Calcium and phosphorus equilibria during acidification of skim milk at elevated temperature

The solubilisation of calcium and phosphorus from casein micelles was studied during skim milk acidification with glucono-delta-lactone. Dynamic measurements of storage modulus (G') as a function of time were recorded during the formation of acid milk gels with a final pH of 4.6. An abnormal change in slope of G' (G'(shoulder)) as a function of time was observed at 50 and 60 degrees C with decreasing pH. During the appearance of G'(shoulder) immediately after onset of gelation there was a large change in the concentrations of serum and micellar calcium and phosphorus for change of 0.1 pH units. The onset of gelation at pH values, where the colloidal calcium phosphate is not fully solubilised, is coupled to casein micelle disintegration, and will create increased bonding between caseins forming the final acid gel with a concomitant and sudden solubilisation of calcium and phosphorus from the casein micelles. (C) 2015 Elsevier Ltd. All rights reserved.