Department of Safety and Quality of Milk and Fish Products, Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Hermann-Weigmann-Str. 1, 24103, Kiel, Germany.
Anal Bioanal Chem. 2010 Oct;398(3):1493-500. doi: 10.1007/s00216-010-3995-y. Epub 2010 Jul 25.
Analysis of the stable isotope ratio of carbon (delta (13)C) and alpha-linolenic acid (C18:3omega3) content in milk fat is a useful indicator of organic milk production. Referring to corresponding measurements, further analyses of stable isotope ratios were performed in 120 samples of conventionally and organically produced whole milk collected from German retailers during a period of 18 months. Conventional milk predominantly exhibited higher delta (15)N values than organic milk, the latter of which never exceeded a maximum delta (15)N threshold value of 5.50 per thousand. Measurements of delta (34)S did not differ significantly between organic and conventional milk. Because delta (13)C, in general, is related to maize consumption, delta (13)C in milk protein and delta (13)C in milk fat were equally suited for authentication of organic milk. Thus, a high correlation (r = 0.99) was established between delta (13)C in milk protein and lipids. Although occurring on different levels in organic and conventional milk, the relatively constant fractionation of carbon isotopes between protein and fat will allow for the advanced detection of adulteration in processed milk products, such as fraudulent combinations of organic milk fat and conventional skim milk. In addition to the strong correlation between C18:3omega3 and delta (13)C(protein) (r = -0.91), a mutual dependence was identified between both delta (13)C(protein) and delta (15)N (r = 0.66) and C18:3omega3 and delta (15)N (r = -0.61). Thus, multi-variable analyses are useful to increase robustness and reduce the number of exceptions in organic milk authentication. Future work involving multivariate statistical analysis can possibly further improve milk authentication in various respects including differentiating between brands of retail milk.
分析牛奶脂肪中的稳定碳同位素比值（δ（13）C）和α-亚麻酸（C18:3ω3）含量是有机牛奶生产的有用指标。参考相应的测量结果，在 18 个月的时间里，从德国零售商处采集了 120 份常规和有机生产的全脂牛奶样本，对其稳定同位素比值进行了进一步分析。常规牛奶的δ（15）N 值普遍高于有机牛奶，后者的δ（15）N 值从未超过 5.50‰的最大值。有机牛奶和常规牛奶的δ（34）S 测量值没有显著差异。由于δ（13）C 通常与玉米的消耗有关，因此牛奶蛋白中的δ（13）C 和牛奶脂肪中的δ（13）C 同样适用于有机牛奶的认证。因此，牛奶蛋白和脂肪中的δ（13）C 之间建立了高度相关（r = 0.99）。尽管有机牛奶和常规牛奶中的δ（13）C 存在差异，但蛋白质和脂肪之间碳同位素的相对恒定分馏将允许对加工乳制品（如有机牛奶脂肪和常规脱脂牛奶的欺诈性组合）中的掺假进行高级检测。除了 C18:3ω3 和δ（13）C（protein）之间的强相关性（r = -0.91）外，还确定了两者之间的相互依赖关系，即δ（13）C（protein）和δ（15）N（r = 0.66）之间以及 C18:3ω3 和δ（15）N（r = -0.61）之间。因此，多元分析可用于提高有机牛奶认证的稳健性并减少异常值的数量。涉及多元统计分析的未来工作可能会在各个方面进一步改善牛奶认证，包括区分零售牛奶的品牌。
