Acid skim milk gels: The gelation process as affected by preheating pH

Abstract

The effect of preheating milk (10 min 80 °C) at pH values from 6.20 to 6.90 on formation of acid skim milk gels was studied by dynamic oscillation measurements. Up to pH 6.65 a higher pH of heating (pH heating) resulted in a higher G′. Since below pH 4.9 the development of G′(pH)/ G′(pH=4.9) and tan δ (pH) was similar we assume that the rearrangement processes happening below pH 4.9 were similar for all pH heating values studied. Based on data for tan δ, G′(pH) and the pH of gel formation, it was hypothesized that the differences in moduli with pH heating stem from differences in the aggregation and rearrangement processes occurring before and just after gelation (pH>4.9). These differences are partly due to greater involvement of S–S interactions at higher pH heating. Furthermore, the soluble whey protein aggregates formed during preheating are in part not incorporated in the network, the extent depending on pH.