UNE-EN ISO 17678:2020

This document specifies a reference method for the determination of milk fat purity using gas chromatographic analysis of triglycerides. The method utiltises 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 equations based on the normalized weighted sum of individual triglyceride peaks which are sensitive to the integrity of the milk. The integrity of the milk fat may be determined by comparing the result of these equations with those previously observed for a range of pure milk fat samples. Both vegetable fats and animal fats such as beef tallow and lard can be detected.

Basically, the method applies 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.

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 whose diet contained a particularly high proportion of vegetable oils such as rapeseed, cotton or palm oil etc.;

d) obtained from cows suffering from considerable underfeeding (strong energy deficit);

e) obtained from colostrum;

f) subject 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 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 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, whose approximate content ranges from 3,1 % mass fraction to 3,8 % 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 (see Reference [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 being 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 may cause false positive results, what can be substantiated by a content of conjugated linoleic acid (C18:2 c9t11) of e" 1,3 % mass fraction (see references[16] and[17]). Nevertheless, results complying with the criteria of milk fat purity specified in this standard are accepted, even if samples were undoubtedly produced under conditions reported in this note, including those described in h).