New quantification method for soluble and micellar minerals in milk and application in Holstein cows

Milk has been extensively investigated as source of macro- and micro-nutrients such as essential minerals which are relevant both from technological (e.g. cheese-making) and nutritional (e.g. infant formula, fluid milk) points of view. Calcium and magnesium are essential for the stabilization of casein structure and the addition of calcium salts to milk improve milk technological traits, such as paracasein reticulum firmness. Minerals in milk can be soluble or associated to other milk components such as casein micelles and both contributes to the cheese making process. For this reason, the distinction between micellar and soluble minerals is a relevant issue in the dairy industry. Current methods for quantification of soluble and micellar minerals in milk have some limitations; for example, the rennet coagulation method needs correction factors, due to exclusion effect of major constituents, irrespective of single sample variability. The aim of this study was to develop a method for quantification of soluble and micellar minerals consistent with single sample variability. We proposed a new rennet coagulation based method, introducing a whey dilution step to exclude quantification biases from whey trapped in curd and excluded volume. The contents of Ca, Mg and K in milk, whey and diluted whey were quantified by acid digestion and inductively coupled plasma optical emission spectrometry. The repeatability of the method for micellar Ca, Mg and K was between 2.07 and 8.96%, whereas reproducibility ranged from 4.01 to 9.44%. Recovery of total milk minerals over 3 spiking levels ranged from 92 to 97%. The method has been applied to quantify micellar Ca, Mg and K to study variation of these minerals across lactation and parity in Italian Holstein cows. The results will be presented.