本文件规定了使用甘油三酯的气相色谱分析测定乳脂纯度的参考方法。该方法利用乳脂的甘油三酯指纹与其他脂肪和油的单个甘油三酯指纹的差异来确定超出乳脂正常观察范围的样品。这是通过使用基于对牛奶完整性敏感的单个甘油三酯峰的归一化加权和的定义的甘油三酯公式来实现的[6][7]。乳脂的完整性可以通过将这些公式的结果与先前对一系列纯乳脂样品观察到的结果进行比较来确定[12]。植物脂肪和动物脂肪如牛油和猪油都可以检测到。 该方法适用于散装牛奶或由其制成的产品，而不考虑普通喂养实践、品种或泌乳条件的变化。特别地，该方法适用于从声称含有成分不变的纯乳脂的奶制品如黄油、奶油、牛奶和奶粉中提取的脂肪。 由于可能出现假阳性结果，因此该方法不适用于与以下情况相关的乳脂: a)得自除牛乳以外的牛乳； b)从单头奶牛获得； c)从其日粮中含有特别高比例植物油如菜籽油、棉油或棕榈油等的奶牛获得； d)从患有严重喂养不足(强烈能量缺乏)的奶牛获得； e)得自初乳； f)进行技术处理，例如去除胆固醇或分馏； g)得自脱脂乳、酪乳或乳清； h)从显示增加的脂解的干酪获得；i）使用Gerber、Weibull？伯恩特罗普还是施密德？邦津斯基？Ratzlaff方法，或使用去污剂分离的方法（例如乳品工业局方法）。 使用i)中规定的提取方法，大量的偏甘油酯或磷脂可以进入脂肪相。 注1:在自然界中，丁酸（正丁酸）（C4）仅存在于乳脂中，可以定量估计植物和动物脂肪中低至中等量的乳脂。由于C4的变化很大，其近似含量从3.1%脂肪质量分数到3.8%脂肪质量分数，很难提供高达20%质量分数的外来脂肪与纯乳脂比率的定性和定量信息[11]。 注2在实践中，不能从植物脂肪的甾醇含量得出定量结果，因为它们取决于生产和加工条件。此外，使用甾醇定性测定外来脂肪是不明确的。 注3由于特殊的喂养做法，如与c）和d）相关的做法，有时会报告来自某些亚洲地区的牛奶出现假阳性结果[15]。此外，纯草饮食，如山区，特别是高地牧场喂养，有时会导致假阳性结果，这可以通过脂肪酸质量分数≥1.3%的共轭亚油酸（C18:2 c9t11）含量来证实[16][17]。然而，符合本文件中规定的乳脂纯度标准的结果是可接受的，即使样品无疑是在本说明中报告的条件下生产的，包括h）中描述的条件。 注4如果怀疑阳性结果是由与c）或d）相关的情况引起的，可以应用另一种分析方法，如脂肪酸或甾醇分析来确认结果。由于类似或增加的限制（例如，如注释1和注释2中所述），通过另一种方法获得的阴性结果不适合对比确认乳脂纯度。

This document specifies a reference method for the determination of milk fat purity using gas chromatographic analysis of triglycerides. The method utilizes the differences in triglyceride fingerprint of milk fat from the individual triglyceride fingerprints of other fats and oils to determine samples which are outside the range normally observed for milk fat. This is achieved by using the defined triglyceride formulae based on the normalized weighted sum of individual triglyceride peaks which are sensitive to the integrity of the milk^[6][7]. The integrity of the milk fat can be determined by comparing the result of these formulae with those previously observed for a range of pure milk fat samples^[12]. Both vegetable fats and animal fats such as beef tallow and lard can be detected. The method is applicable to bulk milk, or products made thereof, irrespective of the variation in common feeding practices, breed or lactation conditions. In particular, the method is applicable to fat extracted from milk products purporting to contain pure milk fat with unchanged composition, such as butter, cream, milk and milk powder. Because a false-positive result can occur, the method does not apply to milk fat related to these circumstances: a) obtained from bovine milk other than cow's milk; b) obtained from single cows; c) obtained from cows whose diet contained a particularly high proportion of vegetable oils such as rapeseed, cotton or palm oil, etc.; d) obtained from cows suffering from serious underfeeding (strong energy deficit); e) obtained from colostrum; f) subjected to technological treatment such as removal of cholesterol or fractionation; g) obtained from skim milk, buttermilk or whey; h) obtained from cheeses showing increased lipolysis; i) extracted using the Gerber, Weibull?Berntrop or Schmid?Bondzynski?Ratzlaff methods, or that has been isolated using detergents (e.g. the Bureau of Dairy Industries method). With the extraction methods specified in i), substantial quantities of partial glycerides or phospholipids can pass into the fat phase. NOTE 1 In nature, butyric (n-butanoic) acid (C4) occurs exclusively in milk fat and enables quantitative estimations of low to moderate amounts of milk fat in vegetable and animal fats to be made. Due to the large variation of C4, for which the approximate content ranges from 3,1 % fat mass fraction to 3,8 % fat mass fraction, it is difficult to provide qualitative and quantitative information for foreign fat to pure milk fat ratios of up to 20 % mass fraction^[11]. NOTE 2 In practice, quantitative results cannot be derived from the sterol content of vegetable fats, because they depend on production and processing conditions. Furthermore, the qualitative determination of foreign fat using sterols is ambiguous. NOTE 3 Due to special feeding practices such as those related to c) and d), false-positive results have sometimes been reported for milk from certain Asian regions^[15]. Moreover, grass-only diets such as mountain and, in particular, highland pasture feeding sometimes cause false-positive results, which can be substantiated by a content of conjugated linoleic acid (C18:2 c9t11) of ≥ 1,3 % fatty acid mass fraction^[16][17]. Nevertheless, results conforming to the criteria of milk fat purity specified in this document are accepted, even if samples were undoubtedly produced under conditions reported in this note, including those described in h). NOTE 4 In cases where a positive result is suspected to be caused by circumstances related to c) or d), another analytical method, such as fatty acid or sterol analysis, can be applied to confirm the finding. Due to similar or increased limitations (e.g. as described in NOTE 1 and NOTE 2), a negative result obtained by another method is not appropriate to contrastingly confirm milk fat purity.