Effects of pH, calcium-complexing agents and milk solids concentration on formation of soluble protein aggregates in heated reconstituted skim milk

The proportion of protein present in the supernatant after centrifugation and the formation of soluble protein aggregates in heated (90 degrees C for 10 min) reconstituted skim milk were investigated as a function of (a) pH, (b) milk concentration 9-21 , w/w (milk solids non-fat, MSNF) and (c) addition of calcium-complexing agents (orthophosphate or EDTA). Compositional changes in milk, resulting from pH adjustment or salt addition, altered the distribution of caseins between the serum and micellar phases of milk prior to heating, and influenced the amount and composition of soluble aggregates formed during heat treatment. Although milk pH was a good predictor of the aggregation behaviour of the proteins during heating of milk of different solids concentrations, neither the proportion of protein in the supernatant prior to heating nor the pH alone could predict the aggregation behaviour when the composition was adjusted with mineral salts.