Fatty acids routed from fresh grass to milk influence S13C in milk

摘要

Dairy production systems vary widely in their feeding and livestock-keeping regimens. Both are well-known to affect milk quality and they arc important topics for consumer perceptions. Here we examine whether carbon isotope composition (S'-'C) in milkcan be sufficiently predicted from feeding information, so that measurement of SljC in milk could serve as authenticity proof. We obtained 671 milk samples from 40 farms distributed over Central Europe to measure S13C and fatty acid composition. Feedingprotocols by the farmers in combination with a model based on S13C feed values from the literature were used to predict S13C in feed and subsequently in milk. The model considered dicrary contributions of C3 and C4 plants, contribution of concentrates,altitude of forage production, seasonal variation in 12/13CO, Suess's effect, and diet-milk fractionation. Predicted and measured S1: C in milk correlated closely (t-2=0.93). Analysing milk for 513C allowed validation of a reported C4 component with an uncertainty of <8% in 95% of all cases. This included the uncertainties of the method (measurement and prediction) and of the feeding information. However, the mismatch was not random but varied seasonally and correlated with the seasonal variation in long-chain fatty acids originating from fresh grass. This indicated routing of long-chain fatty acids from fresh grass to milk. In conclusion, S13C in milk can be predicted in the authentication case but larger errors occur with high proportions of fresh-grass feeding, due to routing of long-chained fatty acids from fresh grass to milk.