Food adulteration

Fat is where not only the flavour is: detection of non-milk fat in milk by GC and LDA

What you taste is not always what you get. Unless, of course, your tongue is either very well-trained, or capable of linear discriminant analysis (LDA). Researchers in Mexico have now optimised the evaluation of non-milk fats in dairy products using GC detection of triacylglycerol profiles in conjunction with LDA.

Milk is defined by the International Dairy Federation as the "product of the normal secretion of the udder, obtained by one or several milkings, with no addition or subtraction." Additional national legislation in various countries further stipulates that milk must contain only its own fat. As such, the addition of non-milk fat (NMF) to milk and milk derivatives must be indicated on the label. If not, the milk product is considered to be adulterated.

Scientists at the Universidad Autónoma Metropolitana Unidad Xochimilco in Mexico have recently reported an improved method for the detection of non-milk fat in milk using gas chromatography determination of triacylglycerol profiles coupled with linear discriminant analysis. Published in the Journal of Dairy Science, their paper describes the development of the method and its application to the analysis of raw milk and ultrapasteurised milk fat from three commercial sources, in comparison with profiles obtained from pork lard, bovine tallow, fish oil, peanut, corn, olive, and soy. Raw milk fat samples were adulterated with non-milk fats at levels ranging from 5% to 20%. Linear discriminant analysis allowed the correct detection of over 94% of the samples having less than 10% non-milk fats. Using this discriminant function, the triacylglycerol profiles of the ultrapasteurised milk fats were analysed, indicating that one commercial source added non-milk to its product.

Article by R. Gutiérrez et al. on non-milk fat detection by GC and LDA, Journal of Dairy Science, May 2009

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