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A physiological and biochemical study of the curing processes in sweet potatoes

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A PHIS 10LOGICAL AND BIOCHEMICAL STUDY OF THE CURING
PROCESSES IN SWEET POTATOES
by
P e te r H.^Heinze
p
Thesis subm itted to th e F acu lty o f th e Graduate School
o f th e U n iv e rsity o f Maiyland in p a r t i a l
f u lf illm e n t of th e requirem ents f o r th e
degree of Doctor o f Philosophy
1940
UMI Number: DP70142
Alt rights reserved
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TABLE OF CONTENTS
Page
INTRODUCTION
1
REVIEW OFLITERATURE.................................................................................
2
ANALXTICAL
8
PROCEDURE..............................................................
M oisture
Sugars
. • . .
..........................................................
9
♦ ...... ....................... .................................................
9
S tarc h and d e x trin
H em icellulose
......................................................
9
.....................................................................
10
T o tal pectin * * ....................................................................... 11
S oluble p e c tin ............................................... * ....................... 12
P ro to p e c tin •
....................................
12
T o tal n itro g e n ........................................................................... 12
E x tra c tio n of n o n -p ro tein n itro g e n .................................. 12
T o tal n o n -p ro tein nitrogen*
........................
13
T o tal alpha-amino n itro g e n .................................................. 13
Basic n itro g e n .....................................................
Mono-amino n itro g e n
13
...................................... 14
.
Ammonia n itro g e n ..................... .............................................14
Amide n itro g e n
. . . . . . . . . . .
.....................
14
Humin n i t r o g e n ....................................................................... 15
R esidual n itro g e n . . . . . . . .
.............................
15
MATERIAIS AND EXPERIMENTAL PROCEDURE.....................................................15
EXPERIMENTAL RESULTS................................................................................... 16
Carbohydrate Transform ations in Sweet P otatoes during
....................
Curing and Storage
19
P e c tic Changes in Sweet P otatoes During Curing and
S to ra g e ....................................................................................25
44567
Page
E ffe c ts o f S torage in an Aqueous S o lu tio n on th e
S oluble N on-protein N itrogen F ra c tio n s . . . . . . 2 8
N itrogen Metabolism i n Sweet P o tato es During
Curing and S t o r a g e ............................. • ............................. 29
D is tr ib u tio n o f Nitrogenous Compounds in th e
Proxim al and D is ta l Halves of SweetP otatoes . .
39
D is tr ib u tio n o f Nitrogenous Compounds in th e Inner
and O uter p a r ts o f Sweet P o ta to e s .................................. 40
Comparative Keeping Q u ality of Sweet P o tato es Cured
under D iffe re n t Conditions . . . . . ....................
41
SUMMARY AND CONCLUSIONS........................................................................... 47
IITERATUKE CITED........................................................................................... 49
ACKNOWLEDGMENT................................................................................................53
INTRODUCTION
The sto ra g e o f sweet p o ta to e s has long been one o f th e most se rio u s
problems c o n fro n tin g commercial sweet p o tato grow ers.
Losses ranging
from 20 to 30 p e rc e n t and sometimes as high as 50 p e rc e n t o f th e s to re d
crop are fre q u e n tly re p o rte d .
The g r e a te s t p o rtio n o f th e lo s s i s d i­
r e c t l y a ttr ib u te d to decay and p h y sio lo g ic a l shrin k ag e.
I f sweet p o ta to e s are t o be k ep t f o r any len g th of time in sto ra g e
th e y must be su b je c te d to a p re lim in a ry cu rin g p e iio d of 10 days to 2
weeks.
Elmer (13) s t a t e s t h a t th e optimum co n d itio n f o r cu rin g sweet
p o ta to e s i s a tem perature o f approxim ately 85°F. and a r e la tiv e hu­
m id ity o f 90 p e rc e n t.
Thompson e t a l . (43) compared sweet p o tato es
cured a t 75 and 85 °F. and a f t e r a p erio d o f sto ra g e found those cured
a t 75° F . contained a markedly low er p ro p o rtio n o f a t t r a c t iv e , high
grade r o o ts .
This in v e s tig a tio n has been concerned c h ie f ly w ith th e e f f e c t of
v a rio u s cu rin g c o n d itio n s on th e biochem ical changes t h a t occur dur­
in g th e c u rin g p ro cess and th e subsequent s to ra g e p erio d and th e pos­
s ib l e re la tio n s h ip s t h a t may e x is t between th ese changes and th e keep­
in g q u a lity of th e sweet p o ta to e s.
A study was made of some o f the
carbohydrate tra n sfo rm a tio n s t h a t occur, th e changes i n th e p e c tic
m a te r ia ls , and th e n itro g e n metabolism involving a d e ta ile d a n a ly s is
o f th e s o lu b le n o n -p ro tein n itro g e n .
z
REVIEW OF LUERATtJEE
The anatom ical in v e s tig a tio n s of McCormick (26) and Artschwager (7)
show t h a t th e fle s h y s to ra g e organs o f Ioomoea b a ta ta s are r o o ts .
In
t h i s re s p e c t th e sweet p o ta to d i f f e r s from th e I r i s h p o tato which i s a
tuber*
The sweet p o ta to i s extrem ely s e n s itiv e to th e tre atm e n t i t receiv es
and g r e a t p re c a u tio n must be observed during h a rv e stin g and th e l a t e r
h an d lin g i f la rg e lo s s e s are to be avoided.
Thompson and B e a ttie (42)
have compared th e keeping q u a lity of in ju re d and u n in ju re d sweet p o ta­
to e s o f th re e common v a r i e t ie s .
e i t h e r c u t o r b ru is e d .
Eveiy p o tato in th e damaged lo ts was
A fter 164 days of sto ra g e the average lo s s due
to shrinkage was 28.13 p e rc e n t o f th e o r ig in a l w eight f o r th e in ju re d
and 13.83 p e rc e n t f o r th e u n in ju re d .
The lo ss e s due to decay were
13*79 p e rc e n t f o r th e in ju re d and .75 p ercen t f o r th e u n in ju re d .
In
a l l cases th e in ju re d ro o ts o f th e Je rs e y v a r ie t ie s showed much h ig h er
lo s s e s th a n o th e r v a r i e t i e s .
Various sto ra g e tem peratures ranging from
50 t o 65° F . were a lso compared.
When both shrinkage and decay were
considered a sto ra g e tem perature o f 50 to 55° F. proved to be th e most
s a tis f a c to r y .
Manns (25) emphasized th e im portance of supplying s to re d sweet
p o tato es w ith p le n ty o f v e n t ila t io n .
He also showed t h a t allow ing
m oisture to c o l l e c t on th e p o ta to e s r e s u lts in a ra p id decay o f a l l
o f th e r o o ts .
Weimer and H arter (47) and Artschwager and S t a r r e t t (8) have shown
t h a t one o f th e p ro cesses o ccu rrin g during cu rin g i s th e fo m a tio n of
a wound periderm over th o se in ju re d areas th a t must n e c e s s a r ily occur
3
a t th e ends o f th e p o ta to .
The periderm liras found to develop most r e a d ily
a t r e l a t iv e h u m id ities o f 90 p e rc e n t o r above and a t tem peratures from 28.7
to 34.8 °C.
The form ation o f a wound cork periderm h elp s
to exclude v ario u s
m icroorganism s t h a t a re v e ry d e s tr u c tiv e to th e r o o ts .
H a rte r and Weimer (17) have shorn th a t v ario u s sp ecies o f Rhizopus p ro ­
duce a pow erful i n t r a c e l l u l a r and e x tr a c e llu la r p e c tin a se which d iss o lv e s
th e m iddle la m e lla so t h a t th e c e l l s o f th e sweet p o ta to r e a d ily s e p a ra te
and p ro v id e an e x c e lle n t source of nourishm ent f o r th e mycelium.
L au ritzen (24) s t a t e s t h a t sweet p o ta to e s are s u sc e p tib le , a t tempera­
tu r e s below 9 °C ., to in f e c tio n by v ario u s fu n g i -which do n o t norm ally appear
a t tem p eratu res above 9°C. and suggests th a t th i s may in d ic a te a change in
th e phy sio lo g y o f th e h o s t.
A c h illi n g in ju ry evidenced by in te r n a l brown­
in g a ls o appeared in th e ro o ts h e ld a t tem peratures below 9.5°C .
He con­
c lu d e s , "Taking in to c o n sid e ra tio n th e danger of both c h illin g in ju r y and
in f e c tio n , th e re i s n o th in g to commend even th e tem porary exposure of sweet
p o ta to e s to tem p eratu res below 10®C."
I t i s g e n e ra lly known t h a t sweet p o ta to e s become sw eeter to th e ta s te
as th e le n g th o f th e sto rag e p erio d in c r e a s e s .
H arrington (1 6 ), in 1895,
found t h a t sweet p o ta to e s i n sto ra g e from h a rv e st time u n t i l March in ­
creased in t o t a l su g a r c o n te n t as th e sto ra g e p erio d advanced.
S hiver (3 8 ),
i n 1901, found th a t s ta r c h g ra d u a lly decreased and cane sugar in cre a se d
d u rin g the s to ra g e p e rio d b u t t h a t th e reducing sug ars showed only s lig h t
changes*
N eith e r o f th e se in v e s tig a to r s d escrib e the cu rin g and sto ra g e
c o n d itio n s to which th e p o ta to e s were su b je c te d .
y
In a much more thorough
and e x te n siv e in v e s tig a tio n H asselbring and Hawkins (19) showed th a t the
m oisture c o n te n t rem ains f a i r l y c o n sta n t in sweet p o ta to e s sto re d a t a
tem perature of 11.7° t o 1 6 .7 °C. and t h a t a g rad u al disappearance of s ta rc h
4
occurs d u rin g th e season from October to March*
However, th e y noted a
disappearance o f cane su g ar accompanied by a probable reform ation o f s ta rc h
d u rin g th e l a t t e r p a r t o f th e sto ra g e p erio d (March to Ju n e), when appre­
c ia b ly h ig h e r tem p eratu res e x isted *
These same w r ite r s rep o rted t h a t sweet
p o ta to e s s to r e d a t low tem p eratures (4° C*) show a ra p id disappearance o f
s ta r c h and an accompanying in c re a s e i n cane su g a r.
An eq u ilib riu m i s n o t
reached because th e p o ta to e s in v a ria b ly r o t w ith in a s h o rt time under th ese
c o n d itio n s .
H asselbring and Hawkins (20) concluded t h a t i n th e carbohydrate
tra n sfo n n a tio n s i n s to re d sweet p o ta to e s s ta rc h i s f i r s t converted to re ­
ducing su g a rs th en cane su g ar i s sy n th esized from the reducing su g a rs.
The
r a te s of s ta r c h h y d ro ly s is and su g ar fo m a tio n were found to conform i n a
g e n e ra l way to th e V an 't Hoff tem perature r u le f o r chem ical r e a c tio n s .
At
h ig h e r tem p eratu res th e re a c tio n s are ra p id a t f i r s t , b u t soon become slow er
and approach an e n d p o in t.
At low tem peratures th e r a te s are slow er and th e
endpoint i s so s h if te d as t o p erm it a g r e a te r c o n c e n tra tio n of su g a r.
^ Hopkins and P h i l l i p s (22) found th e change i n sugar co n ten t o f sweet p o ta­
to e s w ith tim e i n s to ra g e t o be very uniform and constant*
This was demon­
s t r a t e d by p lo ttin g th e lo g o f th e p e rc e n t o f sucrose a g a in s t th e lo g of
th e tim e i n d ay s.
S tr a ig h t li n e s were o b tain ed from which th e y have deriv ed
eq u atio n s f o r th e r e a c tio n .
The e f f e c t o f tem perature on th e s ta rc h -s u g a r change i n s to re d I r i s h
p o ta to e s i s w e ll known.
MtLLler-Thurgau (28) and Appleman (3) have shown
t h a t th e e q u ilib riu m i s v e ry s e n s itiv e to tem perature changes.
Sugar ac­
cum ulates a t low tem p eratu res (0° to 6*C.) b u t ra p id ly d isap p ears and
s ta r c h in c re a s e s when th e p o tato es are p laced in a h ig h er sto ra g e tempera­
tu r e ( 8 ° to 10 °C •) *
5
Anderson ( l ) and K e itt (23) re p o rt t h a t th e p e rc e n t o f s ta rc h i n th e
sw eet p o ta to g ra d u a lly in c re a s e s and th e p e rc e n t o f m oisture and t o t a l
su g ars g ra d u a lly d ecrease as th e growing season advances.
Thus th e h ig h e st
s ta r c h c o n te n t e x is ts a t about h a rv e s t tame o r s h o r tly b e fo re .
The ra p id
h y d ro ly s is o f s ta r c h to su g ar a f t e r h a rv e st has become of g r e a t concern to
th o se i n t e r e s t e d in th e commercial production o f s ta r c h from sweet p o ta to e s .
This i s evidenced by th e re p o rt o f Paine e t a l . (31) i n which a method of
ra p id d ry in g i s proposed to p rev en t th e lo s s of s ta r c h .
D astu r and A g n ih o tri (12) have stu d ie d th e p e c tic changes in th e I r i s h
p o ta to tu b e rs a t d if f e r e n t s ta g e s o f growth and during th e s to ra g e p e rio d .
They determ ined th e f r e e soluhLe p e c tin , p ro to p e c tin , middle la m e lla p e c tin ,
and t o t a l p e c tin .
The f r e e so lu b le f r a c tio n was found to in c re a se w ith the
advance o f th e s to ra g e p e rio d and decay o f th e tu b e r s .
d ecrease was n o ted i n th e o th e r f r a c tio n s .
A corresponding
S o ften in g of th e tu b e rs was
a t t r i b u t e d la r g e ly to th e lo s s o f middle la m e lla p e c tin and p ro to p e c tin .
W hite-Stevens (48) in v e s tig a te d th e d i f f e r e n t p e c tic c o n s titu e n ts in
c e le r y d uring c o ld s to ra g e .
He found no d e f in ite c o r re la tio n between
p e c tic h y d ro ly sis and s to ra g e m a tu rity except when sto ra g e pathogenes in ­
duced c y to ly tic e f f e c t s .
Rosa (36) in h is work on th e changes in com position during rip e n in g
and s to ra g e o f melons noted th a t th e t o t a l p e c tic m a te ria l remaired con­
s t a n t during rip e n in g on th e v in e b u t a s li g h t lo s s w3s found when th e
melons were rip e n e d i n s to ra g e .
In both cases a tra n sfo rm atio n o f p ro to ­
p e c tin to p e c tin took p la c e during th e rip e n in g and s o fte n in g o f th e
fle s h .
E lw e ll and Dehn (14) have given d a ta on th e co n c e n tra tio n o f th re e
p e c tic f r a c tio n s i n v a rio u s v eg etab les and o th e r p la n ts .
The la c k o f
6
d e s c rip tio n o f th e m a te r ia l and th e lim ite d in fo rm atio n concerning t h e i r
methods makes th e d a ta o f l i t t l e v alu e f o r comparison.
They r e p o rt the
p e c tic c o n te n t o f sw eet p o ta to e s a t 3*45 p e rc e n t o f th e f re s h weight*
P a rk e r and S tu a r t (32) determ ined th e t o t a l p e c tih , so lu b le p e c tin ,
and p ro to p e c tin i n h a rv e ste d green snap beans during s to ra g e .
Large
beans were found to c o n ta in more so lu b le p e c tin than sm all beans b u t
th e s o lu b le p e c tin in c re a se d in bo th during co ld s to ra g e .
A sy n th e sis
o f p ro to p e c tin caused an in c re a se in th e t o t a l p e c tic substances during
s to r a g e •
Appleman and Conrad (5 ), in a stu d y of th e p e c tic c o n s titu e n ts of
tom atoes, found p ro to p e c tin to predom inate in th e green m ature tomato
b u t a ra p id tra n sfo rm a tio n o f p ro to p e c tin to p e c tin occurred as th e
tom atoes reached a f u l l rip e s ta g e .
N ig h tin g ale e t a l . (30) found t h a t sweet p o ta to e s a t h a rv e s t tim e
co n tain ed as high as 65 p e rc e n t o f t h e i r t o t a l n itro g e n in th e so lu b le
n o n -p ro te in form .
Gruntuch (15) and Rahn (34) e a r l i e r rep o rted t h a t
such underground s to ra g e organs as r o o ts , tu b e r s , and bulbs have a
c h a r a c t e r i s t i c a l l y h igh amount of t h e i r n itro g e n in th e form o f so lu ­
b le compounds.
S tu a r t and Appleman (39) have shown th a t th e d is tr ib u tio n o f th e
v ario u s n itro g e n f r a c tio n s rem ained v ery c o n sta n t in th e I r i s h p o ta to
tu b e r f o r sto ra g e p e rio d s up to f iv e months.
They found t h a t th e n i t r o ­
gen f r a c tio n s v a rie d co n sid e rab ly in d if f e r e n t p a r ts o f th e tu b e r.
The
m edulla co n tain ed as high as 61 p e rc e n t of i t s t o t a l n itro g e n in the
so lu b le n o n -p ro te in form as compared to 49 p e rc e n t in th e c o r t ic a l t i s ­
sue.
They a lso rep o rte d t h a t th e re v e rsio n of parenchymatous c e lls to
embryonic c e l l s of th e new cork cambium in c u t tu b ers was accompanied
7
by an in c re a s e in p r o te in and b a s ic n itro g e n a t th e expense o f th e amino
n itro g e n .
The amide f r a c tio n remained f a i r l y c o n s ta n t.
Thus they con­
cluded t h a t amino ac id s r a th e r th an amides are concerned in th e regener­
a tio n o f p ro te in s*
Appleman and M3H e r (6) observed t h a t h y d ro ly sis o f p ro te in i s one
o f th e im p o rtan t rip e n in g and m aturing p ro cesses in I r i s h p o ta to e s .
Appleman (4) n o ted t h a t th e seed and stem end o f th e p o ta to d iff e r e d in
t h e i r n itro g e n c o n te n t and i n th e fona o f n itro g e n .
He also d e te c te d
in c re a s e s i n th e s o lu b le n itro g e n f r a c tio n s a f te r sp ro u tin g occurred.
Andre (2) analyzed th e ex p ressed ju ic e of two v a r ie tie s o f p o tato es
du rin g th e s to ra g e p e rio d from O ctober u n t i l May.
He determ ined th e
t o t a l n itro g e n , th e n itro g e n t h a t p assed through a co llo d io n membrane,
and th e n itro g e n co ag u lated by h e a t.
Each f r a c tio n was found to i n ­
c re a se w ith th e age o f the p o ta to .
S tu a r t and Appleman (39) found t h a t d iffe re n c e s up to 4 .5 p e rc e n t
in th e m o istu re c o n te n t o f I r i s h p o ta to e s caused by d if f e r e n t sto ra g e
co n d itio n s had no a p p re c ia b le e f f e c t on th e n itro g e n m etabolism during
s to r a g e .
I t i s im possible to rev iew here a l l th e work d e a lin g w ith th e me­
tab o lism o f th e v a rio u s n itro g e n f r a c tio n s in p l a n ts .
The re c e n t ex­
te n s iv e review s by Robinson (3 5 ), N ightingale (2 9 ), and McKee (27)
p r a c t i c a l l y b rin g up to d a te th e p re s e n t knowledge o f th e p h y s io lo g ic a l
r o le o f n itro g e n i n p la n ts .
The o r ig in and fu n c tio n o f amides has remained in q u estio n sin c e
t h e i r d isco v e ry i n p la n t t i s s u e s .
C hibnall (11) i n h is t r e a t i s e of
p r o te in m etabolism i n p la n ts , d isc u sse s in co n sid erab le d e t a i l amide
m etabolism .
According to h is conception carbohydrates undergo tr a n s ­
8
fo rm atio n s to 3-carbon p ro d ucts from -which o x a la c e tic and di k e to g lu ta ric
a c id s a re form ed.
These a c id s r e a c t w ith ammonia to give th e two most
commonly o c c u rrin g am ides.
C hibnall (10) found n i t r i c n itro g e n and mono­
amino n itro g e n to v ary d i r e c t ly -with th e p ro te in co n te n t in th e leav es
o f ru n n er bean p la n ts*
■with p r o te in s y n th e s is .
T h is, he sa y s, in d ic a te s th e y may be connected
In s ta r v a tio n experim ents he found t h a t aspara­
g in e n itro g e n rem ained unchanged.
From t h i s he concludes t h a t aspara­
gine i s n o t d eriv ed from th e decom position o f th e l e a f p r o te in s .
Thompson (41) n o ted t h a t amino n itro g e n accum ulates in c e le ry when
i t i s exposed to low tem perature tre a tm e n t.
Harvey (18) rep o rte d th a t
co ld tre a tm e n t o f cabbage p la n ts caused an in c re a se i n amino n itro g e n
c o n te n t.
V ickery and Pucher (44) have shown t h a t by v arying th e n u tr ie n t
s o lu tio n th e ammonia co n ten t o f tobacco leav es may range from S .25 p er­
c e n t to as much as 10.3 p e rc e n t of the s o lu b le n itro g e n w hile th e amide
n itro g e n rem ains e s s e n t i a l l y unchanged.
Piianischnikow and Schulow (33)
i n 1910 advanced th e h y p o th esis t h a t an im portant fu n c tio n o f amides
was t o p rovide a means o f m ain tain in g a low le v e l in th e ammonia con­
t e n t which m ight o th erw ise become to x ic .
V ickery and Pucher (44) s t a t e
t h a t t h i s h y p o th esis does n o t e x p la in th e co n d itio n s e x is tin g in rhubarb
and tobacco le a v e s .
ANALYTICAL PROCEDURE
A l o t o f s i x re p re s e n ta tiv e sweet p o ta to e s c o n s titu te d a sample
f o r a n a ly s is .
The ro o ts were washed and allowed to d ry f o r about 30
m inutes in th e la b o ra to ry .
Then th e y were passed through a Nixfcamal
m ill and th e pu lp thoroughly mixed.
9
M o istu re.
A ip lic a te samples o f th e pulp approxim ating 5 g . each
■were p lac ed between ta r e d watch g la s s e s , clanged to g e th e r, weighed im­
m e d ia te ly , and d rie d to a c o n sta n t w eight i n a vacuum e q u iv alen t to 30
in ch es o f m ercury, a t a tem perature o f 80 °C.
S u g ars.
D u p licate samples of 25 g . each o f th e pulp were weighed
i n t o co u n terp o ised 200 m l. Kohlrauch sugar f la s k s and imm ediately covered
w ith 75 m l. o f b o ilin g 95 p e rc e n t a lc o h o l.
The samples were placed on
a steam b a th and 50 m l. o f b o ilin g w ater added.
The s o lu tio n s were kept
b o ilin g v ery g e n tly and th e e x tr a c tio n continued f o r 30 m inutes.
Glass
bulbs blown from th ic k w alled tu b in g served as sm all condensers f o r th e
f la s k s .
a lc o h o l.
The f la s k s were removed and made to volume w ith 95 p ercen t
An a liq u o t o f th e f i l t e r e d e x tr a c t was evaporated on th e
steam b a th .
A few m l. o f w a te r were added from tim e to tim e and th e
ev ap o ratio n continued u n t i l no odor o f alco h o l could be d e te c te d . The
s o lu tio n s were c l a r i f i e d w ith le a d a c e ta te , deleaded, and made to vol­
ume.
The reducing sugars were determ ined by a m o d ificatio n o f th e
Shaffer-Som ogyi semi-m icro method (2 1 ).
For t o t a l sugars a 50 m l.
a liq u o t o f th e c le a re d e x tr a c t was hydrolyzed w ith 5 m l. of concen­
t r a t e d h y d ro ch lo ric a c id (sp . g r . 1.178) f o r 10 hours a t a tempera­
tu r e o f 35 °C.
p le
The s o lu tio n was made to volume, a p o rtio n o f th e sam­
n e u tra liz e d w ith anhydrous sodium carbonate, and th e sugar d e te r­
mined as d e scrib ed f o r reducing su g a rs.
S ta rc h and D e x trin .
For th e s ta rc h and d e x trin d eterm inations
25 g . of pulp were weighed in to a 250 m l. Erlenmeyer f la s k and covered
w ith 125 m l. o f co ld 95 p e rc e n t a lc o h o l.
At th e tim e o f a n a ly s is th e
s to ra g e alco h o l was removed in a Buchner fu n n el.
The pulp was washed
w ith 80 p e rc e n t a lc o h o l u n t i l f r e e o f sugars as in d ic a te d by th e
10
M olisch t e s t .
A fte r washing w ith e th e r th e pulp was d rie d and ground to
p a ss a 60 mesh sie v e i n a micro—Vfiley- m ill*
Hie ground m a te ria l was
d r ie d to a c o n s ta n t w eight i n a vacuum oven a t 80 °C.
One gram of the
d r ie d m a te r ia l was used f o r s ta r c h and d e x trin d eterm in atio n .
About 100
m l. o f b o ilin g w ater were added to th e s ta rc h and d e x trin sample and
th e m ixture b o ile d g e n tly f o r 15 minutes to g e la tin iz e th e s ta r c h .
It
was th en cooled to 45°C ., 10 m l. o f f r e s h ly c o lle c te d , d ilu te d s a liv a
(1 :4 and f i l t e r e d ) were added, and th e tem perature m aintained a t 45°C.
f o r one h our.
The s o lu tio n was b o ile d , cooled, and again d ig e ste d w ith
s a liv a u n t i l no f u r th e r in d ic a tio n of th e presence of s ta rc h could be
d e te c te d w ith th e io d in e t e s t .
The s o lu tio n was f i l t e r e d in to a 250
m l. volu m etric f la s k , made to volume, and a 200 ml. a liq u o t removed
and hydrolyzed w ith 12.5 m l. of co n cen trated h y drochloric ac id f o r 2*5
h o u rs.
Follow ing h y d ro ly sis th e s o lu tio n was cooled and tra n s f e rr e d
to a 500 m l. volu m etric f la s k and made to volume.
The s o lu tio n s were
n e u tr a liz e d and th e reducing v alu es determ ined as f o r the su g a rs.
The d e x trin s were determ ined by e x tra c tin g 5 g . of th e d rie d ma­
t e r i a l w ith 300 m l. o f w ate r f o r 1 hour on a m echanical sh ak er.
A fter
e x tr a c tio n th e samples were f i l t e r e d , a 200 m l. a liq u o t was hydrolyzed
w ith 1 2 .5 m l. o f c o n ce n tra ted h y d ro ch lo ric acid f o r 2.5 h o u rs, and the
reducing power determ ined as f o r th e s ta r c h and d e x trin sample.
The percen tag e o f s ta r c h was estim ated by s u b tra c tin g th e p e rc e n t­
age o f d e x tr in from th e percentage o f s ta rc h and d e x tr in .
Henri c e l l u l o s e .
The in so lu b le re sid u e rem aining a f t e r s ta r c h d i­
g e s tio n was p lac ed i n a d ig e s tio n f la s k w ith 200 m l. of w ater, 12.5 ml.
o f co n ce n trate d h y d ro ch lo ric a c id were added, and th e pulp hydrolyzed
f o r 2 .5 hours under r e f lu x condensers.
The s o lu tio n was f i l t e r e d and
11
made "bo volume*
A p o rtio n was n e u tra liz e d and th e reducing v alues d e te r­
mined as f o r th e p revious m ateria ls*
The reducing substances secured by
t h i s tre a tm e n t were term ed h em icellulose •
T o tal P e c tin * D u p licate samples of 50 grams of th e f r e s h ly ground
pulp were weighed in to co u nterpoised Erlenmeyer f la s k s and covered w ith
260 ml* o f h o t 95 p e rc e n t alcohol*
A fte r th e sto ra g e alcohol had been
removed by f i l t r a t i o n th e samples were washed w ith alcohol and e th e r ,
d r ie d a t 60°C* i n a vacuum oven, and ground to pass a 60 mesh s ie v e .
The t o t a l p e c tic m a te ria ls were determ ined by th e Carre-Haynes method
(9) w ith some m o d ific atio n s as d escrib ed below*
A 2 g . sample o f the
d r ie d m a te ria l was p laced in a 500 m l. Erlenmeyer f la s k , covered w ith
100 m l. o f 0*5 p e rc e n t ammonium c i t r a t e s o lu tio n , and b o ile d very gen­
t l y f o r 50 minutes*
m e tric f l a s k .
The s o lu tio n s were f i l t e r e d in to a 500 ml. volu­
The pulp was washed w ith warm w a te r, retu rn e d to th e
Erlenm eyer f la s k w ith 100 m l. of N/So h y drochloric a c id , and re flu x e d
g e n tly f o r one hour.
warm w a te r.
The m a te ria l was again f i l t e r e d and washed w ith
The f i l t r a t e s were combined, made to volume, and th e p e c tic
m a te ria ls p r e c ip ita te d from an a liq u o t as calcium p e c ta te as d escrib ed
by Carre-Haynes ( 9 ) .
The calcium p e c ta te gels were found to co n tain
im p u ritie s which according to v arious p ro te in t e s t s and n itro g e n con­
t e n t were la r g e ly p ro te in a c e o u s.
Attempts were made to estim ate th e
im p u ritie s , as d escrib ed by Appleman and Conrad ( 5 ) , by re d is s o lv in g
th e p r e c i p i ta te in ammonium c i t r a t e s o lu tio n and determ ining the un­
d iss o lv e d re s id u e .
The lim ite d q u a n tity of th e calcium p e c ta te p re ­
c i p i t a t e p re s e n t and th e extreme d i f f i c u l t y encountered i n washing
th e u n d isso lv ed im p u ritie s from th e f i l t e r paper w ith a sm all volume
o f w ater made t h i s method u n u sab le.
The im p u ritie s were estim ated by
12
d eterm in in g th e n itro g e n co n ten t o f a p o rtio n o f th e d rie d p r e c ip ita te
by th e m icro—K jeld ah l method and by c a lc u la tin g th e p ro te in content by
u se o f th e u s u a l conversion f a c t o r , 6*25*
This value was s u b tra c te d from
th e w eight o f th e o r ig in a l p r e c ip i ta te to give th e amount o f calcium
p e c ta te .
S oluble P e c tin # Four grams of the washed and d rie d p la n t sample were
t r a n s f e r r e d to a one l i t e r b o t t l e w ith 500 ml# of 0*2 p ercen t ammonium
c i t r a t e s o lu tio n .
A fte r shaking f o r one hour on a m echanical shaker th e
s o lu tio n was f i l t e r e d and a 200 ml# a liq u o t taken f o r th e determ ination
o f th e s o lu b le p e c tic m a te r ia ls , which were determ ined as describ ed f o r
t o t a l p e c tin .
P ro to o e c tin .
The percentage o f p ro to p e c tin was c a lc u la te d by sub­
tr a c t in g th e percen tag e o f s o lu b le p e c tin from th e percentage o f t o t a l
p ectin #
T o tal N itro g en .
Two p o rtio n s o f th e pulp of approxim ately 5 grams
each were p laced on ta r e d watch g la s s e s , clamped to g e th e r, weighed, th en
tr a n s f e r r e d to 800 m l. K jeld ah l f la s k s .
th e u s u a l K jeld ah l method.
The n itro g e n was determ ined by
Since no n i t r a t e s could be d e te c te d th e modi­
f i c a t i o n to in clu d e n i t r a t e s was o m itted .
E x tra c tio n o f N on-Protein N itro g en .
A sample o f 100 g . of th e
f r e s h l y ground pu lp was p laced in a m ortar and a sm all q u a n tity o f acid
washed q u a rtz sand added.
The pulp was thoroughly t r i t u r a t e d and a f t e r
th e g rad u al a d d itio n of 200 m l. o f w ater th e m ixture was tr a n s f e r r e d
onto a square o f Euck tow eling suspended over a 2 l i t e r beaker and the
e x tr a c t expressed by hand.
The re sid u e was retu rn ed to th e m ortar and
th e e x tr a c tio n re p e a te d two a d d itio n a l tim e s.
fuged to remove as much s ta r c h as p o s s ib le .
The e x tr a c t was c e n tr i­
I t was heated to b o ilin g ,
13
a few ml* o f 5 p e rc e n t FegQ3 s o lu tio n were added, and th e b o ilin g continued
f o r approxim ately 2 m in u tes.
co n ta in in g an asb esto s m at.
w ith h o t w a te r.
The s o lu tio n was f i l t e r e d in a Buchner fu n n e l
The beaker and th e mat were thoroughly washed
The f i l t r a t e was made to a volume o f 1000 m l. and p reserved
w ith to lu en e when n o t analyzed im m ediately.
T o tal N on-Protein N itro g en .
D uplicate 100 m l. a liq u o ts o f th e non­
p r o te in f i l t r a t e were analyzed as describ ed f o r t o t a l n itro g e n .
T o ta l Alpha-Amino N itro g en * A s p e c ia l p re lim in a ry procedure as p e r­
fe c te d by S tu a r t and Appleman (39) was adopted to e lim in a te e r ro r s th a t
occur i n th e u s u a l Van Slyke procedure.
A 200 m l. a liq u o t o f th e so lu b le
n o n -p ro te in e x tr a c t was p laced in a C laisen f la s k , immersed i n a w ater
b a th , a s l i g h t excess o f calcium oxide and 50 ml. o f alco h o l were added
and th e s o lu tio n d i s t i l l e d f o r one hour under a reduced p re ssu re a t a
tem perature o f 40 to 50°C.
The calcium oxide resid u e was f i l t e r e d o ff
and th e f i l t r a t e was s l i g h t l y a c id if ie d w ith a c e tic acid and made to a
volume o f 100 m l.
A liq u o ts o f 10 ml* each were used f o r th e determ ina­
tio n o f t o t a l alpha-amino n itro g e n i n th e Van Slyke a p p aratu s.
The
b u r e tte o f th e Van Slyke micro apparatus was used f o r measuring the
gas evolved.
The volume o f th e gaseous n itro g e n was reduced to stan d ­
ard co n d itio n s and th e p ro p er c o rre c tio n s made f o r the blank determ ina­
tio n s .
Basic N itro g e n .
D up licate 100 m l. a liq u o ts o f th e n o n -p ro tein ex­
t r a c t were a c id if ie d w ith 2 .5 m l. o f co n centrated s u lf u r ic a c id .
When
cooled to room tem p eratu re, 30 m l. o f phosphotungstic acid s o lu tio n
(20 g . phosphotungstic ac id and 5 g . of s u lf u r ic acid made to 100 ml.
o f s o lu tio n ) were added.
A fte r stan d in g f o r 24 hours in a r e f r ig e r a to r ,
th e s o lu tio n s were f i l t e r e d and th e p r e c ip ita te s washed thoroughly w ith
a d i l u t e s o lu tio n o f phosphotungstic a c id , co n tain in g 2.5 g . o f phospho-
14
tu n g s tic a c id and 5 g. o f s u lf u r ic ac id p e r 100 m l. o f s o lu tio n .
The
f i l t e r paper and th e p r e c ip ita te s were tr a n s f e r r e d to a K jeld ah l f la s k
and d ig e ste d as f o r t o t a l n itro g e n .
The ammonia was d i s t i l l e d in to .01
N a c id and th e excess a c id t i t r a t e d w ith .01 N base.
Mono-Amino N itro g e n .
The f i l t r a t e s from th e d u p lic a te b asic n itro g e n
samples were combined and n e u tra liz e d w ith co n cen trated sodium hydroxide.
The s o lu tio n was th en su b je c te d to th e d i s t i l l a t i o n tre atm e n t as f o r t o t a l
alpha-am ino n itro g e n . The volume o f th e approxim ately 400 ml. was reduced
to about 100 m l.
A liq u o ts o f 10 m l. each o f the s o lu tio n were used f o r
th e d eterm in atio n o f th e amino n itro g e n .
Ammonia N itro g en .
The d eterm in atio n o f ammonia was made by the a e ra tio n
method o f S essions and Shive (3 7 ).
To each o f th e 50 m l. d u p lic a te a l i ­
quots o f th e n o n -p ro te in s o lu tio n 50 m l. of th e carbonate reag en t were
added and th e samples a e ra te d f o r 12 h o u rs.
P relim in ary experim ents
showed approxim ately 99 p e rc e n t recovery of th e n itro g e n from an ammo­
nium s u lf a t e s o lu tio n co n ta in in g .2 mg. o f n itro g e n p e r m l. when tr e a te d
in a s im ila r manner.
The ammonia was c o lle c te d i n .01 N acid and th e
excess ac id t i t r a t e d w ith .01 N b ase.
Blanks were run w ith each d e te r­
m in atio n .
Amide N itro g e n .
D u p licate 50 m l. a liq u o ts of th e n o n -p ro te in ex­
t r a c t were hydrolyzed under r e f lu x condensers w ith 3 m l. o f concen­
t r a t e d s u lf u r ic a c id in a b o ilin g w ater bath f o r 2*5 hours*
The so lu ­
tio n s were f i l t e r e d , th e resid u e washed w ith a few m i l l i l i t e r s o f d ilu te
s u lf u r ic a c id , and th e f i l t r a t e n e u tr a liz e d w ith sodium hydroxide.
ammonia was determ ined by th e S essions and Shive method.
The
An attem pt
was made to determ ine th e glutam ine n itro g e n p re se n t according to the
h y d ro ly zin g c o n d itio n s d escrib ed by V ickery e t a l . (4 5 ).
A b u ffe r con­
15
s i s t i n g o f a m ixture of #1 M potassium dihydrogen phosphate and .05 M
borax “was added to 50 m l. o f th e n o n -p ro tein e x tr a c t i n o rd e r to have
th e s o lu tio n a t a pH between 6 and 7 .
The s o lu tio n s were hydrolyzed
f o r 2*5 hours i n a b o ilin g w ater b ath th en a e ra te d as f o r th e ammonia
d e te rm in a tio n .
The maximum change du rin g h y d ro ly sis was .5 pH u n i t .
Humin N itro g en .
The re sid u e s f i l t e r e d o f f follow ing th e amide
h y d ro ly s is were p lac ed i n a K jeld ah l f la s k and d ig e ste d as f o r t o t a l
n itro g e n and th e ammonia d i s t i l l a t i o n was c a r rie d out as f o r th e b a s ic
n itro g e n .
R esid u al Nitrogen*
The r e s id u a l n itro g e n was deteraiined by f in d ­
in g th e d iffe re n c e between th e t o t a l n o n -p ro tein n itro g e n and th e sum
o f th e determ ined so lu b le n itro g e n f r a c tio n s .
In th e d a ta f o r 1958
th e r e s id u a l n itro g e n re p re s e n ts th e d iffe re n c e between th e t o t a l nonp r o te in n itro g e n and th e sum o f th e t o t a l alpha-am ino, amide, and am­
monia n itro g e n .
F or 1959 i t re p re s e n ts th e d iffe re n c e between the
t o t a l n o n -p ro te in n itro g e n and th e sum o f the mono-amino, amide, b a s ic ,
ammonia, and humin n itro g e n .
MATERIAI5 AND EXPERIMENTAL PROCEDURE
The sw eet p o ta to e s used were o f th e Maryland Golden v a r ie ty ,
developed from th e
M aryland.
Y e llo w
J e rse y group, grown n ear College P ark,
In 1938 th e p o ta to e s were dug on October 11, allowed to
d ry f o r an hour o r more in th e su n sh in e, and brought to th e la b o ra ­
to r y .
The fo llo w in g day th ey were s o rte d in to lo t s co n tain in g s i x
p o ta to e s o f as n e a rly th e same s iz e and shape as p o s s ib le .
The loose
sand and s o i l p a r t i c l e s were removed by brushing l i g h t l y w ith a s o f t
b ru sh .
The l o t s w eighing 1310 ± 25 g. were divided in to two s e t s .
One s e t was p la ce d in a c u rin g oven a t a tem perature of 30 °C.
The
16
o th e r l o t s -were cured a t a tem perature o f 35°C.
The tem p eratu re, -with a
maximum -v ariatio n o f 1 1®, was re g u la te d by use o f a mercury r e la y thermor e g u la to r .
The a i r was k ep t i n co n sta n t c ir c u la tio n by a siro c c o fan lo ­
c a te d a t one end o f th e oven.
Small v en ts allow ed an exchange o f a i r and
p rev en ted an accum ulation o f carbon dio x id e in th e chamber.
The p o tato es
were k e p t i n th e cu rin g chambers f o r te n days, th en removed and s to re d i n
r e f r i g e r a to r s a t a tem p eratu re o f 9 to 10 °C.
By p la c in g th e l o t s in in ­
d iv id u a l w ire b a s k e ts , 4 x 6 x 12 in c h e s, im m ediately a f t e r s o r tin g , th e
n e ce ssa ry h an d lin g and t r a n s f e r from ovens to th e storage chambers could
be made w ith a minimum d istu rb a n c e to the r o o ts .
In 1939 th e same v a r i e t y was secured on October 5 from th e E a stern
Shore o f M aryland.
I n both y e a r s , 1938 and 1939, th e w r ite r g ath ered
th e p o ta to e s in th e f i e l d and th u s prevented b ru is e s e t c . th a t might
have been i n f l i c t e d by c a r e le s s commercial h an d lin g .
The sw eet p o ta to e s
were s o rte d in to l o t s o f s i x ro o ts each w ith an average w eight p e r l o t
o f 1700 i 25 g .
In 1939 th e l o t s were d iv id ed in to fo u r s e t s .
Each
s e t was su b je c te d to a d i f f e r e n t cu rin g co n d itio n o f tem perature and
hum idity as in d ic a te d i n th e t a b l e s .
A fte r a curing p e rio d o f 11 days
a l l l o t s were s to re d i n a r e f r ig e r a to r a t a tem perature o f 10 to 12 °C.
Analyses were made a t in te r v a ls du rin g th e curing and sto ra g e p e rio d .
EXPERIMENTAL RESULTS
Im m ediately a f t e r th e sw eet p o ta to e s had been brought from th e
f i e l d and s o rte d , one l o t was prepared f o r a n a ly s is .
termed th e h a rv e s t sample.
This l o t was
The w eights o f a l l l o t s were recorded
a f t e r th e p o ta to e s had been s o rte d and again as th e y were brought
o u t o f sto ra g e f o r a n a ly s is .
Table 1 and 2 show th e lo s s in w eight
and th e corresponding m oisture co n ten ts during th e s to ra g e p erio d o f
17
th e d i f f e r e n t l y cu red l o t s .
Table 1 .
Curing
Temperature
30° C.
Loss i n -weight and change i n percentage o f m oisture in
s-weet p o ta to e s cured a t d i f f e r e n t tem peratures and s to re d
a t 9—10°C. Curing p e rio d O ctober 12 to O ctober ZZ .
(1938 crop)
Date o f
A n alysis
Loss in
Weierht
P ercen t
M oisture
P ercent
O ct. 12
—
75.07
O ct. ZZ
6.5 4
74.99
Nov. 23
11.11
74.27
Dec. 51
18.02
73.75
Feb. 10
38*25
73.45
O ct. 12
-----
75.07
O ct. 22
8.58
74.51
Dec. 31
20.54
75.41
Feb. 10
25.29
73.10
35°C.
As -was p o in ted o u t by H asselbring and Hawkins (19) th e re i s a con
s id e ra b le lo s s i n t o t a l -weight o f th e s-weet p o ta to e s during s to ra g e , -with­
o u t any s ig n if ic a n t change i n th e m oisture c o n te n t.
18
Table 2 .
lo s s i n w eight and change i n percentage of m oisture in sweet
p o ta to e s cured under d i f f e r e n t co n d itio n s of tem perature and
hum idity and s to r e d a t 10-12°C. Curing p e rio d October 7 to
O ctober 18.
(19S9 crop)
80—85
p e rc e n t
30° c.
70—75
p e rc e n t
40° C.
P ercen t
M oisture
P ercen t
----
75.57
O ct. 13
4.67
r
74.80
O ct. 18
5.58
74.61
Nov. 24
6.96
:
«
s
Ja n .
95—100
p e rc e n t
7
S
O ct.
Loss in
1
Date of
A nalysis
•H
Curing- c o n d itio n s
Tem perature
Humidity
76.17
1
11.49
74.62
F eb. 22
11.83
75.51
O ct. 18
.76
76.81
Nov. 24
4.86
75.41
F eb. 22
6.35
76.10
O ct.
—
75.57
O ct. 13
7.51
73.84
O ct. 18
10.39
75.07
Nov. 24
16.10
74.72
Jan .
16.92
7
1
74.24
s
90—95
p e rc e n t
Feb. 22
22.68
73.47
O ct. 18
8.73
75.35
Nov. 24
13.30
Feb. 22
26.15
»
i
•»
74.42
75.00
19
C arbohydrate Transform ations in Sweet P otatoes
During Curing and Storage
The d a ta showing some o f th e carbohydrate changes th a t take p lace
d u rin g c u rin g and s to ra g e o f sweet p o tato es a re given i n Table 3.
Table 3*
Date o f
A nalysis
C arbohydrates c a lc u la te d as d ex tro se and expressed as
p ercen tag es o f th e f re s h w eight a t the time of th e
a n a ly s is . P o tato es cured from October 12 to October
ZZ and s to re d a t 9-10°C.
(1938 crop)
Curing Temperature 50 °C.
S ta rc h &
Hemicel- T otal Reducing 3
T o tal Car­
D ex trin D ex trin
S tarch
lu lo s e
Suarars Suerars t Sucrose bohydrates
P ercen t P ercen t
P ercent P ercen t P ercen t P ercent P ercen t P ercen t
O ct. 12
17.24
.2 4
17.00
.81
3.55
.64
2.91
21.60
O ct. 22
13.16
.16
13.00
.81
5.01
.49
4.52
18.98
Nov. 23
U .3 0
.18
11.62
.57
5.43
.45
4.98
17.80
8.08
20.29
: 11.13
20.90
9
Dec. 51
10.20
9.36
.84
9.46
.63
1.38
I
Feb. 10
8.02 :
7.07
.95
.66
12. 22
1.09
9
9
Curing Temperature 55°C.
O ct. 22
15.04
.19
14.85
.72
4*84
.91
3.93
20.60
Dec. 31
10.05
.89
9.16
.76
9.67
.92
8.75
20.48
Feb. 10
8.63
1.03
7.60
.67
10.21
.65
9.56
19.51
A ra p id h y d ro ly sis o f s ta r c h w ith a corresponding in c re a se in t o t a l sugars
o ccu rred d u rin g th e cu rin g process*
decreased s l i g h t l y .
D extrin and h em icellulose f r a c tio n s
The reducing sugars remained f a i r l y co n sta n t showing
o n ly a s l i g h t in c re a se in th e l o t s cured a t 30 °C. and a s lig h t in c re a se in
th e l o t s cured a t 35°C.
Follow ing c u rin g th e h y d ro ly sis o f s ta rc h continued a t a lower r a te
th ro ughout th e rem ainder o f th e sto ra g e p e rio d .
With th e changes in s ta rc h
20
c o n te n t th e re was a c lo s e ly corresponding in v e rse change in th e percentage
o f s u c ro s e .
The reducing su g a r co n te n t changed com paratively very l i t t l e .
There was a tendency f o r i t to in c re a se in th e l o t s cured a t 30 °C. and to
d e crea se i n th e l o t s cu red a t 35°C.
An in c re a se in d e x trin co n ten t oc­
c u rre d l a t e in th e season b u t th e h em icellu lo ses decreased throughout th e
sto ra g e p e r io d .
Both o f th e s e l a s t two f r a c tio n s were p re se n t in r e la tiv e ly
sm all amounts.
Table 4 .
Date of
A nalysis
Carbohydrates c a lc u la te d a s dextrose and expressed as
p ercen tag es o f th e fre s h w eight a t h a rv e st tim e. Pota­
to e s cured from October 12 to October 22 and s to re d
a t 9 to 10°C.
(1958 crop)
Curing Temperature 50°C.
S ta rc h &
Hemicel- T otal sReducing
D ex trin
D ex trin S tarc h
Sugars? Sugars
lu lo s e
P erc en t P erce n t P ercen t P ercen t Percent? P ercen t
T o tal Car­
Sucrose bohydrates
P ercen t P ercen t
•
O ct. 12
17.24
.24
17.00
.81
3.55 ?
.64
2.91
21.60
♦
O ct. 22
12.29
.15
12.14
.76
4.68 ?
.46
4.22
17.73
Nov. 23
10.48
.16
10.32
.51
4.82 :
.40
4.42
15.81
Dec. 31
8.39
.69
7.70
.52
7.78 ? 1.13
6.65
16.69
F eb. 10
4.94
.59
4.35
.41
7.53 ?
.67
6.86
12.88
Curing Temperature 55°C.
O ct. 22
13.76
.17
13.58
.66
4.43
.33
3.60
18.85
Dec. 51
8.00
.71
7.29
.61
7.70
.73
6.97
16.31
Feb. 10
6.10
.73
5.38
.47
7.22
• 46
6.76
13.79
A ll o f th e above f a c t s a re brought out more v iv id ly when th e d a ta in
Table 3 a re r e c a lc u la te d on th e b a s is of th e f re s h w eight a t h a rv e st tim e.
The r e s u l t s are given in Table 4.
21
On th e b a s is o f th e f re s h -weight a t th e tim e of a n a ly s is th e t o t a l
determ ined carbohydrates show v ery l i t t l e change du rin g th e e n tir e sto ra g e
p e rio d b u t when expressed as p ercen tag es of th e f re s h w eight a t h a rv e st
tim e a c o n sid e ra b le decrease o ccu rs.
Thus th e d a ta as p re se n te d i n Table
4 re p re s e n ts a t i u e r p ic tu r e of th e carbohydrate changes du rin g cu rin g and
storage*
H asselb rin g and Hawkins (19) showed th a t th e t o t a l determ ined
carbohydrates remained p r a c t i c a l l y co n sta n t throughout th e sto ra g e p erio d
when ex p ressed as p ercen tag es of th e w eight a t th e tim e o f analysis*
They
c a lc u la te d th e p ercen tag es on th e b a sis o f th e m oisture co n ten t i n th e
h a rv e st sample b u t n e g le c te d th e lo s s in w eight t h a t occurred during s to r ­
age.
The same r e la tio n s h ip s between th e v a rio u s f ra c tio n s are apparent
when th e d a ta are c a lc u la te d on th e b a s is o f th e d ry w eig h ts, as shown in
Tables 5 and 6*
Since th e maximum v a r ia tio n in th e m oisture content i s
l e s s th an 2 p e rc e n t i t i s to be expected t h a t th e d ry w eight b a s is would
re v e a l th e same trends*
The d iffe re n c e s in th e carbohydrate changes of th e l o t s cured a t the
two d i f f e r e n t tem peratures are v ery small*
The only n o tic e a b le v a r ia tio n
i s in th e reducing sugars as p o in te d out above.
zz
Table 5*
Date o f
A nalysis
C arbohydrates c a lc u la te d as d ex tro se and expressed as percentages
o f th e d ry w eight a t th e tim e o f an aly sis# P o tato es cured from
O ctober 12 to October 22 and s to re d a t 9 to 10°C*
(1938 crop)
Curing Temperature 30°C#
S ta rc h &
Hemicel­ T otal :Reducing
D ex trin
D extrin S tarch
lu lo s e
Sugars : Sugars
P erc en t
P erc en t P ercen t P ercen t P ercen t: P ercen t
T o tal Car­
Sucrose bohydrates
P ercen t P ercen t
♦
Oct# 12
69.16
.94
68.22
3.25
14.25:
2.57
11.68
86.66
1.95
18.10
75.90
1.76
19.36
69.19
5.26
30.70
77.19
4.10
41.92
78.72
•
Oct# 22
52.60
.64
51.96
3.25
20.05:
•
Nov# 23
45.87
#69
45.18
2.20
21.12:
•
Dec. 31
58.84
3.20
35.64
2.39
35.96:
•
Feb. 10
30.20
3.57
26.63
2.50
46.02:
Curing Temperature 55°C#
O ct. 22
59.01
.7 4
58.37
2.84
18.98
3.56
15.42
80.83
Dec. 31
57.79
3.3 4
34.45
2.85
36.35
3.50
32.35
76.99
Feb. 10
32.09
3.82
28.27
2.49
37.95
2.42
35.53
72.53
Table 6 .
Date o f
A nalysis
Carbohydrates c a lc u la te d as d ex tro se and expressed as p ercen tag es !
o f th e d ry w eight a t h a rv e st tim e. P o tato es cured from October
12 to O ctober 22 and s to re d a t 9 to 10 °C.
J
(1938 crop)
'
Curing Temperature 50°C.
Hemicel- T o tal Reducing
S ta rc h &
S
ta
rc
h
lu lo s e
D
ex
trin
Sugars Sugars
D extrin
P
ercen
t
P
ercen
t
P
ercen
t
P erc e n t P ercen t
P ercen t
: T o ta l Car-s
S ucrose: bohvdrafces
P e rc e n t: P ercen t
O ct. 12
69.16
.94
68.22
3.25
14.25
2.57
11.68
86.66
O ct. 22
49.14
♦60
48.54
3.0 4
18.73
1.82
16.91
70.91
Nov. 23
40.67
.61
40.05
1.95
18.72
1 .5 4
17.16
61.34
Dec. 31
31.84
2.63
29.22
1.96
29.48
4.31
25.17
63.28
Feb. 10
18.64
2.20
16.44
1.5 4
28.41
2.53
25.88
48.59
Curing Temperature 55eC.
:
2.59
17.35
.68
: 53.34
3.25
14.10
73.86
O ct. 22
53.92
Dec. 31
30.03
2.66
:
27.37
2.27
28.88
2.78
26.10
61.18
Feb. 10
25.50
3.04
:
22.46
1.97
30.15
1.92
28.23
57.62
23
P e c tic Changes In Sweet P o tato es During Curing and S torage
Since firm n ess and keeping q u a lity o f many f r u i t s and v eg etab les seem
to be c lo s e ly c o r re la te d w ith th e changes th a t occur in th e p e c tic m a te ria l
i n th e t i s s u e s , i t was co n sid ered d e s ira b le to determ ine some o f th e p e c tic
c o n s titu e n ts i n th e sweet p o ta to e s during cu rin g and s to ra g e .
Tables 7 and
8 give th e r e s u l t s f o r th e 1938 crop.
The d a ta i n Table 7 in d ic a te t h a t th e t o t a l p e c tic m a te ria l was higher
i n a l l o f th e s to r e d l o t s than in th e o r ig in a l h a rv e st sam ples,
lfihen th e
d a ta are r e c a lc u la te d as p ercen tag es o f the fre s h w eight a t h a rv e st tim e an
in c re a se i n th e t o t a l p e c tic m a te ria l occurred on ly during th e cu rin g p e rio d .
A s l i g h t d ecrease o ccurred d u ring th e e a r ly p a r t of th e sto ra g e p e rio d .
The
samples analyzed on F ebruary 10 showed co n sid erab le decrease in th e t o t a l
p e c tic m a te r ia l.
These l o t s were beginning to break down and decay.
may have accounted f o r th e l o s s .
This
No decayed tis s u e s were used f o r a n a ly s is
b u t a l l o f th e p o ta to e s o f th o se l o t s co n tain in g decayed m a te ria l were much
s o f t e r th an th e p o ta to e s in th e o th e r lo ts *
Table 7 shows t h a t th e so lu b le
p e c tin and p ro to p e c tin were p re s e n t i n la r g e r q u a n titie s in n e a rly a l l o f
th e s to r e d l o t s th an in th e o r ig in a l h a rv e st sample.
24
Table 7 •
Curing
Temoerature
30 °C.
35 °C.
Table 8 .
Curing
Temoerature
30 *C.
35°C.
P e c tic c o n s titu e n ts c a lc u la te d as calcium p e c ta te and expressed
as p ercen tag es of th e f re s h w eight a t th e time o f analysis*
P o ta to e s cured a t d if f e r e n t tem peratures and s to re d a t 9—10 °C •
Curing p e rio d O ctober 12 to O ctober 22.
(1938 crop)
Date o f
A nalysis
T otal
P e c tin
P ercent
Soluble
P e c tin
P ercen t
O ct. 12
.808
.399
.409
O ct. 22
.919
.349
.570
Nov. 23
.879
.425
.454
Dec. 31
.971
.588
.383
Feb. 10
.968
.535
.433
O ct. 22
1.068
.465
*603
Dec. 31
1.052
.651
.401
Feb. 10
1.006
.555
.451
P ro to n e c tin
P ercent
P e c tic c o n s titu e n ts c a lc u la te d as calcium p e c ta te and expressed
as p ercen tag es o f th e f r e s h w eight a t h a rv e st tim e. P o tato es
cured a t d i f f e r e n t tem peratures and s to re d a t 9—10 °C.
Curing p e rio d O ctober 12 to October 22.
(1938 crop)
Date o f
A nalysis
T otal
P e c tin
P ercen t
Soluble
P e c tin
P ercen t
P ro to o e c tin
P ercen t
O ct. 12
.808
.399
.409
O ct. 22
.858
.326
.532
Nov. 23
.781
.377
.404
Dec• 31
.798
.483
.315
Feb. 10
.596
.329
.267
O ct. 22
.976
.425
.551
Dec. 31
.858
.518
.320
Feb. 10
.711
.392
.319
25
Expressed as p e rc e n t o f th e f re s h ■weight a t h a rv e st tim e th e so lu b le p e c tin
rem ained more n e a rly c o n sta n t -while p ro to p e c tin in cre a se d during th e cu rin g
p e rio d th en decreased throughout th e rem ainder of th e sto ra g e p e rio d .
The d a ta f o r th e p e c tic c o n s titu e n ts in th e 1959 crop are p resen ted in
ta b le s 9 and 10.
Here, as in th e previous y e a r, th e t o t a l p e c tic m a te ria l
in c re a se d d u rin g s to ra g e b u t c a lc u la te d on th e b a sis o f th e h a rv e st w eight
th e o n ly c o n s is te n t in c re a se in a l l cases was d u rin g cu rin g .
A r a th e r con­
s i s t e n t in c re a s e i n p ro to p e c tin occurred throughout sto rag e in th e l o t s
cured a t 50 °C.
The l o t s cured a t 40 °C. were le s s c o n s is te n t but in most
cases co n tain ed more p ro to p e c tin than th e h a rv e st sam ple. The l o t s cured
a t 40 °C. and high hum idity showed a decrease i n a l l th e p e c tic f ra c tio n s
on th e l a s t sam pling d a te .
This l o t was i n a r e l a t iv e ly poor c o n d itio n .
Some of th e ro o ts were beginning to show decay.
The sto ra g e sy n th e s is of p ro to p e c tin ap p aren tly continues in the
ro o ts u n t i l th e f i r s t in d ic a tio n o f decay i s n o tic e a b le .
This discon­
tin u an ce o f p ro to p e c tin s y n th e s is i s follow ed by a decrease in th e t o t a l
p e c tic c o n s titu e n ts and to some e x te n t a decrease in th e s o lu b le p e c tin .
26
Table 9*
P e c tic c o n s titu e n ts c a lc u la te d as calcium p e c ta te and expressed
as p ercen tag es o f th e f r e s h "weight a t tim e o f analysis* P otatoes
cured under d i f f e r e n t co n d itio n s o f tem perature and hum idity
and s to re d a t 10 to 12°C. Curing p erio d October 7 to October 18
(1939 crop)
Curing C onditions
Temoerature
Humidity
Date o f
A nalysis
O ct.
80—85
p e rc e n t
50 °C.
95—100
p e rc e n t
70—75
p e rc e n t
90—95
p e rc e n t
Soluble
P e c tin
P ercen t
P ro to n ec tin
P ercen t
7
.776
♦426
.350
O ct. 15
.837
.444
.393
O ct. 18
.927
.608
.319
s
Nov. 24
1.017
.575
.442
Jan .
1
1.059
.336
.723
Feb. 22
1.127
.385
.742
O ct. 18
.854
.542
.312
Nov. 24
1.065
.489
.576
Feb. 22
1.240
.424
.816
O ct. 13
.984
.481
O ct. 18
.977
.649
.328
Nov. 24
.995
.545
.450
1
1.025
.303
.722
Feb. 22
1.373
.391
.982
Oct* 13
.913
.471
.442
O ct. 18
.913
.655
Jan .
40 °C.
T o tal
P e c tin
P ercent
I;
.503
.258
:
Nov. 24
1.196
.557
.639
Feb. 22
1.021
.418
.603
27
Table 10.
P e c tic c o n s titu e n ts c a lc u la te d as calcium p e c ta te and expressed
as p ercen tag es of th e f r e s h "weight a t h a rv e st tim e. P o tato es
cured under d if f e r e n t co n d itio n s of tem perature and hum idity
and s to re d a t 10—12 °C. Curing p erio d October 7 to October 18.
(1939 crop)
Curing C onditions
Temoerature
Humiditv
Date of
A nalysis
O ct.
80—>85
p e rc e n t
30 °C.
95—100
p e rc e n t
Total
P e c tin
P ercent
Soluble
P e c tin
P ercen t
P ro to o ec tin
P ercent
7
.776
.426
.350
O ct. 13
.798
.423
.375
O ct. 18
.876
.574
.302
Nov. 24
.946
.635
.411
Jan.
1
.937
.298
.639
Feb. 22
.994
.339
.654
O ct. 18
.847
.538
♦309
Nov. 24
1.013
.465
.548
Feb. 22
1.089
.372
.717
O ct. 13
.910
.445
.465
.876
.582
.294
Nov. 24
.855
.458
.377
Jan .
1
.922
.252
.670
Feb. 22
1.062
.302
.759
O ct. 13
.856
.442
.414
O ct. 18
.833
.598
.235
Nov. 24
1.037
.483
.554
Feb. 22
.754
.309
.445
O ct. 18
i
70—75
p e rc e n t
40°C.
90— 95
p e rc e n t
28
E ffe c ts o f S torage in an Aqueous S o lu tio n
On th e N on-Protein N itrogen F ractio n s
W ebster (46) has shown t h a t a lc o h o lic s o lu tio n s o f p la n t m a te ria ls
show a c o n tin u a lly d ecrea sin g p ercentage of amino n itro g e n during sto rag e
re g a rd le s s o f th e c o n c e n tra tio n o f a lco h o l used.
He found an in crease in
ammonia n itro g e n which did n o t account f o r al l of th e decrease in amino
n itro g e n .
The fo llo w in g experim ent was undertaken to determ ine w hether a
s im ila r s h i f t o f th e n o n -p ro te in n itro g e n f ra c tio n s occurs during sto rag e
i n an aqueous s o lu tio n p reserv ed w ith to lu e n e .
The s o lu b le n itro g e n was e x tra c te d from d u p lic a te 100 g . samples o f
th e pulp from th e 1939 h a rv e s t l o t o f sweet p o ta to e s.
removed and th e s o lu tio n s made to volume.
m ed iately .
One s o lu tio n was analyzed im­
The o th e r s o lu tio n was covered w ith toluene and sto re d in a
dark chamber a t room tem p eratu re.
A fte r 4 months o f sto rag e th e s o lu tio n
was analyzed by th e u s u a l p rocedure.
Table 11.
The r e s u l t s are given i n Table 11.
d i s t r i b u t i o n o f n itro g e n in s to re d and u n sto red aqueous
n o n -p ro te in n itro g e n e x tr a c ts o f sweet p o ta to e s . The
r e s u l t s are expressed as percentages o f th e fre s h w eig h t.
• NonT o tal; P ro te in
N :
N
Percehb P ercen t
:Alpha : Mono-:
Ammonia:Amino : Amino: Amide: Basic R esidual
N
N 2 N
; _.N_ _*_ N :
N
P e rc e n t; P ercenfe P er certs Pe rcenb Per cert P ercen t
•
•
.0003 ;.0286 ; .0193: .0015: .0075
.0122
•
•
•
H arvest
Sample
A fte r 4
months
sto ra g e
The p ro te in s were
P ro te in
N
P ercen t
•
*1899 ;
.1899 :
.0408
.0407
.1491
.1492
•
•
•
•
*
•
•
•
•
.0005 s.0201 ; .0143: .0021: .0061
.0177
Although no marked changes were n o ted , th e re was a decrease i n amino
n itro g e n and a s l i g h t in c re a se in ammonia and amide n itro g e n .
The in c re a se
i n th e l a s t two f r a c tio n s does n o t account f o r a l l o f th e decrease in the
amino n itro g e n , thus th e g r e a te s t in c re a se occurred in th e r e s id u a l f r a c tio n .
29
U nless s ta t e d o th e rw ise , the d a ta in th e follow ing ta b le s re p re se n t th e
r e s u l t s o f f r a c tio n a tio n im m ediately a f t e r e x tr a c tio n .
N itrogen Metabolism in Sweet P o tato es
During Curing and Storage
I n Tables 1 and Z i t was shown th a t th e re i s a con sid erab le lo s s in t o t a l
w eight o f sw eet p o ta to e s d u rin g cu rin g and s to ra g e .
In o rd er to take in to
account t h i s lo s s o f w ater and d ry m a tte r, th e r e s u lt s f o r a ll n itro g e n d e te r­
m in atio n s, a f t e r having f i r s t been p resen ted as percentages o f th e f re s h
w eight a t th e tim e o f a n a ly s is , a re given in subsequent ta b le s from rec a lc u ­
la te d d a ta as p ercen tag es o f th e f r e s h w eight a t h a rv e st tim e.
f o r th e 19S8 experim ents a re given in ta b le s 12 and IS .
The r e s u lts
The 1939 r e s u lts
are g iv en i n ta b le s 14, 15, 16 and 17.
During th e c u rin g p ro ce ss a co n sid e rab le h y d ro ly sis of p r o te in occurred.
The r a t e o f h y d ro ly sis was g r e a te r i n a l l cases a t th e h ig h e r tem peratures
and also f o r th e h ig h e r h u m id ities a t th e same tem p eratu re.
Concomitant w ith
th e in c re a se i n th e t o t a l so lu b le n o n -p ro tein n itro g e n th e re was an in c re a se
i n n e a rly a l l o f th e s o lu b le f r a c ti o n s .
Amino and b a sic n itro g e n in creased
more ra p id ly a t th e h ig h e r cu rin g tem p eratu res.
th e fo rm ation o f b a s ic n itro g e n .
High hum idity tended to fav o r
Amide n itro g e n was somewhat v a ria b le and
showed d ecreases d u rin g cu rin g in th e 1938 experim ents and in c re a se s i n
1939.
The h u m id ities were n o t determ ined in th e 1938 experim ents b u t probably
corresponded c lo s e ly to th o se o f th e lower hum idity s e ts i n th e 1939 ex­
p erim e n ts.
50
Table 12*
D is trib u tio n of n itro g e n expressed as percentages o f the
f re s h w eight a t th e tim e of a n a ly s is . Cured from October
12 to October 22 and s to re d a t 9 to 10 °C.
(1938 crop)
Curing Temperature 50 °C.
NonAlpha :
Date o f
T o ta l P ro te in P ro te in Ammonia Amino
Amide
Basic
A nalysis
N
N
N
N
N
N
. N___
P ercen t P ercen t P ercen t P ercent P e rc e n t: Perc en t Percent
•‘- v
R esidual
N
P ercent
4
O ct. 12
.217
.145
.072
.0010
.047
.008
.010
.016
O ct. 22
.259
.149
.090
.0016
.047
.006
.015
.055
Nov. 25
.264
.166
.098
.0013
.052
.010
.022
.055
Dec. 51
• 256
.160
.096
.0020
.029
.018
.021
.047
Feb* 10
.245
.135
.108
.0015
.012
.019
.018
.075
Curing Temperature 55°C.
O ct. 22
.273
.163
.110
.0014
.067
.002
.024
♦040
Dec. 31
.260
.142
.118
.0025
.032
.020
.022
.063
Feb. 10
.319
.158
.161
.0022
.017
.055
.030
.109
Table 15*
D is tr ib u tio n of n itro g e n expressed as percentages of th e
f r e s h w eight a t h a rv e st tim e. P o tato es cured from. October
12 to O ctober 22 and s to re d a t 9 to 10 °C.
(1958 crop)
Curing Temperature 50°C.
Alpha
NonAmide
Basic
T o tal P ro te in P ro te in Ammonia Amino
Date o f
N
N
N
N
N
N
A nalysis
N
P ercen t P ercen t P ercen t P ercen t P ercen t P ercent P ercen t
R esidual
N
P ercen t
O ct. 12
.217
♦145
.072
.0010
.047
.008
.010
.016
O ct. 22
.223
.139*
.084
.0015
.044
.006
.014
.032
Nov. 23
.235
.ih
.087
.0012
.028
.009
.020
.049
Dec. 31
.210
.1 3 1
.079
.0016
.024
.015
.017
.038
Feb.. 10
flflCL
.083 _? .066_
.*007 __ *012.
-OIL
.. -046,
.002
.022
.036
.016
.017
.051
.025
.022
O ct. 22
.250
.150
Dec. 31
.207
.113
«^QDSL-
Curing Temperature 55°C*
•
s
♦100 • .0013 s .061
.094
•
4
5 .0020
* .025
.238
.118
.120
s .0016
j
.013
o
Feb. 10
.
o
00
9
Table 14,
D istrib u tio n of n itrogen expressed as percentages of the fre s h weight a t th e time o f
a n a ly sis. Potatoes cured a t d if fe re n t tem peratures and hum idities and sto re d a t 10
to 12°C. Curing period October 7 to October 18.
(1939 crop)
Curing tem perature 50 °C.. r e la tiv e hum idity 80 to 85 p e rc e n t
i NonAlpha
Mono
t
P ro te in : P ro te in
T o tal
Amino
•Ammonia Amino
Humin
Amide s Basic
N
N
:
N
N
i
N
N
N.
_JJ
N ......
P e rcen t P ercen t
P erc e n t
P ercent P ercent P ercen t P e rc e n t:P ercen t P ercen t
-
Date o f
A nalvsis
■
M oisture
P ercen t
. . .
..
.
.
i
Oct.
7
75.57
.190
.149
R esidual
N
P ercen t
*
.041
.0003
.029
.019
.0015 J .008
♦0000
.012
.0005
.012
«
O ct. 13
74.80
.196
.150
.046
.0006
.043
.022
Oct. 18
74.61
.172
.123
.049
.0004
.026
.018
Nov. 24
76.17
.169
.110
.059
.0007
.032
Jan.
1
74.62
.164
•H I
.053
.0006
Feb. 22
75.51
.201
•
113
.088
.0002
.0003
.019
.023
.0022 t .009
t
.0035 : .008
s
.0031 : .015
.0017
.016
.029
.022
.0026 i .018
.0009
.009
.049
.033
.0071 s .018
.0004
. *029
________
Curing tem perature 50CC«. r e la tiv e hum idity 95 to 100 p ercen t
O ct. 18
76.81
.190
.133
.057
:
.0003
.030
.020
.0036
.013
.0006
.020
Nov. 24
75.41
.193
.133
.060
:
.0006
.036
.031
.0042
.012
.0014
.011
Feb. 22
76.10
.185
.129
.056
i
I
.0002
.030
.023
.0030
.027
.0000
.003
03
H
Table 15.
Curing tem perature 40°C .. r e l a tiv e hum idity 70 to 75 p e rc e n t
i
Non: Alpha Mono
P ro te in
Ammonia : Amino
P ro te in
Amino Amide : Basic : Humin : R esidual
T o ta l
:
N
N
N
!
N
N
-N
. : . N . .N .
N. ....
. .N
P ercen t
P ercent :P ercen t: P ercen t P ercent{P ercent P ercen ts P ercen t
Percent^ P ercen t
9
9
4
4
Date o f
A nalvsis
D istrib u tio n of nitrogen expressed as percentages of th e fre s h w eight a t th e time of
analysis* Potatoes cured a t d iffe re n t tem peratures and hum idities and sto re d a t 10
to 12*C. Curing period October 7 to October 18. (1959 crop)
M oisture
Percent
.
i
i
7
75,57
.190
.149
.041
.0005
.029
.019
.0015
.008
.0000 :
.012
O ct. 15
75.84
.172
.105
.069
.0006
.055
.059
.0053
.009
.0015
.014
Oct. 18
75.07
,195
.098
.097
.0006
.065
.050
.0096
.014
.0016
.021
Nov. 24
74.72
,220
.150
.090
.0024
.048
.034
.0140
.018
.0016
.020
Jan.
1
74.24
.212
.107
.105
.0015
.058
.050
.0086
.027
.0026
.016
Feb. 22
75.47
.250
.107
.125
. *QQ2£
. .063
.046
.0178
.0027
.029
75.55
Curing
tem perature 40 °C .. r e la tiv e hum idity 90 to 95 percen t
U
UJL.
••
%
%
.060
.093
.0004
.047 : .0092 S .014
.061
.154
.0020
.020
.0005
.020
.0027
.029
Oct.
O ct. 18
Nov. 24
74.42
.189
.105
.084
.0014
.047
.037
Feb. 22
75.00
.230
.091
.139
.0015
.069
.056
:
i
j .0103 ! .015
:
:
i .0227 s .027
♦
9
**
03
ro
Table 16.
D istrib u tio n o f n itro g en expressed as percentages of the fre s h weight a t h arv est
tim e. Potatoes cured a t d if fe re n t tem peratures and hum idities and sto re d a t 10
to 12°C. Curing period October 7 to October 18.
(1959 crop)
Curing tem perature 50°C .. r e la t iv e hum idity 80 to 85 p e rc e n t
*
«
NonAlpha Mono- ••
«
I
P ro te in
T o tal
P ro te in
Ammonia Amino
Amino : Amide : Basic i Humin
R esidual
N
N
N
N
:
N
. . _BL r _. N___ :
N
:
N
P ercen t P e rc en t
P ercen t
P ercen t P ercen t P ercen t P ercen t sP ercen t i P ercent P ercen t
9
Date o f
A nalvsis
»
7
.190
.149
.041
.0003
.029
.019
.0015 t
O ct. 15
.187
.145
.044
.0006
.041
.021
.0021
Oct.
•
.008 : .0000
:
.009 i .0005
.012
.011
t
O ct. 18
.162
.116
.046
.0004
.025
.017
.0033
.008
.0003
.017
Nov. 24
.157
♦102
.055
.0007
.050
.021
.0029
.014
.0016
.015
Jan.
.145
.098
.047
.0005
.026
.019
.0023
.016
.0008
.008
.099
.078
.0002
.045
.029
.0065
.016
.0004
.026
1
«
Feb. 22
.177
Curing tem perature 50 °C.. r e la tiv e hum idity 95 to 100 p ercen t
O ct. 18
.189
.132
.057
.0003
.030
.020
.0036
.013
.0006
.020
Nov. 24
.184
.127
.057
.0006
.034
.029
.0040
.011
.0013
.011
Feb. 22
.162
.113
.049
.0002
.026
.020
.0026
.024
.0000
.002
C*J
ot
Table 17.
Date of
Analvsis
O ct.
7
D istrib u tio n of n itrogen expressed as percentages of the fre s h -weight a t h a rv e st
tim e. P otatoes cured a t d iffe re n t tem peratures and hum idities and sto red a t 10
to 12°C. Curing period October 7 to October 18.
(1939 crop)
Curing tem perature 40°C». r e l a tiv e hum idity 70 to 75 p e rc e n t
■
NonAlpha : Mono :
;
:
P ro te in
P ro te in
T otal
Ammonia Amino : Amino ; Amide : Basic : Humin
N
N
N
.
N_
N
:
N
:
N
:
N
* N
P ercen t
P ercen t P ercen t
P ercen t P ercen t :P ercen t j P ercen t sPercent sPercent
•
•
•
•
.190
•149
.041
.0003
.029 : .019 i .0015 : .008 : .0000
•
Oct. 13
.159
.095
.064
.0006
.049 :
«
.036 : .0049
•
Oct. 18
.175
.088.
.087
.0005
.058 :
.045
•
Nov. 24
.185
.109
.076
.0020
.040 :
1
.176
.089
.087
.0011
.048
i
Feb. 22
.178
.083
.095
.0012
:
:
«
:
.0086 s
«
:
.008 ; .0014
«
.013 s .0014
.019
•
.015 s .0013
.017
*
.022 i .0022
•
.036 ; .0138 :
.013
•
•
.042 s .0071 s
.012
«
•
.029 : .0117
i
.049 !
i
•
•
•
Jan.
*
R esidual
N
P ercent
.013
i
.020
:
.0021
.022
Curing tem perature 40 °C .. r e l a tiv e hum idity 90 _y«
to 95
viv p ercen t
•
O ct. 18
.141
.056
.085
.0004
.055 :
.043
.0084
.013
.0018
.018
Nov. 24
.164
.091
.073
.0012
.041 ;
.032
.0089
—to
H
O
*
.0004
.018
Feb. 22
.170
.067
.103
.0011
.051 :
.041
.0167
.020
.0020
.022
03
55
Ammonia and humin n itro g e n in creased during cu rin g .
These forms o f
n itro g e n were p re s e n t in v ery sm all amounts and in most cases re p re se n t
l e s s th a n one p e rc e n t of th e t o t a l nitrogen*
i n every case d u rin g th e curing p e rio d .
R esidual n itro g en in creased
I t should be remembered th a t the
r e s id u a l n itro g e n in th e 1938 experim ents re p resen ts th e d iffe re n c e be­
tween the t o t a l so lu b le non—
p ro te in n itro g e n and the sum of the ammonia*
alp h a amino, and th e amide n itro g e n .
The re s id u a l n itro g e n of the 1939
d a ta re p re s e n ts th e d iffe re n c e between the t o t a l so lu b le n o n -p ro tein
n itro g e n and th e sum o f th e ammonia, mono-amino, amide, b a s ic , and humin
n itro g e n .
Although th e tre n d in the re s id u a l n itro g e n f r a c tio n was the
same d u rin g th e curing p e rio d f o r th e two years considerable v a ria tio n
occurs d u rin g storage*
This may be due in p a r t to th e method o f calcu­
la tio n .
The h y d ro ly sis o f p r o te in co ntinues to some e x te n t a f te r th e sweet
p o ta to e s a re p lac ed in s to ra g e .
An in c re a se in th e n o n -p ro tein f r a c tio n
i s noted p a r t ic u la r l y in th e February sampling o f both y e a rs.
The l o ts
cured a t 30 °C. and high hum idity showed th e l e a s t p r o te in h y d ro ly sis o r
change in th e r e l a t i v e amounts of p r o te in and so lu b le n o n -p ro tein n i tr o ­
gen during th e sto ra g e p e rio d .
Amide n itro g e n in c re a se d during th e l a t t e r p a r t of th e sto ra g e
p e rio d and to a much g r e a te r e x te n t in th e l o t s cured a t th e h ig h er
tem p eratu re.
The glutam ine n itro g e n co n ten t o f th e h a rv e st sample was approxi­
m ately .0005 p e rc e n t o f the f r e s h w eight o r one th ir d of th e amide n i t r o ­
gen.
No glutam ine n itro g e n could be d e te c te d in th e l o t s cured a t 30°C.
i n th e February sam pling.
The changes i n th e amino n itro g e n were not c o n s is te n t.
A decrease
56
occu rred during s to ra g e in th e 1958 experim ents "while in 1939 th e amino
n itro g e n tended to remain more n e a rly c o n sta n t.
A s l i g h t tren d toward
an in c re a s e may be p re se n t i n th e l o ts cured a t th e lower tem peratures*
No v e ry d e f i n it e tre n d s occur in th e ammonia and humin n itro g en
d u rin g sto ra g e ex cep t t h a t th ey appear in la r g e r q u a n titie s in th e l o ts
cured a t th e h ig h e r tem penatures.
B asic n itro g e n in c re a se d during th e storage p e iio d .
In 1938 the
f lu c tu a tio n s i n t h i s f r a c tio n were com paratively sm all but in 1939 an
in c re a s e was noted i n a l l s e t s . *
The r e s id u a l n itro g e n in cre a se d during sto ra g e i n both s e ts of ex­
perim ents in 1938.
in c r e a s e .
In 1939 th e re was only a s l i g h t tendency toward an
An ex cep tio n was noted in the l o t s cured a t 30 °C. and high
hum idity where a decided decrease in th e r e s id u a l n itro g e n occurred.
■Whether any s ig n ific a n c e can be a tta c h e d to th e m id-storage season de­
crease and th e l a t e r in c re a se in th e r e s id u a l n itro g e n in th e l o t s o f
th e o th e r th re e s e ts in th e 1939 experim ents i s n o t known.
The r e l a t iv e d i s t r ib u tio n o f the v ario u s n itro g e n fra c tio n s i s
more c l e a r l y shown by e x p ressin g them as percentages of th e t o t a l n i t r o ­
gen.
These r e s u l t s are given in Tables 18 and 19.
The changes in the
v a rio u s f r a c tio n s t h a t were p re v io u sly p o in ted o u t become more ev id en t
a f t e r a stu d y o f th e se t a b l e s .
37
Table 18*
P ro te in
N
P erc en t
NonP ro te in
P ercen t
»
Alpha a
a
Ammonia Amino i Amide t Basic
R esidual
N
N
* N a N
N
P ercen t P e rc e n t:P e rc e n t:P ercent P ercen t
9
O ct. 12
66.82
33.18
.46
21.66 a 3.69
s 4.61
7.37
O ct. 22
62.34
37.66
.67
19.67 a 2*51
a 6.28
14.81
Nov. 23
62.88
37.12
.49
12.12 a 3.79
a 8.33
20.72
Dec. 31
62.50
37*50
.
00
Date o f
A nalvsis
D is trib u tio n o f n itro g e n expressed as percentages of the
t o t a l n itro g e n in sweet p o tato es cured a t d if f e r e n t
tem peratures and sto re d a t 9 to 10 °C. Curing p erio d
O ctober 12 to October 22. (1938 crop)
11.33 a 7.03
a 8.20
18.36
Feb. 10
55.56
44.44
.62
4.94 a 7.82
a 7.4L
31.06
Curing tem perature 35°C.
O ct. 22
59.71
40.29
.51
24.54
.73
8.79
14.51
Dec. 31
54.62
45.38
.96
12.31
7.69
8.46
24.42
Feb. 10
49.53
50.47
.69
5.33
10.34
9.40
34.11
38
Table 19*
D is tr ib u tio n o f n itro g e n expressed as percentages o f th e t o t a l
n itro g e n in sweet p o tato es cured a t d if f e r e n t tem peratures and
h u m id ities and sto re d a t 10 to 12 °C. Curing p erio d October 7
to October 18*
(1939 crop)
_Curing tem peratu r e 30°C*. r e la tiv e hum idity 80 to 85 percent
NonAlpha : Mono- ;
•
Date
P ro te in P ro te in Ammonia Amino : Amino : Amide
Basic : Humin Residua
A nalvsis
N
N '
N
N
:
N :
N
N
N
s N
P ercen t P ercen t P ercen t P ercent P ercent :Percent P ercen tiP e rcen t P ercent
O ct.
•
7
78.42
21.58
.16
15.26
10.00 :
.79
4.21 :
.00
6.42
O ct. 13
76.47
23.53
.32
21.93
H .2 3 ! 1.12
4.81 |
.27
5.78
O ct. 18
71.60
28.40
.25
15.43
10.49 I 2.04
4 .9 4 1
.19
10.49
Nov. 24
64.97
35.03
. 45
19.11
13.38 | 1.85
8.92 | 1.02
9.41
Jan .
1
67.59
32.41
.34
17.93
13.10 I 1.59
11.03 !
.55
5.80
Feb. 22
55.93
44.07
.11
24.29
16.38 * 3.56
9.04 I
.23
14.75
Curing tem perature 30 °C . r e la tiv e hum iditv 95 to 100 p ercen t
Oct. 18
69.84
30.16
.16
15.87
10.58 J 1.90
6.88 J
.32
10.32
5.98 !
.71
6.03
14.81 *.
.00
1.36
•
Nov. 24
69.02
30.98
.33
18.48
15.76 ! 2.17
•
Feb. 22
69.75
30.25
16.05
.12
12.35 1 1.61
Curing tem oerature 40 °C*. r e la tiv e hum iditv 70 to 75 p e rc e n t
•
O ct. 13
59.75
40.25
.38
30.82
22.64 i 3.08
•
.88
8.2 4
.80
10.57
.70
9.19
12.50 ! 1.25
7.17
5.03 |
•
O ct. 18
50.29
49.71
.29
33.14
25.71 ! 4.91
7.43 |
•
*
Nov. 24
58.92
41.08
1.08
21.62
15.68 1 6.32
8.11 J
•
Jan.
1
50.57
49.43
27.27
.62
23.86 j 4.03
•
Feb. 22
46.63
53.37
.67
27.52
20.22 ! 7.75
11.24 I 1.18
12.36
Curing tem p eratu re 40eC*. r e la t iv e hum idity 90 to 95 p e rc e n t
Oct* 18
39.72
60.28
.28
39.01
30.50 : 5.96
9.22
1.28
Nov. 24
55.49
44.51 *
.73
25.00
19.51 ! 5.43
7.93
.24
• 13.04
:
s 10.67
F eb, 22
59.41 ; 60.59 :
.65
11.76 * 1.18
I 13.06
*
»
30.00 a 24.12 * 9.82
it
39
D is tr ib u tio n o f Nitrogenous Compounds i n the Proxim al
and D is ta l Ends of the Sweet Potato
I t has been shewn t h a t th e seed and stem ends o f th e I r i s h p o ta to
tu b e r d i f f e r i n c o n te n t and form of n itro g e n (4)*
This suggested th e
p o s s i b i l i t y of a d iffe re n c e i n th e n itro g e n d is tr ib u tio n of th e proxim al
and d i s t a l ends o f th e sweet p o ta to .
Analyses -were made o f th e proxim al and d i s t a l halves o f the h a rv e st
sample and o f p o ta to e s t h a t had been i n storage f o r wix -weeks.
samples were e x tra c te d on th e d ates in d ic a te d in th e ta b le .
The
The non­
p r o te in n itro g e n s o lu tio n was p reserved w ith to lu e n e , sto re d a t room
tem p eratu re, and analyzed on February 9.
The r e s u l ts are given in
Table 20.
Table 20.
T o ta l
N
M oisture
Proximal
h a lf
D is trib u tio n o f n itro g e n in the proxim al and d i s t a l
halves o f sweet p o ta to e s . R esu lts are expressed as
p ercen tag es o f th e fre s h w eight a t th e tim e of ana­
ly s is .
.187
75*68
H arvest sample. October 7.
NonAlpha Mono
Amino
P ro te in Ammonia Amino
N
N
. N
IL
.044
.0011
.020
.013
Amide
N
Basic
— N
.003
.010
.017
.003
i
♦
•
.010 :
.018
D is ta l
h a lf
75.60
.181
Proximal
h a lf
«•
75.84 :
P o tato es cured and s to re d u n t i l November 27.
i ^
»»
.036
.062
.0012
.178
.008
.010
.018
D is ta l
h a lf
.044
.0008
.019
.012
Residual
--N ..
.025
i
75.81
.172
.054
.0016
— *032,
.019
.007
.013
The proxim al h a lf showed a s li g h t l y h ig h e r t o t a l n itro g e n c o n te n t.
.013
The
v a r ia tio n s were so sm all t h a t i t may be concluded from t h i s experim ent th e re
i s no apparent d iffe re n c e in th e n itro g e n d is tr ib u tio n in th e proxim al and
40
d i s t a l h alv es o f th e sw eet p o ta to .
Distribution o f N itrogenous Compounds i n th e Inner
and O uter Areas o f th e Sweet P o tato
In th e m ature sweet p o ta to ro o t a somewhat ir r e g u la r b u t d i s t i n c t
cambium r in g s e p a ra te s a narrow c o rte x and periderm from th e in n e r areas
o f s to ra g e parenchyma and v a sc u la r t i s s u e .
Sweet p o ta to e s i n a h a rv e s t l o t and i n a l o t t h a t had been in sto rag e
f o r 6 weeks were d iv id ed in to in n e r and o u te r p o r tio n s .
A f a i r m echanical
se p a ra tio n o f th e two a re a s was made by u sin g a sharp k n if e .
The in n e r
p o rtio n co n tain ed th e g r e a te r p a r t o f th e m eristem atic t is s u e o f the
cambium ring*
The samples were e x tra c te d .
The s o lu b le n o n -p ro te in f r a c ­
tio n was p re se rv e d w ith to lu e n e , s to re d , and analyzed on F ebruary 10.
The r e s u l t s a re given i n ta b le 21.
Table 21.
D is tr ib u tio n o f n itro g e n in th e in n e r and o u te r p o rtio n s
o f th e sweet p o ta to expressed as p ercen tag es o f th e fre s h
w eight a t th e time o f a n a ly s is .
••
H arvest sample. O ctober 7.
Non- j
Alpha Mono
Amino
ProteiaAmmonia Amino
N
N
N
_ N ....
M oisture
T o ta l
N
Outer
p o rtio n
74.46
.178
.037
.0031
.012
Inner
o o rtio n
76.61
.160
.041
.0004
.024
Amide
N
Basic
N
R esidual
N
.003
.004
.014
.013
.018
.003
.009
.010
P o ta to e s cured and s to re d u n t i l November 27.
Outer
p o rtio n
74.64
.195
.051
.0016
.029
.020
.005
.007
.017
Inner
o o rtio n
77.12
.159
.061
.0002
.037
.016
.005
.012
.028
41
There i s an ap p reciab le d iffe re n c e in some o f th e n itro g e n f ra c tio n s of
th e in n e r and o u te r p o rtio n s of the sweet potato#
found to be h ig h e r i n th e in n e r p o rtio n .
The m oisture co n ten t was
The d a ta i n Table 21 was re c a lc u ­
la te d to th e d ry w eight b a s is and p resen ted i n Table 22.
Table 22.
D is trib u tio n o f n itro g e n in th e in n e r and o u te r p o rtio n s of
th e sweet p o ta to expressed as percentages of the dry weight
a t th e tim e of a n a ly s is .
H arvest sample, October 7 .
T o tal
Outer
p o rtio n
Inner
p o rtio n
NonAlpha
P ro te in Ammonia Amino
N
N
N
Mono
Amino
N
Amide
. N
Basic
N
R esidual
K.
.
..
.697
.145
.012
.047
.012
.016
.055
.050
.684
.175
.002
.103
.077
.013
.038
.045
P o tato es cured and s to re d u n t i l November 27#
Outer
p o rtio n
.769
.201
.006
.114
.079
.020
.028
.069
Inner
p o rtio n
.695
.267
.001
.162
.070
.022
.052
.122
The d a ta i n Tables 21 and 22 show t h a t th e o u te r p o rtio n s were h ig h e r in
t o t a l nitro g en #
The in n e r areas contained a h ig h er percentage of so lu b le non­
p ro te in n itro g e n which i s accounted f o r la r g e ly in th e amino n itro g en f r a c ti o n .
42
Keeping Q u ality o f Sweet P otatoes
Cured Under D iffe re n t Conditions
A l o t o f p o ta to e s was cured f o r 11 days a t 30 °C and a r e la t iv e hum idity
o f 80 to 85 p e rc e n t, and s to r e d f o r fo u r months in a r e f r i g e r a to r a t a
tem perature o f 10 to 12°C and a t a r e l a t iv e hum idity of 80 to 85 p e rc e n t.
These p o ta to e s k e p t com paratively w e ll in sto ra g e during th e 1939-1940
season.
The ends of some of the ro o ts were s h riv e le d , in d ic a tin g an ex­
cessiv e lo s s o f m oisture which probably occurred during th e cu rin g p erio d
although th e ends m erely appeared spongy a t th a t time and became s h riv e le d
la te r.
Figure 1 shows a l o t cured a t 30 °C. and a r e l a t iv e hum idity of 95 to
100 p e rc e n t.
These p o ta to e s kept v ery w e ll and compared w ith a l l o th e r
tre a tm e n ts l o s t th e l e a s t w eight d u rin g th e sto ra g e p e rio d .
fAie e n tir e
lo s s ex p ressed as percen tag e o f th e h a rv e st w eight amounted to 6.35 p e r­
cen t.
There was v e ry s l i g h t evidence of s h riv e lin g and th e p o ta to e s re ­
mained firm th ro u g h o u t th e s to ra g e p erio d .
F igure 2 shows a l o t cured a t 40eC and a r e la tiv e hum idity of 70 to
75 p e rc e n t and s to re d i n a basement a t approxim ately 10 to 12 °C.
The
e f f e c ts o f low h u m id ities d u rin g cu rin g and sto rag e are v ery ev id en t in
t h i s p ic tu r e .
Sweet p o ta to e s cured a t 40 °C. and a r e la tiv e hum idity of 90 to 95
p ercen t and s to re d f o r fo u r months a t 10° to 12 °C and a r e la tiv e hum idity
of 80 to 85 p e rc e n t appeared sound b u t when th ey were examined in te r n a lly
about one h a lf o f the l o t appeared as shown in fig u re 3. The in te r n a l break­
down was noted when the ro o ts were removed from the curing ovens on October 18,
45
and was found i n some o f th e p o tato es from every l o t in th e s e t cured a t
h ig h tem perature and hig h hum idity.
I t was n o t found i n any o f th e l o t s
s u b je c te d to th e o th e r th re e curing c o n d itio n s.
The re g io h o f breakdown was more o r le s s c e n tr a liz e d i n th e tis s u e
j u s t in s id e th e cambium r in g .
The remnants o f th e c e l l s were pure w hite
in appearailce b u t th e t i s s u e surrounding th e c a v itie s and d estro y ed c e l l s
tu rn ed dark v ery r a p id ly when exposed to th e a i r .
Artschwager (7) has d e scrib ed an in te r n a l breakdown th a t he found in
sweet p o ta to e s which had been i n sto ra g e f o r a number o f weeks.
The de­
s c rip tio n and i l l u s t r a t i o n s given by him correspond very c lo s e ly w ith th e
co n d itio n s observed in th e group o f p o ta to e s j u s t d e s c rib e d .
A rtschwager
re fe rre d to th e c a v itie s as “p o ly h ed ral chambers lin e d w ith c o tto n y d e b ris
of th e d is in te g r a te d t i s s u e ” .
He co n sid ered th e mechanism o f t h e i r form­
a tio n m ight be th e same as t h a t in th e lysigenous a i r spaces found i n th e
stem s, le a v e s , and ro o ts o f g ra s s e s , sedges and o th e r p la n ts .
The same
w r ite r suggests t h a t n o tin g th e changes which take p lace under v ario u s
co n d itio n s o f s to ra g e m ight h elp to provide a s a tis f a c t o r y ex p lan atio n
o f th e breakdown.
Only those p o ta to e s cured a t high tem peratures combined w ith high
hum idity showed th e i n te r n a l breakdown.
Therefore i t i s ev id en t t h a t
th e breakdown i s c o r re la te d w ith th e curing co n d itio n s and n o t w ith any
growth p ro c e sse s.
Sweet p o ta to es cured f o r 11 days a t 30°C.
and a r e l a t iv e hum idity of 95 to 100 per­
c e n t. The p ic tu re was taken a f t e r th e
p o tato es had been s to re d in a r e f r ig e r a to r
f o r fo u r months a t 10 to 1£PC. and a r e la ­
tiv e hum idity of 80 to 85 p e rc e n t.
45
F ig .
Sweet p o tato es cured fo r XI days a t 40°C.
and a r e la tiv e hum idity of 70 to 75 p e rc e n t.
The p ic tu re was taken a f t e r th e p o tato es
had been sto re d in a basement f o r fo u r
months a t a tem perature of approxim ately
10 to 15°C.
F ig . 3 .
I n te r n a l breakdovn as seen in the street
p o tato es cured a t 40°C. and a r e la tiv e
hum idity o f 90 to 95 p e rc e n t.
47
SUMMARY AND CONCLUSIONS
Maryland Golden sw eet p o tato es were cured under d if f e r e n t co n d itio n s
o f tem p eratu re and hum idity and placed in s to ra g e .
Chemical analyses were
made and th e keeping q u a litie s noted p e r io d ic a lly throughout the curing
and s to ra g e p e rio d s.
A ra p id h y d ro ly sis o f s ta r c h to sugar occurred during curing and con­
tin u e d l e s s r a p id ly throughout sto ra g e .
The in c re a se in sucrose content
alm ost e n t i r e ly accounted f o r th e in crease in t o t a l su g ars.
sugars showed com paratively l i t t l e change.
Reducing
A marked decrease in th e t o t a l
determ ined carbohydrates occurred during sto rag e when c a lc u la te d as p er­
centages o f th e w eight a t h a rv e st tim e.
An in c re a s e in t o t a l pec t i c m a te ria l was found in a l l l o t s during
th e cu rin g p e rio d .
With th e f i r s t evidence of decay a marked decrease
i n a l l p e c tic c o n s titu e n ts was n o ted .
A d i s t i n c t h y d ro ly sis o f p r o te in occurred in a l l tre atm e n ts during
th e cu rin g p e rio d .
A more ra p id h y d ro ly sis was noted a t th e hig h er
tem peratures and a t th e h ig h er h u m id ities which re s u lte d i n an in c re a se
i n n e a rly a l l o f th e so lu b le f r a c tio n s over th o se cured a t th e lower
tem peratures and h u m id itie s.
d arin g c u rin g .
R esidual n itro g e n in c re a se d in a l l l o t s
In c re a se s were noted in humin and ammonia n itro g e n b u t
both f r a c tio n s were p re s e n t in v ery sm all q u a n titie s .
Lots cured a t
the h ig h er h u m id ities showed th e l e a s t h y d ro ly sis of p r o te in d u rin g th e
subsequent sto ra g e p e rio d .
Amide and b a sic n itro g e n tended to in c re a se
in a l l l o t s during s to ra g e .
The proxim al and d i s t a l halves of the sweet p o ta to were found to
be alm ost i d e n tic a l i n n itro g e n d is tr ib u tio n and c o n te n t.
Comparison
48
o f th e n itro g e n co n ten t o f th e in n e r and o u te r p o rtio n s of the sweet
p o ta to showed th e in n e r p o rtio n to be hig h er in amino n itro g en and
so lu b le n o n -p ro tein n itro g e n b u t lower in t o t a l n itro g e n .
The e f f e c t of hum idity during th e curing p erio d has been shown
*
to be a v e ry im p o rtan t f a c to r i n th e curing p ro cess.
Sweet p o tato es
cured a t 30 °C. and hig h hum idity showed th e l e a s t shrinkage and were
i n th e b e s t co n d itio n a f t e r 4 months of s to ra g e .
A combination of
h ig h tem perature and high hum idity during curing was conducive to an
i n t e r n a l breakdown n o t found under o th er curing co n d itio n s.
49
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51
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52
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_________________
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55
ACKNOWLEDGMENT
The -w riter w ishes to express h is a p p re c ia tio n to Dr* C. 0 .
Appleman o f th e Department o f Botany, U n iv e rsity o f M aryland, f o r
h is guidance and h e lp fu l c ritic is m , during th e course o f t h i s i n ­
v e s tig a tio n and i n th e p re p a ra tio n o f th e m an u scrip t.
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