Molkentin Joachim
Department of Safety and Quality of Milk and Fish Products, Max Rubner Institute, Federal Research Institute of Nutrition and Food, Hermann-Kiel, Germany.
J Agric Food Chem. 2009 Feb 11;57(3):785-90. doi: 10.1021/jf8022029.
The carbon stable isotope ratio (delta(13)C) and the alpha-linolenic acid (C18:3omega3) content of milk fat were analyzed to examine their applicability as general markers for the authentication of organic retail milk in Germany. To record the variable effect of feeding, including the seasonal influence on milk composition, three conventionally and three organically produced brands of retail milk were collected biweekly during a period of 18 months. Altogether 286 milk samples were analyzed. Threshold values for the identification of German organic milk were established and allowed to delimit almost all conventional samples. Organic retail milk was always above a minimum C18:3omega3 content of 0.50% and below a maximum delta(13)C of -26.5 per thousand. The universal and strongly negative correlation (r = -0.93) between C18:3omega3 and delta(13)C impedes the intentional manipulation of conventional milk. Conventional milk can naturally exceed the C18:3omega3 limit under atypical and rare conditions, but differentiation from organic milk can be improved by time-resolved comparison of data. In contrast with the general opinion, organic milk did not generally contain more c9,t11-C18:2 (CLA) than conventional milk. The proposed limits may deviate with dairy products containing milk from foreign countries.
分析了乳脂肪的碳稳定同位素比率（δ¹³C）和α-亚麻酸（C18:3ω3）含量，以检验它们作为德国有机零售牛奶认证通用标志物的适用性。为记录饲养的可变影响，包括季节对牛奶成分的影响，在18个月期间每两周收集三个传统生产和三个有机生产的零售牛奶品牌。共分析了286个牛奶样本。确定了德国有机牛奶的识别阈值，几乎可以界定所有传统样本。有机零售牛奶的C18:3ω3含量始终高于0.50%的最低值，δ¹³C低于-26.5‰的最高值。C18:3ω3和δ¹³C之间普遍且强烈的负相关（r = -0.93）阻碍了对传统牛奶的蓄意操纵。在非典型和罕见条件下，传统牛奶自然可能超过C18:3ω3限值，但通过对数据进行时间分辨比较可以改善与有机牛奶的区分。与普遍观点相反，有机牛奶通常并不比传统牛奶含有更多的c9,t11-C18:2（共轭亚油酸）。对于含有外国牛奶的乳制品，建议的限值可能会有所不同。
