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- Juhlin, Jessica
(författare)
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Factors associated with spontaneous oxidized flavour in cow´s milk
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spontaneous oxidized flavour (SOF) is an off-flavour in milk that has received attention in only a few countries, primarily due to lack of monitoring. The poly unsaturated fatty acids in milk are considered to make it more prone to oxidize, with effects like shorter shelf life of dairy products and a reduction in consumer acceptance of milk. On the other hand, unsaturated fatty acids have a reputation of being healthier than the saturated fatty acids. Means to optimize the fatty acid composition of milk include breeding measures, why acyl-CoA:diacylglycerol acyltransferase1 (DGAT1), a major gene for milk fat content, has lately attracted a lot of research efforts. The risk of milk to develop SOF showed a strong and positive association with milk concentrations of both the well known prooxidant copper and its substrate the poly unsaturated milk fatty acids. The observed statistical interaction between copper and fatty acid composition suggests that SOF will not develop as easily in milk with high copper content unless sufficient amounts of substrate is available to promote the oxidation process. Breed and selection for fat content had an effect on the composition of milk fat where milk from Swedish Holstein cows generally had larger amounts of poly unsaturated fatty acids compared to the Swedish Red cows in the two selection lines in the SLU research herd. Selection for high milk fat content was associated with lower concentration of conjugated linoleic acid (CLA). The selection for fat content created differences in allele frequencies of the DGAT1 gene between selection lines, with a higher frequency of the 232A allele within the low fat line. DGAT1 genotype was associated with both composition of milk fat and occurrence of SOF, with the A allele being associated with a higher proportion of the polyunsaturated fatty acid CLA and an increased susceptibility of milk to develop SOF. The observed genetic variation in occurrence of SOF indicates that it may become a milk quality issue should bulls become selected that happen to carry genotypes predisposing for milk sensitive to oxidation.
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- Juhlin, Jessica, et al.
(författare)
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Factors relating to incidence of spontaneous oxidized flavor and copper in cow's milk
- 2010
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Ingår i: Acta Agriculturae Scandinavica, Section A - Animal Science. - : Informa UK Limited. - 0906-4702 .- 1651-1972. ; 60, s. 94-103
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Tidskriftsartikel (refereegranskat)abstract
- The incidence of spontaneous oxidized flavor (SOF) is commonly assumed to be dependent on the combination of substrate supply and contents of pro- and anti-oxidants in milk. A total of 142 cows in the experimental herd at the Swedish University of Agricultural Sciences were included, 87 of the Swedish Red breed and 55 of the Swedish Holstein breed. Altogether 893 milk samples were analyzed for milk composition, copper content, and milk flavor. Milk copper concentration was highest in early lactation and during the spring period. Oxidative off-flavor was most common during the first 3 weeks of lactation. However, when adjusting for copper concentration the odds ratio for incidence of SOF was instead highest in lactation weeks 14-39. The higher incidence of SOF during the first 3 weeks of lactation is proposed to be a consequence of the high copper concentration in milk during this period.
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- Juhlin, Jessica, et al.
(författare)
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Relative impact of alpha-tocopherol, copper and fatty acid composition on the occurrence of oxidized milk flavour
- 2010
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Ingår i: Journal of Dairy Research. - 0022-0299 .- 1469-7629. ; 77, s. 302-309
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Tidskriftsartikel (refereegranskat)abstract
- The oxidative process in milk fat, resulting in spontaneous oxidized off-flavour (SOF), is commonly assumed to depend on contents of pro- and antioxidants in milk and availability of fatty acids acting as their substrate. An important antioxidant in milk is alpha-tocopherol whereas the most potent prooxidant is the metal ion copper. The separate effects of alpha-tocopherol, copper, and milk fatty acid profile, and their combined effect on SOF development were examined in milk from 44 multiparous cows fed different roughage types and different amounts of dietary, unsaturated fat. A clear association between concentrations of copper and poly-unsaturated fatty acids in milk and the risk for developing SOF was found. Heritability estimates suggest that occurrence of SOF is partly under genetic control which indicates that milk quality may be compromised if breeding bulls are selected that carry genotypes predisposing for milk prone to develop SOF.
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- Pickova, Jana, et al.
(författare)
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Association of DGAT1 genotype, fatty acid composition, and concentration of copper in milk with spontaneous oxidized flavor
- 2012
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Ingår i: Journal of Dairy Science. - : American Dairy Science Association. - 0022-0302 .- 1525-3198. ; 95, s. 4610-4617
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Tidskriftsartikel (refereegranskat)abstract
- In 136 cows with altogether 969 milk samples, we investigated the effect of the acyl-coenzyme A:diacylglycerol acyltransferase 1 (DGAT1) K232A polymorphism on milk fatty acid (FA) composition and how, in combination with copper concentration in milk, this influences the occurrence of spontaneous oxidized flavor. All milk samples were analyzed for concentrations of copper and individual FA and subjected to sensory analysis by trained judges. We found an effect of DGAT1 genotype on FA composition where mainly the long-chain FA were affected. The 232A allele was associated with larger proportions of the C18:2 cis-9,trans-11 conjugated linoleic acid and lower proportions of C16:0 FA. Milk concentrations of unsaturated FA and copper showed strong and unfavorable associations with spontaneous oxidized flavor (SOF) development. The interaction between FA and copper indicates that SOF will not develop as easily in milk with high copper content unless the substrate is available (i.e., in addition to the previously shown effect of copper in milk, unsaturated FA are required for the process of oxidation to progress). We observed a marked effect of the DGAT1 genotype on SOF development where the A allele was associated with a higher risk of SOP. Moreover, our results suggest that the effects of the FA C18:3 n-3 and of the polyunsaturated index on SOF development are beyond the effect of the DGAT1 genotype. Breed had an effect on FA composition but not on SOF development. Our results imply that copper, FA composition, and DGAT1 genotype are risk factors for SOF and considerations to these factors might be necessary in future breeding decisions.
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