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J Sci Food Agric 1998, 76, 546È552
Eþect of Naked Oats in the Dairy Cow’s Diet on
the Oxidative Stability of the Milk Fat
Anna M Fearon,1* C Sinclair Mayne2 and Colin T Charlton3
1 Department of Food Science, The Queen’s University of Belfast, and the Food Science Division,
Department of Agriculture for Northern Ireland, Newforge Lane, Belfast, BT9 5PX, UK
2 Agricultural Research Institute for Northern Ireland, Hillsborough, Co. Down. BT26 6DR, UK
3 Food Science Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast,
BT9 5PX, UK
(Received 15 January 1997 ; revised version received 26 June 1997 ; accepted 7 August 1997)
Abstract : Oxidative stability of milk fats from cows o†ered naked oats- and
barley-based diets were compared in shelf-life tests using the Schaal Oven Test at
63¡C, and determination of peroxide and thiobarbituric acid values. Milk fat
from cows o†ered the diet containing naked oats, although containing a higher
proportion of monounsaturated fatty acids, had a signiÐcantly longer oxidation
induction period (13 days) than milk fat from cows o†ered the control (barleybased) diet (9 days). However, sensory testing of the milk fats indicated that a
perceptible odour di†erence was apparent between stored (63¡C) and unstored
milk fats after 3 days of storage irrespective of the diet fed. It is possible that the
odours perceived may have originated from the cowsÏ diets or from hydrolytic
rancidity reactions. The difficulties of relating chemical and sensory testing of the
oxidative deterioration of milk fat or butter are underlined. ( 1998 SCI.
J Sci Food Agric 76, 546È552 (1998)
Key words : milk fat ; dietary modiÐcation ; oxidative stability
INTRODUCTION
acid composition of the dietary material. The presence
of oleic acid (C
) in the milk fat results primarily
18 > 1
from the conversion of C
to C
by the bovine
18 > 0
18 > 1
desaturase enzyme system located in the intestine and
mammary gland (Kinsella 1972). In order to produce a
milk fat with a higher proportion of unsaturated fatty
acids, it is necessary either to increase the content of
unsaturated fatty acids entering the blood stream from
the rumen and supplying the mammary gland, or, to
optimise the desaturating ability of the intestine and
mammary gland (Banks and Christie 1990).
The Ðrst approach was adopted by Australian scientists in the early 1970s, with the feeding of unsaturated
lipid encapsulated within a formaldehydeÈprotein
matrix (Scott et al 1970). The technique not only protected the dietary lipid from hydrogenation in the
rumen but avoided interference with normal rumen
activity. Early problems with the highly unsaturated
nature of the resulting milk fat ([20% linoleic acid,
There has been considerable interest in dietary modiÐcation of the fatty acid composition of cowsÏ milk fat to
increase the content of unsaturated acids present and
hence improve the physical properties of the fat. The
short- and medium-chain fatty acids (C to C and a
4
14
proportion of C ) in cowsÏ milk fat are synthesised de
16
novo in the mammary gland. The longer chain acids
(some C and the C acids) are derived directly from
16
18
the diet and it is their proportions in the milk fat that
may be altered by modifying the lipid portion of the
cowsÏ diet (Hawke and Taylor 1983). Dietary lipid normally undergoes enzymatic hydrolysis and biohydrogenation in the cowsÏ rumen, with the
consequence that stearic acid (C
) is the principal
18 > 0
fatty acid leaving the rumen, irrespective of the fatty
* To whom correspondence should be addressed.
546
( 1998 SCI.
J Sci Food Agric 0022È5142/98/$17.50.
Printed in Great Britain
Oxidative stability of dietary modiÐed milk fat
C
) led to rapid oxidative deterioration, but these
18 > 2
have largely been resolved with improved technology,
the inclusion of substantial quantities of a-tocopherol in
the diet and the use of rapeseed (canola) as the lipid
source (Goering et al 1976 ; Ashes et al 1992).
The alternative approach has been to o†er dairy cows
high lipid-containing cereals or oilseeds in order to
provide a rich supply of C
fatty acids to the
18
mammary gland for subsequent desaturation and
incorporation into milk fat as C
. In this study,
18 > 1
naked oats were used as the high-lipid source, resulting
in a milk fat having an increased proportion of C
18 > 0
and C
fatty acids and producing a softer, more
18 > 1
spreadable butter (Fearon et al 1996). This present work
aimed to determine whether the increased content of
monounsaturated fatty acids adversely a†ected the oxidative stability of the milk fat.
EXPERIMENTAL
Sample preparation
Twenty Friesian dairy cows in early lactation were
divided into two groups and o†ered either naked oatsor barley-based (control) concentrates and silage ad
libitum in a continuous design experiment of 10 weeks
duration. Full details of the experimental design and
diet formulation have been described by Fearon et al
(1996). Milk was collected from each group weekly ;
547
separated into cream and churned into butter. Fatty
acid composition of the milk fats, as determined by
methylation and subsequent analysis by gasÈliquid
chromatography (Fearon et al 1996), is given in Table 1.
Milk fat compositions were found not to di†er signiÐcantly between weeks during the 10 weeks of the feeding
trial period (Fearon et al 1996) ; therefore, for the purposes of this study the weekly butter samples were identiÐed as replicates.
Storage stability tests
Portions of butter (approximately 250 g), representative
of both diets, were randomly selected from the butters
produced over the trial period to give three replicates
per diet. These were placed in 1000 cm3 opaque white
plastic food-grade containers (Polar-cup, Portadown,
Northern Ireland) in an incubator at 20 ^ 1¡C. The
Schaal Oven Test was conducted using clariÐed butter
oils prepared from similar butter sources (BS 769 : 1961).
Aliquots of the butter oil (800 cm3) were placed in
1000 cm3 amber glass beakers in a laboratory oven at
63 ^ 1¡C (Rossell 1983).
Peroxide value measurements
Peroxide value (PV) measurements were carried out in
triplicate at 3-day intervals on the stored butter and
butter oil samples. These were determined by the AOCS
TABLE 1
Fatty acid compositiona (g kg~1) of milk fats from dairy cows o†ered barley-based (control)
and naked oats-based concentrates and a-tocopherol content of concentrates
(Values are means of Ðve observations per week over 10 weeks)
Fatty acid
Barley-based
concentrates
Naked oats-based
concentrates
SEM
SigniÐcance of
treatment e†ect :
Concentrates type
4:0
6:0
8:0
10 : 0
12 : 0
14 : 0
14 : 1
16 : 0
16 : 1
18 : 0
18 : 1
18 : 2
a-Tocopherol content
of concentratesb
(kg g~1)
29É4
17É1
12É9
29É1
33É0
114É8
13É7
329É8
19É2
110É5
224É6
13É0
33É9
16É9
11É7
24É3
26É2
98É1
11É4
279É3
17É0
139É3
272É9
13É3
0É53
0É14
0É15
0É58
0É87
1É85
0É73
5É09
0É12
2É08
4É01
0É17
*
NS
**
**
**
**
NS
**
**
***
***
NS
15É6
15É6
a Fearon et al (1996).
b Base level 7 mg kg~1 (BlanchÑower, personal communication).
*** P \ 0É001, ** P \ 0É01, * P \ 0É05, NS, not signiÐcant.
548
Official Method Cd 8-53 (AOCS 1990) and results
expressed as milliequivalents peroxide per kg sample.
2-Thiobarbituric acid value measurements
Thiobarbituric acid value (TBA) measurements were
carried out in triplicate at 3-day intervals on the stored
butter and butter oil samples. TBA values were determined by the method of Tarladgis et al (1960) using the
modiÐed distillation apparatus described by Hoyland
and Taylor (1989), with 50 cm3 of distillate being collected within 10 min. Absorbance readings at 538 nm
were converted to mg malonaldehyde per kg sample by
multiplying by 7É8 (Pearson 1976).
A M Fearon, C S Mayne, C T Charlton
Duo-trio test
The duo-trio test (BS 5929 : Part 2, 1992) was employed
to assess if an odour di†erence could be perceived
between unstored standard butter oils and butter oils
stored for di†erent periods at 63¡C. Thirty-two panellists were presented with an identiÐed reference sample
followed by two coded samples, one of which was identical to the reference sample and the other di†erent. The
panellists were asked to smell all three samples and
identify which of the coded samples di†ered from the
reference sample. Each comparison was balanced so
that 16 panellists received the standard oil (unstored) as
the reference sample and 16 panellists received a treated
oil (stored at 63¡C) as the reference sample. Assessments
with butter oils from each diet were carried out separately 7 days apart.
a-Tocopherol content
Statistical analysis
The barley- and naked oats-based concentrates were
analysed for a-tocopherol content using the extraction,
saponiÐcation and chromatographic methods described
by McMurray and BlanchÑower (1979). The highperformance liquid chromatography system (HPLC)
was supplied by Merck Ltd (Poole, Dorset) and comprised a Hitachi L6000 pump, F1050 Ñuorescence detector, AS2000 autosampler and Hewlett Packard 3392
integrator. A Lichrosorb RP18 (5l) 250 ] 4 mm
column (Merck Ltd, Poole, Dorset, UK) was used with
98% methanol as the mobile phase and a Ñow rate of
1É8 cm3 min~1.
BS 5929 : Part 2 (1992) was applied to the sensory
results to determine signiÐcance of di†erence between
treatments and standards. Analysis of variance was
carried out on peroxide value and TBA value results.
Gompertz curves (Bliss 1970) were Ðtted to the PV and
TBA results plotted against time (days of storage). The
Gompertz curve is an asymmetrical sigmoidal curve
which has the form
y \ a ] c* exp([exp(exp([b(t [ m))))
(1)
where y is the PV or TBA value at time t, and a, c, b
and m are parameters to be estimated.
Sensory analysis
RESULTS AND DISCUSSION
Samples
A large volume (4000 cm3) of clariÐed butter oil from
each dietary treatment was prepared (BS 769 : 1961),
sub-divided into four portions per diet in amber
2000 cm3 glass beakers and held at 63 ^ 1¡C in laboratory ovens for 3, 8, 13 and 21 days to give a range of
peroxide values. The samples were dispensed as 10 cm3
aliquots into capped amber glass vials and presented at
a temperature [40¡C to the panellists for assessment.
Unstored clariÐed butter oils from both diets were
heated to 63¡C as standards for assessment.
Sensory unit
The sensory evaluation of the butter oils was undertaken in a sensory evaluation suite with each panellist
in an individual booth with positive air Ñow vented to
the outside of the building. Samples were presented in
amber glass vials and evaluated under red lighting
adjusted so that appearance di†erences between treatments were masked. The questions were delivered and
responses analysed on a computerised system using
PSA software, version 1.636 (Oliemans, Punter and
Partners BV, Burgemeester, Utrecht, Netherlands).
The high-lipid dietary material used in this study was
naked oats, a cereal commonly containing twice as
much lipid as other cereals grown in the UK, with a
lipid content up to 80È100 g kg~1 dry matter
(Valentine 1987) and approximately half of the fatty
acids present are unsaturated (Morrison 1977). Other
dietary materials used as rich sources of C fatty acids
18
have been soya beans and whole and ground rapeseed
(Banks et al 1980 ; Murphy et al 1990). These high-lipid
cereal sources not only provide the necessary substrate
(C
) for the bovine desaturase enzyme but retention
18> 0
of the seed coat serves to minimise any adverse e†ect of
the dietary oil on the activity of rumen microorganism
(Banks and Christie 1990). The milk fats from cows
o†ered high-lipid cereal sources have contained
decreased contents of C
,C
and C
fatty acids
12> 0 14> 0
16> 0
and increased contents of C
and C
fatty acids,
18> 0
18>1
resulting in softer milk fats with lower solid fat contents
at low temperatures (Murphy et al 1990 ; Fearon et al
1996). It is recognised that fats or oils containing a
higher proportion of unsaturated fatty acids have a
shorter shelf-life due to the more rapid oxidation of
Oxidative stability of dietary modiÐed milk fat
unsaturated fatty acids (Rossell 1989). Sonntag (1979)
described the relative oxidation rates of linolenic
(C
) : linoleic (C
) : oleic (C
) : stearic (C
)
18> 3
18> 2
18>1
18> 0
fatty acids as 150 : 100 : 10 : 1. It was hoped in the
present work that improvement of the functional characteristics of milk fat, by increasing the proportion of
monounsaturated fatty acids, would be achieved
without a serious deterioration in oxidative stability of
the fat.
The resistance of the butters and butter oil samples to
oxidative deterioration was measured by shelf-life tests
at ambient and high temperatures. Stability testing at
room temperature has the disadvantage of being very
slow ; in this study no peroxides were detected and only
low TBA values, between 0É01 and 0É2 mg malonaldehyde per kg, were determined in the butters stored at
20¡C during the storage period (Table 2). These results
were in agreement with those of Farag et al (1990) who
reported little change in PV and TBA values of butters
stored at room temperature (unspeciÐed) for 18 days.
The butter samples held at 20¡C had not been clariÐed
and, as they contained O16% moisture, it must be
acknowledged that deterioration, other than oxidation
may have taken place. For example, hydrolytic rancidity with the formation of free fatty acids may have
occurred.
Accelerated methods of testing the shelf-life of lipidcontaining products have been reviewed by Rossell
(1983) and Frankel (1993). The Schaal Oven Test
employed here was originally devised by the cracker
and biscuit industry. It is a simple, uncomplicated test
using heat as an accelerant of oxidation and can be
expected to provide a reasonable comparison between
samples subjected to the same test conditions (Rossell
1983 ; Frankel 1993). The course of oxidation was followed in the butter oil samples by testing aliquots of oil
at regular intervals using PV and TBA determinations.
The initial stage of very slow oxidation (the induction
period) can be measured as the time required to reach
549
an end point of oxidation corresponding either to a
level of detectable rancidity (a deÐned peroxide value)
or, as in this study (Figs 1 and 2), to a sudden change in
oxidation rate. Graphs of peroxide values and TBA
values for butter oils held at 63¡C are shown in Figs 1
and 2, respectively. Gompertz curves were Ðtted to the
TBA and PV results for the butter oils and the conclusion of the induction phase was identiÐed by drawing a
line tangential to the point of inÑexion to cut the lower
asymptote.
The signiÐcance of the di†erence between the duration of the initial lag or induction phases of the clariÐed
milk fats (butter oils) from the di†erent dietary treatments was tested. Results are presented in Table 3 and
show that there was a highly signiÐcant (P \ 0É01) difference in the length of the induction phase between
milk fats obtained from cows o†ered barley-based or
naked oats-based concentrates, with the milk fat from
the naked oats diet having a longer induction period.
The TBA values showed a similar trend with a very
highly (P \ 0É001) signiÐcant longer induction phase for
milk fat originating from cows receiving a naked oatsbased diet. For both sets of data the actual values for
the duration of the induction phase as identiÐed from
the PV and TBA graphs were similar, approximately 9
days for milk fats from cows o†ered the control barleybased diet, and 13 days for milk fats from cows o†ered
the diet containing naked oats.
In the early stages of oxidation any antioxidants
present in a lipid-containing product will play a role in
inhibiting or delaying the onset and progress of oxidation. By the end of the induction period, however, the
antioxidant molecules will all have been involved in
reactions. Although antioxidants were not added to the
milk fats, it is acknowledged that tocopherols, in particular a-tocopherol, will be transferred to milk fat from
the cowsÏ diet (Hidiroglou 1989 ; Nicholson and St
Laurent 1991). An inverse relationship has been reported between susceptibility of milk to oxidised Ñavour
TABLE 2
Peroxide values (PV) (mEq peroxide kg~1) and thiobarbituric acid (TBA) values (mg malonaldehyde kg~1) of butters prepared from milk from cows o†ered barley or naked oats-based
diets, and stored at 20¡C
Storage period
(days)
0
1
8
15
22
a ND, not detected.
Barley-based (control) concentrates
Naked oats-based concentrates
PV
T BA
PV
T BA
NDa
ND
ND
ND
ND
0É00
0É00
0É078
0É078
0É156
ND
ND
ND
ND
ND
0É00
0É00
0É078
0É078
0É156
A M Fearon, C S Mayne, C T Charlton
550
Fig 1. Gompertz curves Ðtted to peroxide values (PV) for
clariÐed milk fats stored at 63¡C from cows o†ered barley
(È = È) or naked oat-based (È È…È È) concentrates.
Fig 2. Gompertz curves Ðtted to thiobarbituric acid (TBA)
values for clariÐed milk fats stored at 63¡C from cows o†ered
barley (È = È) or naked oats-based (È È…È È) concentrates.
and tocopherol content (Schingoethe et al 1978). Therefore, it was necessary to eliminate the possibility of the
dietary cereal sources contributing di†ering amounts of
a-tocopherol by analysing the prepared concentrates.
Both the barley- and the naked oats-based concentrates
contained 15É6 kg g~1 a-tocopherol (Table 1). However,
it has been reported that oats contain other antioxidant
compounds in the form of esters of phenolic acids,
which were found to be e†ective at increasing the oxidative stability of a vegetable oil system (Duve and White
1991). Nevertheless, although this may be one possible
explanation for the di†erences observed in induction
phase duration of the milk fats, it was not determined in
this experiment if these phenolic compounds were transferred into the milk fat.
Results from the sensory assessment of the butter oils
are presented in Table 4. Assessors were asked to identify which of two coded samples smelled di†erently from
a reference sample. Statistical analysis of the results
tested if the number of correct replies was statistically
signiÐcant (Table 4). It was found, irrespective of the
cereal content of cowsÏ diet, that following storage at
63¡C for 3 days, a perceptible di†erence in odour could
be detected between stored and unstored milk fats. This
period of storage (3 days) corresponded to PVs
\4É0 meq kg~1 and is in agreement with the work of
Downey (1974) who observed perceptible odour development in milk fats having PVs as low as
O2 meq kg~1. (In the sensory assessment the milk fat
originating from cows on the barley diet was not compared directly with those milk fats from cows on the
naked oats diet. Instead the storage periods at 63¡C
which produced a perceptible change in odour for each
milk fat were identiÐed.) The 3 days storage period
however, contrasts markedly with the end of the induction phases as determined by TBA and PV analyses,
which were approximately 9 days and 13 days for milk
fats from barley- and naked oats-based concentrates,
respectively. Nevertheless, the lower level of signiÐcance
TABLE 3
Duration and statistical signiÐcance of di†erence between induction phases identiÐed from Gompertz
curves Ðtted to peroxide values (PV) and thiobarbituric acid values (TBA) for clariÐed milk fats from
dairy cows o†ered barley (control) or naked oats-based concentrates
Diet treatment
Barley (control)
Naked oats
Statistical signiÐcance of
di†erencea
PV (mEq peroxide kg~1)
T BA (mg malonaldehyde kg~1)
Induction phase
(day)
SE
Induction phase
(day)
SE
9É56
12É85
0É006
0É607
0É653
(P \ 0É01)
8É84
13É26
0É0002
0É489
0É470
(P \ 0É001)
a t value \ (induction [ induction /J(SE )2 ] (SE )2.
1
2
1
2
Oxidative stability of dietary modiÐed milk fat
551
TABLE 4
Results of duo-trio di†erence test for sensory assessment of odour di†erence of clariÐed
milk fats obtained from cows o†ered barley or naked oats-based concentrates and stored
at 63¡C
T reatment
(days at 63¡C)
3 (PV \ 4)
8 (PV 6È8)
13 (PV 10È15)
21 (PV [ 20)
Barley vs standard
Naked oats vs standard
Correct repliesa
SigniÐcanceb
Correct repliesa
SigniÐcanceb
29/32
24/32
26/32
25/32
P \ 0É001
P \ 0É01
P [ 0É001
P \ 0É001
22/32
21/32
26/32
28/32
P \ 0É05
NS
P \ 0É001
P \ 0É001
a Panellists could identify odour di†erence between treated (stored at 63¡C) and standard
(unstored) milk fats.
b Level of signiÐcance (BS 5929, 1992) was stated as 26/32 (P \ 0É001), 24/32 (P \ 0É01),
22/32 (P \ 0É05) and less than 22/32 (not signiÐcant).
c PV, peroxide value, mEq peroxide kg~1.
at day 3 (P \ 0É05) and day 8 (not signiÐcant) for milk
fat from the naked oats diet is in keeping with the
order observed with the chemical indices of oxidation
(Table 2).
There are several factors which should be considered
when interpreting these results. In the duo-trio test, the
assessors were presented with an identiÐed reference,
thus reducing the need for expert or selected assessors
(Kilcast 1995). However, the assessors, although receiving some training, were not experienced in identifying
or describing oxidative o†-Ñavours, and it was therefore
difficult to interpret whether the odour di†erence they
perceived was due to oxidative o†-Ñavour development
or to odour contributions from other sources. For
example, volatiles originating from the cereal (Urbach
1990) or from hydrolytic rancidity reactions (Downey
1974 ; Deeth, Fitzgerald and Wood 1979) which may
become more dominant or pronounced with prolonged
heating at 63¡C. Nevertheless, from this study the inclusion of naked oats in the diet of dairy cows would seem
to be an e†ective means of modifying the composition
of milk fat, enhancing its functional properties (Fearon
et al 1996) whilst not adversely a†ecting the oxidative
stability of the fat. Apparent discrepancies between the
sensory testing and chemical indices of oxidation underlined problems associated with correlating such tests,
although both were in agreement with the order of stability of the milk fats.
ACKNOWLEDGEMENTS
The authors wish to thank Dr Linda Farmer and the
sta† of the Sensory Evaluation Unit for their assistance
with this work.
REFERENCES
AOCS 1990 Sampling and Analysis of Commercial Fats and
Oils. Peroxide V alue (Official Method Cd 8-53). American
Oil Chemists Society, Chicago, USA.
Ashes J R, St Vincent Welch P, Gulati S K, Scott T W,
Brown, G H 1992 Manipulation of fatty acid composition
of milk by feeding protected canola seeds. J Dairy Sci 75
1090È1096.
Banks W, Christie W W 1990 Feeding cows for the production of butter with good spreadability at refrigeration
temperatures. Outlook Agric 19 43È47.
Banks W, Clapperton J L, Kelly M E 1980 E†ect of oil
enriched diets on the milk yield and composition, and on
the composition and properties of the milk fat, of dairy
cows receiving a basal ration of grass silage. J Dairy Res 47
277È285.
Bliss C I 1970 Statistics in Biology (Vol 2), Mcgraw-Hill, New
York, pp 194È205.
Deeth H C, Fitzgerald C H, Wood A F 1979 Lipolysis and
butter quality. Aust J Dairy T echnol 34 146È149.
Downey W K 1974 Butter Quality. An Foras Taluntis, Dublin,
Republic of Ireland.
Duve K J, White P J 1991 Extraction and identiÐcation of
antioxidants in oats. J Am Oil Chem Soc 68 365È370.
Farag R S, Ali M N, Taha S H 1990 Use of some essential oils
as natural preservatives for butter. J Am Oil Chem Soc 68
188È191.
Fearon A M, Mayne C S, Marsden S 1996 The e†ect of inclusion of naked oats in the concentrate o†ered to dairy cows
on milk production, milk fat composition and properties. J
Sci Food Agric 72 273È282.
Frankel E N 1993 In search of better methods to evaluate
natural antioxidants and oxidative stability in food lipids.
T rends Food Sci T echnol 4 220È225.
Goering H K, Gordon C H, Wrenn T R, Bitman J, King R L,
Douglas Jr F W 1976 E†ect of feeding protected safflower
oil on yield, composition, Ñavour and oxidative stability of
milk. J Dairy Sci 59 (3) 416È425.
Hawke J C, Taylor M W 1983 Developments in Dairy
ChemistryÈ2 : L ipids, ed Fox P F. Applied Science Publishers, London, UK, pp 37È81.
552
Hidiroglou M 1989 Mammary transfer of Vitamin E in dairy
cows. J Dairy Sci 72 1067È1071.
Hoyland D V, Taylor A J 1989 A modiÐed distillation method
for the detection of oxidation in foods. Int J Food Sci
T echnol 24 153È161.
Kilcast D 1995 Food T aints and O†-Flavours, ed Saxby M J.
Blackie Academic and Professional, London, UK, pp 1È40.
Kinsella J 1972 Stearyl CoA as a precursor of oleic acid and
glycerolipids in mammary microsomes from lactating
bovine : Possible regulatory step in milk triglyceride synthesis. L ipids 7 349È353.
McMurray C H, BlanchÑower W J 1979 Determination of
a-tocopherol in animal feedstu†s using high-performance
liquid chromatography with spectroÑuorescence detection.
J Chromatogr 176 488È497.
Morrison W R 1977 Cereal lipids. Proc Nutr Soc 36 143È148.
Murphy J J, McNeill G P, Connolly J F, Gleeson P A 1990
E†ect on cow performance and milk fat composition of
including full-fat soya beans and rapeseeds in the concentrate mixture for lactating dairy cows. J Dairy Res 57 295È
306.
Nicholson J W G, St-Laurent A M 1991 E†ect of forage type
and supplemental dietary Vitamin E on milk oxidative stability. Can J Anim Sci 71 1181È1186.
Pearson D 1976 T he Chemical Analysis of Foods (7th Edn),
Churchill Livingstone, Edinburgh, UK, pp 494È495.
A M Fearon, C S Mayne, C T Charlton
Rossell J B 1983 Rancidity in Foods, ed Allen J C & Hamilton
R J. Applied Science Publishers, London, UK, pp 21È46.
Rossell J B 1989 Intermediate shelf life products as illustrated
by fats and fatty foods. Food Sci T echnol T oday 3 235È240.
Schingoethe D J, Parsons J G, Ludens F C, Tucker W L,
Shave H J 1978 Vitamin E status of dairy cows fed stored
feed continuously or pastured during summer. J Dairy Sci
61 1582È1589.
Scott T W, Cook L J, Ferguson K A, McDonald I W, Buchanan R A, Loftus Hills G 1970 Production of polyunsaturated milk fat in domestic ruminants. Aust J Sci 32 291È293.
Sonntag, N O V 1979 BaileyÏs Industrial Oil and Fat Products
(Vol 1, 4th edn), ed Swern D. J Wiley and Sons, Chichester,
UK, pp 99È176.
Tarladgis B G, Watts B M, Younathan M T, Dugan L 1960 A
distillation method for the quantitative determination of
malonaldehyde in rancid foods. J Am Oil Chem Soc 37 44È
48.
Urbach G 1990 E†ect of feed on Ñavour in dairy foods. J
Dairy Sci 73 3639È3650.
Valentine J 1987 Breeding cereals of high nutritional quality
with special reference to oats and naked oats. Asp Appl Biol
15 541È548.
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