Enzymatic and fluorometric determination of triacylglycerols in cow milk and other opaque matrices

The fat content of milk is an important indication of quality, both economically and physiologically. Existing analytical methods of milk fat are based on physical determination, i.e. gravimetric determination or near infrared spectroscopy (IR). Triacylglycerols (TAG) constitute up to 98% of total fat in milk. The present study describes a new method for determination of triacylglycerols in milk. The present method is a chemical, i.e. enzymatic–fluorometric assessment of glycerol, the content of TAG is consequently given in mol per litre. The method demonstrates a good accuracy and precision and the correlation with standard IR methods shows a fine association between the different assessment methods (n = 228; r = 0.905). Fatty acid profiles of sixty individual milk samples indicate that parameters co-linearly connected to specific fatty acids may explain a considerable amount of the variation between the methods. Furthermore, discrepancies between the present method and the established IR method may partly be due to the fact that IR spectroscopy is calibrated individually against gravimetric methods not taking fatty acid profiles and thereby molar weight of TAG into account.