Altering the physico-chemical and processing characteristics of high heat-treated skim milk by increasing the pH prior to heating and restoring after heating

Abstract

Skim milk was pH-adjusted from 6.6 to 7.5, high heat treated (HHT, 95 °C × 2 min) or held unheated for 1 h, re-adjusted to pH 6.6, and analysed. HHT at pH 6.6 resulted in denaturation of ∼ 67% of total whey protein, partial association of denatured whey protein with the casein micelle, an increase in casein micelle size, and reductions in concentrations of serum casein, Ca and P. These changes were paralleled by a marked deterioration in rennet coagulability, higher ethanol stability in the pH range of 6.2-6.6 (P < .05), and a reduction in the pH of maximum heat coagulation time (HCT) (P < .05). Increasing the pH before heat treatment led to increases in casein dissociation and the concentrations of κ-casein and denatured whey protein in the serum, and a reduction in casein micelle size (P < .05). Simultaneously, HCT at pH 6.6-6.7 and 7.2 increased significantly.

Keywords: Biochemical changes; Ethanol stability; Heat stability; High heat treatment; PH at heating; Rennet gelation; Skim milk.