ISO 8968-1 |IDF 20-1:2014规定了一种根据凯氏原理，使用传统消化法和分段消化法测定牛奶和奶制品中氮含量和粗蛋白质含量的方法。本方法适用于:液态牛奶（全脂、部分脱脂或脱脂牛奶）、山羊和绵羊全脂牛奶；硬奶酪、半硬奶酪和加工奶酪；奶粉和奶粉制品（包括乳基婴儿配方奶粉、乳蛋白浓缩物、乳清蛋白浓缩物、酪蛋白和酪蛋白酸盐）。 这些方法不适用于含有酪蛋白酸铵的样品。

ISO 8968-1|IDF 20-1:2014 specifies a method for the determination of the nitrogen content and crude protein calculation of milk and milk products by the Kjeldahl principle, using traditional and block digestion methods. The methods are applicable to: liquid cow's (whole, partially skimmed or skimmed milk), goat's and sheep's whole milk; hard, semi-hard and processed cheese; dried milk and dried milk products (including milk-based infant formulae, milk protein concentrate, whey protein concentrate, casein and caseinate). The methods are not applicable to samples containing ammonium caseinate.