ISO 17678|IDF 202:2010 specifies a reference method for the determination of milk fat purity using gas chromatographic analysis of triglycerides. Both vegetable fats and animal fats such as beef tallow and lard can be detected. By using defined triglyceride equations, the integrity of milk fat is determined.
Basically, the method applies to bulk milk, or products made thereof, irrespective of feeding, 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.
However, under the circumstances listed hereafter, a false positive result can be obtained. Hence, the method is not applicable to milk fat: a) obtained from bovine milk other than cow's milk; b) obtained from single cows; c) obtained from cows which received an exceptionally high feeding of pure vegetable oils such as rapeseed oil; d) obtained from colostrum; e) subjected to technological treatment such as removal of cholesterol or fractionation; f) obtained from skim milk or buttermilk; g) extracted by 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 g), substantial quantities of partial glycerides or phospholipids can pass into the fat phase. Consequently, the scope of ISO 17678|IDF 202:2010 excludes certain products and particularly cheese, whose ripening process can also affect the fat composition to such a degree that a false positive result is obtained.