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首页> 外文期刊>Analytical and Bioanalytical Chemistry >Differentiation of organically and conventionally produced milk by stable isotope and fatty acid analysis
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Differentiation of organically and conventionally produced milk by stable isotope and fatty acid analysis

机译：通过稳定的同位素和脂肪酸分析区分有机牛奶和常规牛奶

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Increasing sales of organic milk mean intensified tests for authenticity are required. In addition to comprehensive documentation, analytical methods to identify organic milk, and thus to differentiate it from conventional milk, are needed for consumer protection. Because the composition of milk is fundamentally dependent on the feeding of the cows, thirty-five samples from both production systems in Germany, including farm and retail milk, were collected within 12 months, to reflect seasonal variation, and appropriate properties were analysed. Fatty acid analysis enabled organic and conventional milk to be completely distinguished, because of the higher α-linolenic acid (C18:3ω3) and eicosapentaenoic acid (C20:5ω3) content of the former. Organic milk fat contained at least 0.56% C18:3ω3 whereas the maximum in conventional milk was 0.53%. Because of the parallel seasonal course of the C18:3ω3 content of organic and conventional retail samples, however, time-resolved comparison at the five sampling dates resulted in a clearer difference of 0.34 ± 0.06% on average. Analysis of stable carbon isotopes (δ13C) also enabled complete distinction of both types of milk; this can be explained by the different amounts of maize in the feed. For conventional milk fat δ13C values were ?26.6‰ or higher whereas for organic milk fat values were always lower, with a maximum of ?28.0‰. The time-resolved average difference was 4.5 ± 1.0‰. A strong negative correlation (r = ?0.92) was found between C18:3ω3 and δ13C. Analysis of a larger number of samples is required to check the preliminary variation ranges obtained in this pilot study and, probably, to adjust the limits. Stable isotopes of nitrogen (δ15N) or sulfur (δ34S) did not enable assignment of the origin of the milk; in cases of ambiguity, however, some trends observed might be useful in combination with other properties.
机译：有机奶销量的增加意味着需要加强真实性测试。除了全面的文档记录，还需要用于识别有机牛奶，从而将其与常规牛奶区分开的分析方法，以保护消费者。由于牛奶的成分基本取决于奶牛的喂养，因此在12个月内收集了来自德国两个生产系统（包括农场和零售牛奶）的35个样品，以反映季节变化，并分析了适当的特性。脂肪酸分析可以使有机牛奶和常规牛奶完全区分开，因为前者的α-亚麻酸（C18：3ω3）和二十碳五烯酸（C20：5ω3）含量较高。有机乳脂至少包含0.56％的C18：3ω3，而常规乳中的最大值为0.53％。由于有机样品和常规零售样品中C18：3ω3含量的季节性平行变化，因此，在五个采样日的时间分辨比较得出的平均差异明显为0.34±0.06％。对稳定碳同位素（δ13 C）的分析还可以完全区分两种类型的牛奶。饲料中玉米的含量不同可以解释这一点。传统乳脂的δ13C值等于或大于26.6‰，而有机乳脂的δ13C值总是较低，最大值为28.0‰。时间分辨的平均差为4.5±1.0‰。 C18：3ω3与δ13 C之间存在很强的负相关（r = 0.92）。需要分析大量样本，以检查在该初步研究中获得的初步变化范围，并可能调整限值。氮（δ15 N）或硫（δ34 S）的稳定同位素无法确定牛奶的来源；但是，在模棱两可的情况下，观察到的某些趋势可能与其他属性结合使用。

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