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Research Article
Re ce ived : 1 Dec embe r 2011 Re vise d: 5 April 2012 Acc epted : 16 April 2012 Published online in W iley O nline Library: 1 June 2012
(wileyonlinelibrary.com) DOI 10.1002/jsfa.5735
Chemical composition and sensory quality of
bovine milk as affected by type of forage andproportion of concentrate in the feed ration
Mette K Larsen,a Ulla Kidmose,b Troels Kristensen,c Pierre Beaumonta
and Grith Mortensena
Abstract
BACKGROUND: The objective of this study was to investigate how some small changes in the forage content of maize andlucerne silage and in the ration between forage and concentrate in the diet of dairy cows affect milk quality. Milk qualitywas assessed by quantitative descriptive sensory analysis and by analysis of tocopherols and carotenoids as well as fatty acid
composition.
RESULTS: Changing the ratio between maize silageand lucerne silagefrom 5 : 1 to 2 : 1 increasedmilk fat content of carotenoids(2327%) and C18: 3 n3 (15%), and reduced stale aroma and creamy flavour. Increasing the proportion of concentrates in thefeed ration from 0.2 to 0.4 increased energy corrected milk yield (26%), reduced fat content (10%), increased C18 fatty acids(862%) and reduced C16(20%) content in milk fat. In addition, this milk type was described bythe sensory panel as lessoily,less saturated and less yellow. The changes in milk composition were related to differences in feed composition.
CONCLUSION: The study revealed the potential to produce milk with a distinct composition and sensory quality based on evensmall changes in the feed composition that are straightforward to implement by farmers.c 2012 Society of Chemical Industry
Keywords: bovine milk; fatty acids; sensory evaluation; antioxidants; feeding
INTRODUCTIONCertain types of forage plants or other feedcomponentsmay influ-
ence milk composition andaffect sensory as well as thenutritional
and technological quality of the dairy products. Additionally such
production conditions may affect the productivity and environ-
mental load. This may be used in the marketing of the produced
dairy products.
Numerous studies have been conducted to assess the effect
of various forage types on the milk composition, especially milk
fatty acid composition.1 5 High contents of polyunsaturated fatty
acids, in particular C18: 3 n3 and conjugated linoleic acid (CLA)
cis9 trans11 in milk fat, are desirable due to positive effects on
human health.
1,6
The main sources of polyunsaturated fatty acidsin normal cow diets are forage, especially grass crops (including
legumes such as clover and lucerne), and oil seeds or oil seed
by-products used as concentrates.1,2,79 Only minor amounts of
the ingested polyunsaturated fatty acids from feed are recovered
in the milk as these fatty acids are hydrogenated to a wide extent
during the ruminal processes.10
A higher content of polyunsaturated fatty acids makes the
milk more susceptible to oxidation, but this oxidation is delayed
to some extent by the inherent content of antioxidants such as
tocopherols, carotenoids and urate.5,1114
Forages as well as oil seeds contain various amounts of
tocopherols and the main source of carotenoids is forage,
especially fresh grass and legumes and silage of grass and
legumes.15 Urate is synthesised during the ruminal processes,
and the amounts are affected by the feed structure.13
The sensory quality of milk is affected by direct transfer of
aroma compounds from feed to milk, but also by formation of
aroma compounds during feed digestion.16The effects of pasture
the composition of milk aroma compounds as well as the sensory
properties have been studied, and milk from cows consuming
pasture has a higher content of a range of aroma compounds,
whereas the sensory properties have been described as more
barny, or more salty, grassy, mothball and less sweet, sweet malty,
sweet aromatic compared to milk from cows fed a total mixed
ration (TMR).1618 CompositionoftheTMRalsoaffectsmilksensory
propertiesandmaizesilagecomparedtograsssilagegivesahigher
Correspondence to: Mette K Larsen, Department of Food Science, Aarhus
University, DK-8830 Tjele, Denmark. E-mail: [email protected]
Present address: VetAgroSup Clermont-Ferrand, Dept of Food Science, Site de
Marmilhat, FR-63370 Lempdes, France.
a Aarhus University, Department of FoodScience,BlichersAll e 20,DK-8830 Tjele,
Denmark
b Aarhus University, Department of Food Science, Kirstinebjergvej 10, DK-5792
Aarslev, Denmark
c Aarhus University, Departmentof Agroecology, Blichers All e 20,DK-8830 Tjele,
Denmark
J Sci Food Agric2013; 93: 9399 www.soci.org c 2012 Society of Chemical Industry
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sweet corn odor and less boiled milk, sour/buttermilk, cardboard
and metallic flavour.3,19 Feeding different lipid sources has only
minor effects on milk sensory properties.5,19,20
These results indicate that the sensory quality of milk is highly
affected by forage composition, i.e. the type of forage as well as
the proportion of forage in the ration. Thus, the hypothesis of the
present work was that milk composition and sensory quality are
affected by even small variations in the proportion of forage and
concentrate as well as the variations in the composition of forage
and concentrates which could be observed between commercial
dairy farms.
EXPERIMENTALAnimals, feeding and production
The experiment involved 72 Danish Holstein cows (mean at start:
86 37 days post partum, 30.1 5.7 kg energy corrected milk
yield) in a traditional production trial with eight treatments in
a balanced 2 2 2 design. Cows were randomly allocated to
treatments (nine cows per treatment) during an experimental
period of four weeks. The treatments were:
Ratio between maize silage and lucerne silage (5 : 1 or 2 : 1,
respectively)
Type of concentrate (barley or beet pulp in combination with
rape seed cake)
Proportion of concentrate (200 or 400 g kg1 of planned dry
matter intake)
Maize was cut when the dry matter content in the total plant
reached 320 g kg1 and ensiled in a bulk silo. Lucerne silage was
from the primary growth and cut when one tenth of the plants
were flowering. After 1 day of wilting in the field plants were
chopped and ensiled in a bulk silo.
All cows were housed in one group with ad libitum access
to one of the four different TMRs (Table 1) through Insentec
feeders (Insentec B.V., Marknesse, The Netherlands) controlling
the individual access and monitoring the intake. In addition, the
cows assigned to the high proportion of concentrate treatments
(400 g kg1 of dry matter intake) were fed 2.2 kg dry matter
rapeseed cake in combination with either 2.2 kg dry matter barley
or 2.2 kg dry matter dried beet pulp at automatic feeding stations
in the barn controlling the individual access and the amount of
feed, the type of concentrate being identical to the type given in
the TMR for the individual cow.
Table 1. Composition (g kg1 of drymatter) of thetotal mixed rationfedad libitum
Maizelucerne ratio 5 : 1 Maizelucerne ratio 2 : 1
Component Barley Beet pulp Barley Beet pulp
Barley 100 100
Beet pulp 100 100
Rapeseed cake 94 94 94 94
Maize silagea 655 655 527 527
Lucerne silageb 135 135 263 263
Urea 6 6 6 6
Mineral 10 10 10 10
a DM 360 g kg1, ash 33, protein 85, starch 320, NDF 390 g kg1 DM.b DM 300 g kg1, ash 128, protein 220, NDF 440 g kg1 DM.
The composition of each TMR fed through the Insentec feeders
was measured daily. Individual intake of TMR as well as additional
concentrates was registered at each feeding bout and daily intake
was calculated. Individual milk recordings were performed six
times during the experimental period representing 24-h milk yield
from an afternoon andthe followingmorningmilking. Milk fatand
protein analysis for registration of production was based on these
samples.
Sampling
Representative samples of each feed component were taken
weekly and were stored at 20 C until analyses of the fatty acid
composition and the content of tocopherols and carotenoids was
performed.
Individual milk samples were collected from two morning
milkings during the last week of the experiment and sub-samples
werefrozen immediately after sampling and stored at20 C until
analyses were performed for contents of tocopherols, uric acid
and carotenoids, fatty acid composition and colour measurement.
For sensory analysis, cows were milked in groups according to
treatments, and a 30 L milk sample was withdrawn from the bulk
milk of eachtreatment. Milk samples were pasteurised (72
C, 15 s)within 6 h after milking, poured into 2-L milk plastic bottles that
were placed in ice water and kept at 1 C until sensory analysis
was carried out the next day.
Chemical analysis
Milk fat and protein contents were analysed using a Milkoscan
4000 (Foss, Hillerd, Denmark). The milk colour was measured
using a Minolta Chroma Meter (Minolta Co. Ltd, Osaka, Japan)
and the CIE (Commision Internationale dEclairage) Lab scale
with standardised daylight (D65). The L, a and b values
reflect lightness (0 = black, 100 = white), redness (100
= green, 100 = red) and yellowness (100 = blue, 100 =
yellow), respectively. The instrument was calibrated against a
white standard plate. Milk (14 mL) was poured into a white
porcelain basin (diameter 45 mm, height 30 mm) and colour was
measured on the liquid surface, i.e. where the front plate of
the instrument just touched the surface. Urate was analysed as
described previously.13
Feed samples were mixed with liquid nitrogen and ground by
use of a domestic coffee grinder to obtain sizes of2 mm length.
Carotenoids and tocopherols were extracted and analysed using
either 1 g ground feed sample or 2 mL milk sample as described
by Slotsetal.,21 with the following modification: HPLC analysis of
carotenoids wascarriedout using a YMCC30 column (YMC Europe
GmbH, Dinslaken, Germany), 250 4.6 mm i.d., 5 m particle size,
operatedatatemperatureof25 C.Isocraticelutionwascarriedout
with ethanol/methanol/tetrahydrofuran (75 : 20 : 5) (v/v/v) with aflow rate of 1 mL min1, and chromatograms were recorded at
450 nm.
For fatty acids analysis, cream was separated from skim milk by
centrifugation (1700 g, 4 C, 20 min), subsequently cream was
centrifuged (13 000 g, 20 C, 10 min) to separate fat. A liquid
fat fraction was obtained by heating at 60 C for 10 min and
centrifugation (13000 g, 40 C, 10 min). Ten milligrams of milk
fat was dissolved in 1 mL pentane and 10 L 12.5 mol L1 sodium
methylate in methanol was added for methylation. Samples were
mixed for1 min andleft for10 min at ambient temperaturebefore
centrifugation (13 000 g, 4 C, 5 min). The supernatant was used
foranalysis by gaschromatography.Fatty acids fromherbage were
isolated and methylated as described by Palmquist and Jenkins.22
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Table 2. Feed intake and effect of ratio between maize and lucerne and share of concentrate on milk production
Proportion of silage,maizelucerne
Amount of concentrate indry matter intake
Effect of silage Effect of amount
Parameter 5 : 1 2 : 1 proportion 20% 40% of concentrate
Feed intake (kg DM day1) 20.2 19.7 NS 18.1 21.7
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Table 3. Effect of ratio between maize and lucerne and share of concentrate on milk composition
Proportion of silage,maizelucerne
Amount of concentrate indry matter intake
Effect of silage Effect of amount
Parameter 5 : 1 2 : 1 proportion 20% 40% of concentrate
Fatty acids (mg g fatty acids1)
Sum C6 C14 19.9 20.0 NS 19.9 20.0 NS
C16 : 0 27.6 29.2
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Table 4. Effect of ratio between maize and lucerne and share of concentrate on sensory attributes
Proportion of silage,maize : lucerne
Amount of concentratein dry matter intake
Effect of Effect of amount
Attibutes 5 : 1 2 : 1 silage proportion 20% 40% of concentrate
Aroma attributes
Creamy aroma 4.2 4.6 NS 4.6 4.2 NS
Metallic aroma 2.7 2.3 NS 2.6 2.4 NS
Cowstable aroma 2.3 2.3 NS 2.1 2.5 NS
Stale aroma 4.0 3.0
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treatments were observed for these compounds. Furthermore,
the loading vector of creamy flavour had high scores of the first
as well as the second PC although this attribute was not affected
significantly by the amount of concentrate which was the main
X variable of the first PC. Thus, several properties which did
not show significant differences in the univariate analysis were
affected by treatments according to the multivariate analysis and
such differentresults shouldbe explainedby the differentnatures
of univariate and multivariate analysis.
Effect of feeding on fatty acid composition
The loadings plot (Fig. 2) shows that higher contents of C18 : 3
n3, C18:2n6 and C18 : 1 in milk fat were directly related to feed
content of these components. The content of C18 : 0 in milk fat
was related to the content of all C18 fatty acids in feed instead
of the content of C18 : 0 in feed, due to the fact that a major part
of the unsaturated fatty acids from feed are hydrogenated in the
ruminal metabolism.10
These findings confirm that the content of unsaturated C18
fatty acids in milk fat can be increased by increasing the content
of these compounds in feed. Apart from supplying the fatty acids,
a higher fat content in feed also reduces rumen hydrogenationwhich gives a higher recovery of C18 : 3n3 and C18: 2n6.7,24 The
main feed source of C18 : 3n3 was lucerne silage, and the content
of this fatty acid in milk fat was higher when the proportion of
lucerne in forage was higher. However, an increased proportion of
concentratealso increasedthe C18: 3 n3 content in milk fat, which
was due toa combinationof C18 : 3 n3 supply from rapeseed cake
and the fat content of rapeseed cake, giving a protection against
hydrogenation.
The content of C18 : 1 trans11 in milk fat was also closely
related to the rapeseed cake because this fatty acid is a product
of partial hydrogenation in the rumen of polyunsaturated C18
fatty acids.10 Higher fat content in rapeseed cake may reduce the
final hydrogenation step and in this way also increase the C18 : 1trans11 content in milk fat. CLA cis9trans11 is mainly formed by
udder desaturation of C18 : 1 trans11 and these two fatty acids
were closely related as commonly found.2 Other research has
reported a higher content of C16 in milk fat from cows fed maize
silage and higher contents of C18 : 0, C18 : 1 and C18 : 3 n3 in
milk fat are observed when cows are fed lucerne silage due to a
higher fat content in the lucerne based feed.25 Lucerne has also
been reported to create more stable rumen environments where
hydrogenation is more complete.26This results in a higher content
of C18 : 0 in milk fat; however, the content of C18 : 3n3 in milk fat
is still elevated due to the higher feed content of this fatty acid.26
As shown in Fig. 2, the milk fat content was negatively related
to thefeedcontent of rapeseed cake. This mightbe dueto a slight,
non-significant milk fat depression caused by the higher contentof unsaturated fat in the rapeseed cake.2,9
The content of C16 in milk fat was not related to the feed
content of C16 because this fatty acid is also de novosynthesised.
It is evident that a lower supply of fat from feed leads to a higher
de novosynthesis.9,27
Effect of feeding on antioxidants
Tocopherolsand carotenoids in the feed were closely correlated to
identical compounds in milk (Fig. 2). These findings confirm that
the milkcontents of tocopherols and carotenoids can be increased
by increasing the feed content of these compounds. Figure 2 also
reveals that the main feed source of carotenoids was lucerne
silage, which, as well as rapeseed cake, was the major source
of -tocopherol, while rapeseed cake was the most important
source of-tocopherol. The levels of tocopherol and carotenoids
in milk were similar to values in milk fromcows fed maize silage.12
When feed concentrations of carotenoids and tocopherols are
enhanced, the effects on milk content decreases as only a limited
amountof carotenoids andtocopherols canbe secreted in milk on
a daily basis.15,28 The present study indicated that concentrations
of antioxidants were relatively low, and this explains the positive
relationshipbetween thecontentof antioxidantsin feed andmilk.
Effect of feeding on sensory characteristics
Milk yellow colour (b values) were positively affected by higher
lucerne amounts as well as higher forage intake, and to some
extent related to carotenoids; however, more specifically related
to fat. Similarly, yellow colour (b values) are reported to be related
to carotenoid content of milk and feed content of grass products,
however, other components such as riboflavin also affect the
colour, and therefore, yellow colour (b values) cannot directly
predict-carotene content.15,17,29,30
The visual sensory attributes (yellowness, saturation and oilyappearance) were closely connected and were related to creamy
aroma, fat content, yellow and white colour (b and L values)
(Fig. 2). These attributes were associated with high forage levels.
In contrast, high concentrate levels were associated with cow
stable aroma. This was not in accordance with previous results
in which milk from grazing cows has a more barny, salty and
grassy flavour than milk from cows fed a total mixed ration, which
has a sweeter and more malty flavour.17,18 Feeding with maize
has led to a higher intensity of cream flavour, maize odour and
sweet corn flavour, whereas grass silage has led to an increased
intensity in boiled milk flavour, sour flavour, cardboard flavour
and metallic taste.3 Although grass silage and the attribute maize
flavour were not included in the study, the higher intensity of
creamy flavour with increased maize silage was in accordancewith previous results.3
The results show that milk composition including sensory
properties were affected by composition of forage as well as
proportion of forage to concentrate, whereas the different types
of concentrate did not affect milk quality. This knowledge can be
used to develop guidelines for feeding of dairy cows targeted at
production of milk with distinct properties. If such type of milk
is used for production of dairy products, product composition as
wellas sensory properties includingappearance could be affected.
ACKNOWLEDGEMENT
This projectwas fundedby the Danish Ministry of Food, Agricultureand Fisheries and by the Danish Cattle Federation.
REFERENCES1 Dewhurst RJ, Shingfield KJ, Lee MRF and Scollan ND, Increasing the
concentrations of beneficial polyunsaturated fatty acids in milkproduced by dairy cows in high-forage systems. Anim Feed SciTechnol131:168206 (2006).
2 Grummer RR, Effect of feed on the composition of milk-fat.J Dairy Sci74:32443257 (1991).
3 Mogensen L, Vestergaard JS, Frette X, Lund P, Weisbjerg MR andKristensen T, Effect of toasting field beans and of grass-clover:Maizesilage ratioon milk production,milk compositionand sensoryquality of milk.Livest Sci128:123 132 (2010).
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