64
12.55 ±
13.05
9. 23 ±
.77
8.05 ± 1.03
9.22 +
.45
21.95 ±
.92
19.95 ± 1.06
21.85 ±
.35
.19
9.84 ±
.51
29. 70 ± 2.40
21.80 ±
.28
Boron
Zinc
.50
Mi crowave
.50
±
.40
.21
Pith
Manganese
9.43 ±
9. 05 ±
.62
Iron
24.25 ±
.07
Copper
10.75 ±
.35
9.95 ±
.07
9.65 +
.21
6.24 ±
.25
6. 70 ±
.16
6.54
±
.34
21.65 ±
.35
29.55 ± 4.17
21.70
±
1.27
Boron
Zinc
Data are r e p o r t e d as an average o f two v a lu e s ± S.D.
114
Summary
Conventional baking reduced the c o r t i c a l contents o f t o t a l
nitrogen by 4%, t o t a l amino acids by 3%, f r e e amino acids by 15%, and
potassium and i ro n by 15% and 12%.
Conventional baking increased the
p i t h contents o f t o t a l nitrog en by 11%, non -protein nitrogen by 20%,
total
amino acids by 9%, f r e e amino acids by 8%, and potassium and iron
by 22% and 23%.
total
Microwave baking increased the c o r t i c a l
contents o f
amino acids by 2% and f r e e amino acids by 8%, y e t reduced the
p i t h contents o f t o t a l nitrog en by 16%, non -protein nitrogen by 18%,
total
amino acids by 4%, and f r e e amino acids by 17%.
had only s l i g h t e f f e c t s on mineral composition.
Microwave baking
I n d iv id u a l amino acids
demonstrated d i f f e r e n t trends as a r e s u l t of both cooking methods.
Conclusion
Results suggest t h a t d i f f e r e n t baking methods may lead to
compositional changes in nitrogenous co n sti tu en ts and minerals of
potatoes, depending on the mechanism o f heat t r a n s f e r and the
p a r t i c u l a r t i s s u e under i n v e s t i g a t i o n .
Conventional
heating p r i m a r i l y
re su lt ed in the migration o f some n u t r i e n t s from cortex to p i t h ,
whereas microwave baking r e s u l t e d mainly in the loss o f v o l a t i l e s from
the i n t e r i o r p i t h t is s u e .
When baking potatoes, i t appears t h a t conventional
heating is
superior to microwave cooking with respect to nitrog en and mineral
contents, e s p e c i a l l y when the skin and adhering c o r t i c a l
consumed.
tiss ue are not
115
These recommendations, however, p e r t a i n only to the conditions of
the study.
Since potatoes were baked i n d i v i d u a l l y in the microwave
oven, t o t a l
cooking time was only 3 minutes.
I f a g r e a t e r number of
potatoes had been baked t o g e t h e r , cooking times would have been much
lon ger .
Since cooking time can have a l a r g e a f f e c t on mig ra tio n and
loss o f n u t r i e n t s , the e f f e c t s r e s u l t i n g from microwave baking of
individual
potatoes found in t h i s study might not r e f l e c t changes t h a t
would have occurred over longer periods o f cooking.
Furt her studies
should be conducted in order to determine compositional changes
r e s u l t i n g from d i f f e r e n t periods o f microwave baking.
POTATO/WHEAT SNACK
In tr o d u c t io n
The word "snack" comes from the Middle Dutch verb "snacken"
meaning to snap up.
I t is u s u a ll y app lied to products which are eaten
as a quick meal or served as a meal complement (Sacharow, 1969).
Chipper/Snacker magazine ( M o r r i s , 1981a) reported t h a t the 1980 sales
volume f o r the s a l t e d snack ind us tr y exceeded 4 . 5 b i l l i o n d o l l a r s ,
representing a 19% increase over l a s t years t o t a l
Potato chips s t i l l
ind us tr y sales.
reign supreme in the world of snacks with
manufacturers' sales o f $1.9 b i l l i o n , however, corn products are
growing r a p i d l y and c o r n / t o r t i l l a chips topped $1 b i l l i o n f o r the f i r s t
time in h i s t o r y .
The 1980 snack food sales volume was as fo llo w s:
Potato chips $1 .9 b i l l i o n , corn chips $390 m i l l i o n , r e g u l a r t o r t i l l a
chips $470 m i l l i o n ,
round t o r t i l l a chips $150 m i l l i o n , popped corn $100
m i l l i o n , nuts $900 m i l l i o n , extruded snacks $220 m i l l i o n , sal te d meat
snacks $220 m i l l i o n and p r e t z e l s $210 m i l l i o n .
In 1981 the ind us tr y g i a n t F r i t o - L a y embarked on a nationwide
marketing campaign to increase snack s al es .
impressive:
The F r i t o - L a y message was
1) Salted snacks are more than 10 times as p r o f i t a b l e as
the average supermarket item because of t h e i r higher than average
margins and lower than average s e l l i n g expenses; 2) The average snack
category p r o f i t a b i l i t y accounts f o r about 14 percent o f the stores net
p r o f i t s from 1.22 percent o f t o t a l
sa le s; 3) The average gross margin
f o r salte d snacks is 27 per cent, compared to 22 percent f o r the average
supermarket item; 4) More than 50 percent of the average item' s gross
116
117
margin is consumed by handling cos ts, wh ile f o r s a l t e d snacks the
f i g u r e is less than 30 percent; 5) The snack category grew 16.9 percent
in 1980; 6) Between 1975-1980, t o t a l
snack sales increased an average
68 percent; and 7) Snacks rank 18th in t o t a l
st or e s a l e s , 17th in gross
p r o f i t margin, 15th in gross p r o f i t c o n t r i b u t i o n and 1st in r e t u r n on
investment ( M o r r i s , 1981b).
One o f the major problems confronted by snack food manufacturers
in 1980, however, was g e t t i n g adequate supply o f potatoes and high
prices paid f o r the commodity.
In a d d i t i o n , i t
continuing high potato prices w i l l
r e s u l t in continuing high consumer
prices f o r potato chips ( M o r r i s , 1981b).
m a t e r ia l
costs f o r a l l
is a n t i c i p a t e d t h a t
Since almost 27 percent of
snack foods can be a t t r i b u t e d to potatoes (43.4%
f o r potato c h i p s ) , y e t only 0.1% o f ma te ria l costs go to inexpensive
and less peri sh ab le f l o u r s
(0.0% f o r potato c h i p s ) , a reasonable
a l t e r n a t i v e to potato chips might be a potato/wheat extruded snack
product.
Growth in d o l l a r sales f o r the combined category o f extruded
snacks, popped popcorn and meat snacks f o r 1980 was a healthy 18.9
p er ce nt , however, the outlook is not so o p t i m i s t i c f o r 1981.
Manufacturers expect a modest d o l l a r volume growth o f only 8 . 4 percent,
thus a new d e s ir a b l e product could prove a su b s ta n ti a l boost to t h a t
d e c li n in g market.
The p r i n c i p l e of ext rus io n has been applied from the p l a s t i c
indust ry and the extru der is now one of the most v e r s a t i l e machines f o r
developing new snack and f a b r i c a t e d foods.
The basic functions o f the
cooking e x t r u d e r are moisture entrainment, g e l a t i n i z a t i o n of st arches,
pr ot ei n d e n a t u r a t i o n , heat l a b i l e growth i n h i b i t o r control and
r e s t r u c t u r i n g and r e t e x t u r i n g o f process mat eria l
(Smith, 1974).
These
118
changes are achieved by feeding p ro te in m ix tu r es , p r i n c i p a l l y vegetable
f l o u r s , water and supplementary a d d it iv e s i n t o the cooking b a r r e l
r a i s i n g the temperature and pressure.
and
The r e s u l t i n g p l a s t i c mass is
extruded through a di e to the atmospheric pressure causing re le a s e of
steam and expansion o f the m a t e r i a l .
A f t e r co o li n g , the product sets
i n t o a s t r u c t u r e with completely d i f f e r e n t c h a r a c t e r i s t i c s than those
o f the s t a r t i n g m a t e r ia l
( I y e r , 1978).
Snack foods in g e n e r a l , are based on starch and have l i t t l e
on p r o t e i n n u t r i t i o n .
effect
However, potato and wheat f l o u r possess
complementary p r o t e i n , and when combined can produce a product with
higher q u a l i t y p r o t e i n than e i t h e r i n g r e d i e n t could provide on an
individual
basis.
This study was t h e r e f o r e undertaken in orde r to
formulate and produce a new extruded potato/wheat snack o f enhanced
n u t r i t i v e value.
M a t e r i a l s and Methods
In gr ed ie nt s
1.
Drumdried potato f la k e s (Grand Union brand) were purchased
from the r e t a i l
2.
market and used as needed.
F l o u r s - - P i l l s b u r y brand p r e - s i f t e d , a l l
purpose enriched
white f l o u r and whole wheat (graham) f l o u r were purchased
from the market and used as needed.
3.
S t e r l i n g brand iod ize d t a b l e s a l t was purchased from the
market and used as needed.
4.
The in te rm ed ia te product (extruded) was f r i e d in Crisco brand
p a r t i a l l y hydrogenated soybean o i l
purchased at r e t a i l .
119
Product Formulations
1.
1 : 1 - - P o t a t o : W h i t e F l o u r , s a l t 1.5%.
2.
2 : 1 — PotatorWhite F l o u r , s a l t 1.5%.
3.
2 : 1 - - P o t a t o : F l o u r ( 1 / 2 w h i t e , 1 / 2 whole w he at ), s a l t 1.5%.
Process Conditions
T r i a l s were performed in a 5 head Wenger X-5 l a b o r a t o r y e xt ru de r
(Wenger Mfg; Sabetha, Kansas) Fig. 5 . 1 , by using a 1/8"
(3 .1 7 5 mm) d i e .
D e t a i l s of the ex t r u d e r are as f o llo w s:
Screw speed
500-600 rpm
Feed r a t e
8-10
Water r a t e
0.5 g/hr
Steam pressure
75-80 psi
A i r pressure
125 psi
Ampere o f motor
11.3 amps
Motor-chopper
25-30 rpm
Moisture Content
Moisture content was determined by drying samples in a vacuum oven
a t 68°C and 30 psi f o r 24 hours.
Oil Content
Oil content was determined by g ri nd in g approximately 15 g of
sample in a mortar and p es tl e followed by e x t r a c t i o n with
chloroform/methanol as described e a r l i e r f o r crude l i p i d .
Fig.
LU U1
I ’ 11111*1•I *
5.1.
Extruder
heads
and
screw.
120
lij
121
Te x tu r a l Determinations
The In st ro n Universal Testin g machine was used to determine
textural
p r o p e rt ie s o f the f r i e d product.
was placed on a steel
(fir s t b ite ).
o f product.
A 1/ 2 inch piece of product
support and compressed by a f l a t st eel
plate
A second b i t e determination was made on the same piece
Four pieces o f product were used f o r each t re at m e nt .
The
c h a rt speed, cross head speed, and time f o r r e l a x a t i o n between b i t e s
was kept constant.
The f o l l o w i n g sample o f a t y p i c a l fo rc e- de fo rm a tio n
curve i n d ic a t e s the points a t which the values f o r b r i t t l e n e s s ,
hardness, compression, springiness and cohesiveness can be determined:
hardness
= cohesiveness
brittleness
-------- V—------- .J
compression
springiness
b r i t t l e n e s s - - f o r c e with which a sample ruptures or f r a c t u r e s ,
hardness— force necessary to a t t a i n a given deformation or
compression.
s p r in gi ne ss — degree to which a sample returns to i t s o r i g i n a l
shape once i t has been deformed or compressed,
cohesiveness— e xt en t to which a sample can be deformed before i t
ruptures.
122
Sensory Evaluation
Two t a s t e panels were conducted:
Cornell
1) a 24 member panel composed of
students, f a c u l t y and employees was asked to ev al ua te the
appearance, t e x t u r e and f l a v o r of the th re e product for mu lation s using
a 7 - p o i n t hedonic scale (7 = l i k e e xt r em el y, 1 = d i s l i k e e x t r e m e l y ) ,
and to rank the t hr ee products in order o f preference; 2) twelve
members of the f i r s t panel who d i s l i k e d the t e x t u r e of the f r i e d
product were asked to ev al ua te the d r i e d product in the same manner as
be fo re.
The score sheet used to ev al ua te product is shown in Fig. 5 . 2 .
S t a t i s t i c a l Analysis
Sensory data was analyzed by ANOVA and LSD t e s t , or by Friedman's
Rank t e s t and Friedman's S i g n i f i c a n t D i f f e r e n c e .
Results and Discussion
Stan da rdi za tio n o f Formulas
This was done by s e l e c t i n g the best l e v e l s of i n g r ed ie nt s so as to
y i e l d a high q u a l i t y product in terms o f ease of extrusion and
org an ol e pt ic q u a l i t i e s .
The f i r s t fo rm u lat io n consisted of a 1 to 1
mixture of potato to white f l o u r .
Since the product which came out of
the ex t r u d e r ( i n t e r m e d i a t e ) had a chewy consistency both before and
a f t e r f r y i n g , a second for mul at io n con si s tin g of a 2 to 1 mixture of
potato to white f l o u r was t r i e d .
This too had a chewy consistency.
Since i t was thought t h a t the chewiness was due to the high gluten
content of the f l o u r , a mixture o f wh ite and whole wheat f l o u r was
123
POTATO/WHEAT SNACK TASTE PANEL
Name______________________________
You have been given three d i f f e r e n t formulations o f a potato/wheat
snack.
Please r a t e them according to t h e i r appearance, t e x t u r e and
f l a v o r by checking one response f o r each for mu lat io n under each
category.
Evaluate them in the f o l l o w i n g order A
o
.
Appearance
ye_
Flavor
Texture
_a _ _o_ j#
A
o
7. Like Extremely
___
___
___
___
___
__
6. Like Moderately
___
___
___
___
___
__
5.
Like S l i g h t l y
___
___
___
___
___
__
4.
N e it h e r Like
nor D i s l i k e
___
___
___
___
___
__
Dislike S lig h tly
___
___
___
___
___
__
2. D i s l i k e Moderately
___
___
___
___
___
__
1. D i s l i k e Extremely
___
___
___
___
___
__
3.
A
O
*
Please i n d i c a t e the order of your preference f o r these products.
1.
2.
3.
Fi g. 5 . 2 .
Taste Panel Score Sheet.
The order of pr ese nta tio n was
changed f o r each product so t h a t an e q u iv a le n t number of each
pr ese nta tio n order was presented, and order o f pr ese ntation
bias was el im i n a t e d .
124
t r i e d in the hope t h a t the presence o f bran in the whole wheat would
cut the gluten and reduce the chewiness.
The f i n a l
formulations were
ordered as f ol lo w s:
1.
1 : l - - P o t a t o : W h i t e F l o u r , s a l t 1.5%.
2.
2 :l--P o ta to :F lo u r (1/2 white,
3.
2 : 1 — Potato:White F l o u r , s a l t 1.5%.
1/ 2 whole w h e a t ), s a l t 1.5%.
Extrusion
Before an acceptable extruded product could be produced, i t was
necessary to extrude a s u b s ta n ti a l
q u a n t i t y of each mixture w hi le
simultaneously ad ju s t in g the hopper feed r a t e , wa te r flow r a t e and
heat.
I f the steam (h eat)
in the f i n a l
heads was not gr adu all y
increased to cooking temperatures, the product cooked too f a s t and
clogged the d i e .
In a d d i t i o n , the flow r a t e o f water as i t mixed wit h
the product was c r u c i a l
in both preventing the d i e from clogging and
a t t a i n i n g an acceptable extruded t e x t u r e .
Too l i t t l e
water caused
overcooking and clogging, y e t too much water prevented cooking and
puffing.
The f i n a l
processing conditions are reported in M a t e r i a l s and
Methods.
The product issuing from the e xt ru de r was in the form o f a
s l i g h t l y p u f f e d , continuous c y l i n d r i c a l
s t r i p , which was l a t e r cut i n to
pieces approximately 1 . 5 - 2 inches in length ( F i g .
5.3).
Frying
The extruded ( in t e r m e d i a t e ) product was considerably chewy and
very pale in c o l o r ( F ig . 5 . 3 ) ,
o il.
so i t was deep f a t f r i e d
in vegetable
The f r y i n g co n d it io n s , and moisture and f a t content o f the
125
H <
c$vri
Fig.
5.3.
Extruded product.
Fig.
5 .4 .
Fried product, 1 = 1:1 ( w h i t e ) , 2 = 2:1
wheat), 3 = 2 : 1 (w h ite ).
( 1 / 2 whole
126
r e s u l t i n g f r i e d product, as well as the moisture content of the i n t e r ­
mediate product are given in Table 5 . 1 .
I t was observed t h a t the
product w it h the lowest i nt e rm ed ia t e moisture content ( 2 : 1 , 1/ 2 whole
wheat) also had the lowest moisture content o f the f r i e d product y e t
absorbed more o i l .
The o i l
content o f the t h r ee products ranged from
13-18%, which compared q u i t e f av or ab ly w ith a 40% o i l
content f o r
potato chips.
During f r y i n g the i nt er m ed iat e product tends to p u f f more and
develop a golden c o l o r ( F i g . 5 . 4 ) .
The in te rm ed ia te product contains
s a l t and moisture which are believed to have an e f f e c t on i t s f r y i n g
c h a r a c t e r i s t i c s and the o i l
absorption.
A c e r t a i n po rt io n o f the s a l t
c r y s t a l l i z e s on the o u t e r surface o f the product and t h i s
c r y s t a l l i z a t i o n is g r e a t l y increased when i t
is immersed in hot o i l ,
which may give r i s e to b o i l i n g nuclei and aid moisture t r a n s f e r out of
the product.
At the same ti m e , moisture imprisoned in the i n t e r i o r is
r a p i d l y heated and driven o u t , c r e a ti n g expansion of the starchy
m a t e r ia l and aiding in the prevention o f f a t p e n et ra ti on i n t o the
i nterior.
Sensory Evaluation
The sensory assessment o f the t h r ee formulations of the f r i e d
product i s in dicated in Table 5 . 2 .
found f o r appearance or f l a v o r .
No s t a t i s t i c a l
However, a l l
d i f f e r e n c e s were
mean values f o r those
c h a r a c t e r i s t i c s were above 5 , which in d ic a t e s t h a t both appearance and
f l a v o r were ge n e r a ll y l i k e d by the p a n e l i s t s .
Histograms of the
number of responses f o r each score are shown in Figs. 5 . 5 and 5 . 7 .
all
For
three product for mu latio ns the m a j o r i t y o f responses f o r appearance
127
Table 5 . 1 .
The moisture content of the i nt e rm ed ia t e product, and the
moisture and f a t contents o f the f r i e d product cooked at
190-195°C.
Product
Moisture
(%)
Fat
(%)
Interm ed iat e
1:1
(white)
15.5
13.3
14.4
2:1
( 1 / 2 whole wheat)
12.6
11.7
12.2
2:1
(white)
15.4
14.7
15.1
Fried
1:1
(15
(w h i t e )
sec cook)
2:1 ( 1 / 2 whole wheat
(9 sec cook)
2:1
(18
(w h i t e )
sec cook)
7.8
9.2
8.5
14.2
15.7
TO '
6.8
7.1
17.7
18.3
O
TF70
8.8
9.8
9 .3
12.7
13.2
T O
128
Table 5 . 2 .
Sensory e v a lu a tio n of appearance, t e x t u r e , f l a v o r and
preference of three fo rmulations of the f r i e d product
(N = 24)
Mean
Product
Appearance
Texture
Flavor
Sig.
1:1
2:1
2:1
( w hi te )
( 1 / 2 whole wheat)
( w hi te )
5.50
5.33
5.96
2.18
N.S.
1:1
2:1
2:1
( w hi te )
( 1 / 2 whole wheat)
(wh it e)
3.38
4.71
3.25
12.89
1 ab
2 b
3 a
1:1
2:1
2:1
(w h i t e )
( 1 / 2 whole wheat)
(w h i t e )
5.30
5.38
5.25
0.09
N.S.
Mean
X2
Sig.
1.92
2.29
1.79
3.25
N.S.
Product
Preference
F
1:1 ( w hi te )
2:1 ( 1 / 2 whole wheat)
2:1 ( w hi te )
N.S. represents not s i g n i f i c a n t .
l e v e l (p < 0 . 0 5 ) .
Statis tical
d i f f e r e n c e is at the 95%
129
TRERT. I
J
TRERT. 2
TRERT. 3
I
2
3
M
E
E
7
SCORES
Fig.
5.5.
Appearance of the f r i e d product.
T r e a t . 1 = 1:1
( w h i t e ) , T r e a t . 2 = 2:1 ( 1 / 2 whole wheat),
T r e a t . 3 = 2:1 ( w h i t e ) .
Arrows point to treatment
means.
130
TRERT.
I
TRERT. 2
1
J
TRERT. J3-
J
H
S
SCORES
Fig.
5.6.
Texture o f the f r i e d product.
Treat. 1 = 1 : 1 (w hite),
T r e a t . 2 = 2:1 ( 1 / 2 whole wh eat ), T r e a t . 3 = 2:1
(white).
Arrows point to tre atment means.
131
TRERT. I
TRERT. 2
T
TRERT. 3
f
CIZ I
I
2
3
M
S
G
7
5<URE5
Fig.
5.7.
Flavor o f the f r i e d product.
Treat. 1 = 1 : 1 (white),
T r e a t . 2 = 2:1 ( 1 /2 whole whea t), T r e a t 3 = 2: 1
(white).
Arrows point to treatment means.
132
and f l a v o r l i e a t the " l i k e " end ( r i g h t side) o f the sc a le .
fo r texture (Fig.
5.6),
Responses
however, l i e a t both ends o f the sc a le , which
suggests a dichotomous panel composed o f people t h a t l i k e chewiness and
those t h a t d i s l i k e chewiness.
The mean scores f o r t e x t u r e (Table 5 . 2 )
also i n d i c a t e t h a t the 1:1 ( w h i t e ) and 2:1 ( 1 / 2 whole wheat) for mu la­
t io n s were s t a t i s t i c a l l y
f o r m u la t i o n .
(p < 0 . 0 5 )
pr e f e r r e d over the 2:1 (w h i t e )
Although there was no s t a t i s t i c a l
d i f f e r e n c e in the
rankings f o r prefere nc e (Table 5 . 2 ) , the order o f ranking in d ic a t e s
t h a t 2:1
2:1
( 1 / 2 whole wheat) was p r e f e r r e d , followed by 1:1 (w h i t e ) and
( w h i t e ) , the same order t h a t was found f o r t e x t u r e .
Since the chewy t e x t u r e was the p r i n c i p a l o b j e c t i o n of a m a j o r i t y
o f the p a n e l i s t s , an attempt was made to resolve the problem.
observed t h a t the 2:1
( 1 / 2 whole wheat) formu lat io n also had the lowest
i nt e rm ed ia te and f i n a l moisture c o n te n t, followed by the 1:1
and 2:1
I t was
( w hi te ) fo r m u la t i o n s .
(w h i t e )
Since moisture content o f foods
in flu en c es t e x t u r e , and most snack food products ( c h i p s , crac ker s,
etc.)
having moisture l e v e l s exceeding 3-3.5% lose crispness and become
unacceptable, i t was thought t h a t the 7-10% moisture content present in
the f r i e d product (Table 5 . 1 ) was having a negative a f f e c t on the
texture.
Fried samples of each f or m u la ti on were consequently d r i e d in
a vacuum oven f o r 20 hours a t 65°C and 30 psi to a f i n a l moisture
content of 3-4%, and were then presented to 12 members of the o r i g i n a l
panel who d i s l i k e d the t e x t u r e o f the f r i e d product.
the same score sheet format ( F i g .
They were given
5.2).
Results o f the sensory assessment of the t hre e formulations of the
d r ie d product are i n di c at ed in Table 5 . 3 .
No s t a t i s t i c a l
d i ff e r e n c e s
133
Table 5 . 3 .
Sensory e v a lu a t i o n of appearance, t e x t u r e , f l a v o r and
preference o f the th ree fo rm ul at io ns of the d r ie d product
(N = 12) .
Product
Appearance
Texture
Flavor
Mean
F
Sig.
1:1 ( w h i t e )
2:1 ( 1 / 2 whole wheat)
2:1 (w h i t e )
5.58
5. 08
5.92
4. 75
N.S.
1:1 (w h i t e )
2:1 ( 1 / 2 whole wheat)
2:1 ( wh it e)
5.25
5.75
5.33
1.97
N.S.
1:1 ( w h i t e )
2:1 ( 1 / 2 whole wheat)
2:1 ( w h i t e )
5.00
5:33
5.58
3.42
N.S.
Mean
X2
1.50
1.92
2.58
7.17
Product
Preference
1:1 (w h i t e )
2:1 ( 1 / 2 whole wheat)
2:1 ( wh it e)
N.S. represents not s i g n i f i c a n t .
lev el (p < 0 . 0 5 ) .
S tatistical
Si q
1 a
2 ab
3 b
d i f f e r e n c e is a t the 95%
134
were found f o r appearance, t e x t u r e or f l a v o r between the t hr ee
f o r m u l a t i o n s , and a l l
mean values are 5 or above.
Histograms o f the
number o f responses f o r each score ( F ig s . 5 . 8 - 5 . 1 0 ) furthermore
indicate th a t fo r a l l
t h r ee formulations and or gan ole pti c
c h a r a c t e r i s t i c s the m a j o r i t y o f responses l i e a t the " l i k e " end ( r i g h t
side ) o f the hedonic s ca le .
of the f r i e d product ( F i g .
A comparison o f the histogram f o r t e x t u r e
5 . 6 ) with t h a t o f the dried product ( F ig .
5 . 9 ) also shows t h a t a la r g e improvement in t e x t u r e was achieved by
f i n i s h - d r y i n g the product.
the 2:1
( w h i t e ) and 2:1
s tatis tic a lly
(p < 0 . 0 5 )
the d r ie d product.
Rank ana lys is (Table 5 . 3 ) i n d ic a t e s t h a t
( 1 / 2 whole wheat) fo rmulations were
p r e f e r r e d over the 1:1
(wh it e) fo r m u la t io n f o r
However, since no s t a t i s t i c a l
d i f f e r e n c e s were
found f o r appearance, t e x t u r e , or f l a v o r , the reason f o r the panel
preference cannot be determined from the sensory e v a lu a ti o n .
F i n i s h - d r y in g o f the product presents an a d d it io n a l processing
step r e s u l t i n g in a d d i t i o n a l
industrial
cost during production.
However, on an
le v e l the in te rm ed ia t e moisture content of the extruded
product could be c o n t r o l l e d so t h a t the moisture content o f the f r i e d
product would be low enough to provide an acceptable product.
A
r e l a t i v e l y high i nt e rm ed ia te moisture content (12-15%) is r eq ui re d when
using the experimental e x t r u d e r due to the overheating and clogging
t h a t occurs.
O bj e ct iv e Textural Determinations
The t e x t u r a l data f o r the f r i e d and d r ie d products are shown in
Table 5 . 4 (Appendix Tables 4.1 and 4 . 2 ) .
The three formulations of
135
TRERT. 1
TRERT. 2
TRERT. 3
2
3
M
B
7
SCORES
Fig.
5.8.
Appearance o f the dr ied product.
T r e a t 1 = 1:1 ( w h i t e ) ,
T r e a t . 2 = 2:1 ( 1 / 2 whole wheat), T r e a t . 3 = 2:1 ( w hi te .
Arrows po in t to treatment means.
TREHT. I
TREHT. 2
A
TREHT. 3
r-L
f
I
2
3
H
5
B
7
KTJRE5
Fig.
5.9.
Texture o f the dr ie d product.
Treat. 1 =
( w h i t e ) , T r e a t . 2 = 2:1 ( 1/ 2 whole wheat),
T r e a t . 3 = 2:1 ( w h i t e ) .
Arrows point to
treatment means.
TREHT. I
TREHT. 2
TREHT. 3
2
3
M
5
5
7
5<URE5
g.
5. 1 0 .
Flavor o f the dried product.
Treat 1 = 1
( w h i t e ) , T r e a t 2 = 2:1 ( 1 / 2 whole wheat),
T r ea t 3 = 2 : 1 ( w h i t e ) .
Arrows point to
tre atment means.
Instron Universal Testing Machine with a
0.5 in/min and a relaxation period of 1 min.
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Textural data for the dried products using the
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f r i e d product were s i g n i f i c a n t l y
(p < 0 . 0 1 )
less b r i t t l e and harder
than the d r i e d products, which supports the sensory d i f f e r e n c e s found
f o r t e x t u r e and also i n d ic a t e s why a l a r g e po rt io n of the panel may
have d i s l i k e d the t e x t u r e .
The f r i e d products also tended to compress
s l i g h t l y more than the d r ie d samples, and were more springy and
demonstrated more cohesiveness, which suggests a more chewy consistency
and may as well
have co n tr i b u t e d to the panel d i s l i k i n g the t e x t u r e of
the f r i e d product.
The high cohesiveness score f o r the 2:1 ( w h i t e )
f r i e d product, and the low cohesiveness score f o r the dried 2:1
(w h i t e )
product may be the reason the panel scored the f r i e d product
s i g n i f i c a n t l y i n f e r i o r f o r t e x t u r e , while the d r ie d product was ranked
s i g n i f i c a n t l y superior.
The low hardness, springiness and cohesiveness scores f o r the 2:1
( 1 / 2 whole wheat) f r i e d product, which were not s t a t i s t i c a l l y d i f f e r e n t
from the scores f o r a l l
t h r ee formulations o f the d r ie d product may be
the reason t h a t the t e x t u r e o f the whole wheat f r i e d product was
s i g n i f i c a n t l y pr ef er r ed by the panel at the f i r s t t a s t i n g .
Summary
A new potato/wheat snack was formulated by e x t r us io n.
The
extruded product was d e e p - f a t f r i e d to a golden colored f i n i s h e d
product.
The f in i s h e d product had an o i l
content of approximately 15%,
a 3-4% moisture content, and a gr anu lar appearance.
The s u b je c ti v e
ev a lu a ti o n o f t h i s snack i n d ic a t e d f av or abl e responses f o r appearance,
t e x t u r e and f l a v o r .
140
The combination of potato and wheat makes t h i s product a b e t t e r
q u a l i t y p r o t e i n snack than potato chips and f r i e s .
r e t a i n s less o i l
(15%) than chips or f r i e s
(30-40%).
Also, the new snack
The manufacture
o f t h i s potato/wheat snack should be e a s i l y adaptable to snack food
processing l i n e s in i n d u s t r y , and the f i n i s h e d product can be sold
e i t h e r as a base product or w it h a v a r i e t y o f f l a v o r i n g s .
141
Appendix Table 1 . 1 .
The e f f e c t of magnesium
f e r t i l i z a t i o n on the y i e l d
o f Katahdin potatoes grown
during two seasons.
Y i e l d (cwt/A)
MgS04 ( l b s / A )
Appendix Table 1 . 2 .
Year 1
Year 2
0
468
414
20
492
424
40
487
405
100
441
406
The e f f e c t of magnesium f e r t i l i z a t i o n on the
d i s c o l o r a t i o n o f Katahdin potatoes grown during two
seasons.
D i s c o lo r a t i o n (Rd)
Year 1
MgSC4 (Lbs/A)
Year 2
18.00 ± .10
16.80
± .99
20
18.30 ±
.76 ( N . S . )
19.27
±1.29
40
20.17
±
.35 (p < 0 . 0 1 )
20.17
± .87 (p < 0. 0 5 )
19.47 ±
.47 (p < 0 . 0 1 )
19.67
± .90 (p < 0. 0 5 )
0
100
Data represents an average of 3 values ± S.D.
Rd increases as d i s c o l o r a t i o n decreases.
NS represents not s i g n i f i c a n t .
142
Appendix Table 1 . 3 .
The e f f e c t o f magnesium f e r t i l i z a t i o n on the
phenolic content o f Katahdin potatoes grown during
two seasons.
Phenolic Content (mg/100 <3 F.W. .)
Year 1
MgS04 ( l b s / A )
0
69 .79 ±
Year 2
68.,30 + 1.84
.46
20
57 .00 + 1.41
40
52 .79 ± 1.69 (P < 0.01
100
58 .58 ±
(P < 0 . 0 1 )
.08 (P < 0 . 0 1 )
59..15 + 2.05
(P < 0 . 0 5 )
59..15 ± 2.90 (P < 0 . 0 5 )
55.,20 ± 1.41
(P < 0 . 0 5 )
Data represents an average o f 2 values1 ± S.D.
Appendix Table 1 .4 .
The e f f e c t o f magnesium f e r t i l i z a t i o n on the crude
l i p i d content o f Katahdin potatoes grown during two
seasons.
Crude L ip id (mg/q D.W.)
MgS04 ( l b s / A )
Year 1
Year 2
6.97 ± .04
7 . 4 4 ± .14
20
6.97 ± .05 (N.S.
7.67 ± .03 ( N . S . )
40
7.51 ± .02 (p < 0 . 0 1 )
9. 04 ± .09 (p < 0 . 0 1 )
100
7. 65 ± .04 (p < 0 . 0 1 )
9. 08 ± .08 (p < 0 . 0 1 )
0
Data represents an average of 2 values ± S.D.
significant.
N.S. represents not
143
Appendix Table 1 . 5 .
The e f f e c t of magnesium f e r t i l i z a t i o n on the phos­
p h o l i p i d content of Katahdin potatoes grown during
two seasons.
Phospholipid (mg/g D.W.)
MgS04 ( l b s / A )
Year 1
0
Year 2
2.65 ± .04
2 . 9 8 ± . 04
20
3.11 ± .09 (p < 0 . 0 1 )
3 . 0 7 ± . 01 ( N . S . )
40
3.33 ± .05 (p < 0. 0 1 )
3. 86 ± . 01 (p < 0 . 0 1 )
100
3.15 ± .07 (p < 0. 0 1 )
3.87 ± . 01 (p < 0 . 0 1 )
Data represents an average o f 2 values ± S,.D.
significant.
Appendix Table 1 . 6 .
Year
represents not
The e f f e c t o f magnesium f e r t i l i z a t i o n on the f a t t y
acid composition of Katahdin potatoes grown during
two seasons.
Fa tty Acid
{% )
MgSO.
(lbs/A)
16:0
18:0
18:2
18:3
0
22.00 ± 1.73
6 . 2 5 ± .51
44.46 ± 2.05
27.26 ± 1.89
20
25.39 ± .17
(N.S.)
6. 25 ± .01
(N.S.)
35.48 ± 1.30
(p < 0 . 0 1 )
32.46 ± 1.42
(p < 0 . 0 1 )
40
21.66 ± .79
(N.S.)
6.11 ± .82
(N.S.)
37.40 ± .55
(p < 0 . 0 1 )
35.38 ± 1.75
(p < 0 . 0 1 )
20.42 ± 1.84
(N.S.)
7 . 0 0 ± .09
(N.S.)
38.01 ± .26
(p < 0 . 0 1 )
33.89 ± 1.66
(P < 0 . 0 1 )
0
22.03 ± 1.48
5.80 ± .26
42.97 ± 1.11
28.07 ± 1.45
20
25.57 ± 1.31
(N.S.)
5.93 ± .59
(N.S.)
43.10 ± 1.08
(N.S.)
25.70 ± 0.70
(N.S.)
40
22.87 ± 1.37
(N.S.)
5. 43 ± .31
(N.S.)
43.53 ± 1.62
(N.S.)
27.47 ± 1.53
(N.S.)
100
23.50 ± .46
(N.S.)
5.43 ± .49
(N.S.)
43.73 ± 1.74
(N.S.)
27.27 ± 1.15
(N.S.)
1
100
2
N.S.
Data represents an average o f 2 values ± S.D.
significant.
N.S.
represents not
144
Appendix Table 1 . 7 .
Year
1
2
3
The e f f e c t o f MgSO. f e r t i l i z a t i o n on the t o t a l
n i t r o g e n , non -protein nitrogen and p r o t e i n content
o f Katahdin potato tu be rs .
MgSO^
Total Nit ro gen 9
Non-Protein Nit ro gen 9
Protein
(lbs/A)
(mg/gD.W.)
( m g /g D .W . )
(%)
16.17 ± .01
8 . 2 8 ± .11
5.95
40
18.06 ± . 0 6 b
9.11 + . 0 7 b
6.71
100
18.07 + . 0 7 b
8 . 6 9 ± . 08 ( N . S . )
7.05
0
0
18.75 + .25
10.94 + .16
40
20.00 + . 18c
9.4 0 ± . 26b
7.99
100
19.95 + . 17c
8.98 + .23b
8. 23
15.79 ± .02
8.01 ± .12
5.84
40
16.39 + . 0 2 b
7. 18 + . 29c
6.91
100
16.96 + . 0 4 b
7.76 + .07 ( N . S . )
6. 90
0
a.
Values presented as an average o f 2 values ± S.D.
b.
S i g n i f i c a n t a t 99% le v e l
(p < 0 . 0 1 ) .
c.
S i g n i f i c a n t a t 95% le ve l
(p < 0 . 0 5 ) .
N.S.
5.86
represents not s i g n i f i c a n t .
145
Table 2 . 1 .
The e f f e c t o f MH on t h e t o t a l n i t r o g e n , n o n - p r o t e i n n i t r o g e n
and p r o t e i n c o n t e n t s o f c o r t e x and p i t h p o t a t o t i s s u e (MH a t
0 and 3 l b s / a c r e ) .
Total Nitrogen
(mg/g D.W.)
L .I.
Non-Protein Nitrogen
(mg/g D. W.)
Pro te in
(%)
Katahdin
CX
+MH
Si g.
18.94 ±
19.63 ±
N.S.
.56
.33
9. 14 ± .18
9.47 ± .11
N.S.
7.37
7.62
Pi
+MH
Si g
19.72 ± 1.02
22.53 ± .01
p < 0.01
10.16 ± .16
13.58 ± .16
p < 0.01
7. 17
6.71
Cx
+MH
Sig.
16.50 ± .13
18.32 ± .04
p < 0.01
9.89 ± .19
11.46 ± .09
p < 0.01
4.95
5.15
Pi
+MH
Sig.
20.08 ± .01
19.76 ± .73
N.S.
13.33 ± .27
13.28 ± .16
N.S.
5.06
4. 88
Cx
+MH
Sig.
16.21 ± .21
19.67 ± .36
p < 0.01
6.8 5 ± .08
9.61 ± .18
p. < 0.01
7.0 2
7.5 5
Pi
+MH
Sig
17.64 ± .40
18.13 ± .40
N.S.
9.61 ± .18
9.41 ± .13
N.S.
6. 02
6.54
Ithaca Katahdin
Itha ca Kennebec
Data represents an average o f 2 values ± S.D.
significant.
N.S. represents not
146
Tab le 2 . 2 .
The e f f e c t o f MH on th e t o t a l n i t r o g e n , n o n - p r o t e i n n i t r o g e n
and p r o t e i n c o n t e n t s o f c o r t e x t i s s u e o f Ka tah din p o t a t o e s
(MH a t 0 , 3 , 6 and 9 l b s / a c r e ) .
Male ic Hydrazide
(lbs/acre)
Total Nitrogen
(mg/g D.W.)
Non-Protein Nitrogen
(mg/g D.W.)
Prot ei n
(% )
0
17.94 ± .02
8.01 ± .08
7.45
3
17.99 ± .09
(N .S .)
7 . 8 8 ± .26
(N.S.)
7.5 8
6
18.62 ± .22
(p < 0 . 0 1 )
8 . 5 0 ± .03
(N.S.)
7.59
9
19.35 ± .88
(p < 0 . 0 1 )
9.17 ± .06
(p < 0 .0 1)
7. 6 4
Data represents an average o f 2 values ± S.D.
significant.
Appendix Table 2 . 3 .
N.S. represents not
The e f f e c t of CIPC on the t o t a l n i tr o g e n ,
non-p ro te in nitrogen and p r o t e i n contents o f cortex
and p i t h tissues o f Katahdin potatoes.
Total Nitrogen
(mg/g D.W.)
Non-Protein Nitrogen
(mg/g D.W.)
Protein
(*)
Cx
17.23 ± .07
9 . 1 4 ± .13
6.07
+CIPC
17.16 ± .13
8 . 9 2 ± .09
6.18
N.S.
N.S.
Pi
19.64 ± .10
12.57 ± .19
5.29
+CIPC
19.99 ± .31
13.24 ± .22
5.06
N.S.
N.S.
Sig.
Sig.
Data represents an average o f 2 values ± S.D.
significant.
N.S. represents not
147
Appendix Table 3 . 1 .
The e f f e c t of cooking method on the t o t a l n i tr o g e n ,
non -protein ni tro ge n and pr o t e i n contents of cortex
and p i t h potato t i s s u e .
Total Ni trogen3
(mg/g D.W.)
Non-Protein Nitqro genb
(mg/g D.W.)
14.41 ± .28
7.41 ± .35
5.25
Conventional
Sig.
13.85 ± .11
p < 0.05
7.62 ± .30
N.S.
4. 67
Microwave
Sig.
14.19 ± .03
N.S.
7.58 ± .07
N.S.
4. 96
Control
15.53 ± .09
10.74 ± .28
3. 89
Conventional
Sig.
17.67 ± .18
p < 0.01
12.84 ± .21
p < 0.01
3. 62
Microwave
Sig.
13.44 ± .21
p < 0.01
8.86 ± .42
p < 0.01
3.44
Cx
Control
Protein
(%)
f i
a.
Data represents an average o f 3 values ° S.D.
b.
Data represents an average o f 2 values ± S.D.
N.S.
represents not s i g n i f i c a n t .
Instron
Universal
148
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Table
4.1.
Textural ch a ra cte ristics
Testing machine.
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150
S tatistical
Analysis on the Data Presented in Appendix Tables 4.1 and 4. 2
LSD
F
Sig.
Brittleness
26 .1 0
P < 0.01
1
2
3
6
4
5
Hardness
15.99
P < 0.01
1
3
2
4
6
5
Compression
1.86
Springiness
9.99
P < 0.01
1
3
2
5
4
6
27. 83
P < 0.01
3
1
2
5
4
6
Cohesiveness
N.S.
1 = 1:1 ( w h i t e - d r i e d ) ; 2 = 2:1 ( 1 / 2 whole w h e a t - f r i e d ) ; 3 = 2:1
f r i e d ) ; 4 = 1 : 1 ( w h i t e - d r i e d ) ; 5 = 2:1 ( 1 / 2 whole w h e a t - d r i e d ) ;
6 = 2:1 ( w h i t e - f r i e d ) .
(white-
LIST OF REFERENCES
Adams, P . , J. N. Davies and G. W. Winsor.
1978.
Effects of nitrogen,
potassium and magnesium on the q u a l i t y and chemical composition of
tomatoes grown in peat.
J. Hort . S c i . 53:11 5-1 22.
Adams, P . , C. J. Graves and G. W. Winsor.
1978a.
Some responses o f
l e t t u c e , grown in beds o f pea t, to n i t r o g e n , potassium, magnesium
and molybdenum.
J. H o rt . Sci. 5 3 ( 4 ) : 2 7 5 - 2 8 1 .
Adams, P . , C. J. Graves and G. W. Winsor.
1788b.
Tomato y i e l d s in
r e l a t i o n to the n i t r o g e n , potassium and magnesium st at us o f the
pla nt s and o f the peat su b s tr a t e .
P la n t and Soil 44 9 :1 37 -1 48 .
AOAC.
1975.
O f f i c a l Methods of A n a ly s is , 12th ed.
A n a l y t i c a l Chemists, Washington, DC.
Assoc, o f O f f i c i a l
Ashford, N. and J. L e v i t t .
1965.
R e la ti on o f su lf hy dr yl
in potato t ub er s.
P h ys io l. P la n t a. 18: 229-239.
groups to re st
Augustin, J . , S. R. Johnson, C. T e i t z e l , R. H. True, J. M. Hogan, R. B.
Toma, R. L. Shaw and R. M. Deutsch. 1978.
Changes in the n u t r i e n t
composition o f potatoes during home p r e p a ra ti o n .
I I . Vitamins.
Amer. Potato J. 55:6 5 3- 6 62 .
Augustin, J . , R. B. Toma, R.
H. True, R. L. Shaw, C. T e i t z e l , S. R.
Johnson and P. Orr.
1979. Composition o f raw and cooked potato
peel and f l e s h :
Proximate and vi ta mi n composition.
J. Food Sci.
44: 80 5-8 06.
Bartolome, L. G. and J. E. H o ff .
1972.
Biochemical e f f e c t s o f preh ea ting .
Firming of potatoes:
J. Agr. Food Chem. 20:26 6-2 70.
Bo lto n, J.
1977.
Liming e f f e c t s on the response of potatoes and oats
to phorphorus, potassium and magnesium f e r t i l i z e r s .
J. A g r i c .
S c i . , Camb. 8 9 : 8 7 - 9 3 .
Bourne, M. C. and N. I . Mondy.
1967.
Measurement of whole potato
firmness with a Universal Testing Machine.
Food Technol.
2 1( 10 ) :97.
Bowman, F . , E. P. Berg, A. L. Chuang, M. W. Gunther, D. C. Trump and K.
Lorenz.
1975.
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