Dry-heat treatment of skim milk powder improves acid-induced gelation due to protein glycation and cross-linking of caseins

Abstract

Dry-heat-treated sodium caseinate improves yogurt curd strength, but its production is time-consuming. Thus, a simpler pretreatment is needed. We conducted this study to investigate the effects of dry-heat treatment (65 °C, RH 8 %, 2–6 days) of skim milk powder on acid-induced gelation and identify improvement factors. Acid-induced gels were formed by the addition of 1.84 % (w/v) glucono-δ-lactone to skim milk powder dispersions (protein conc., 40 mg/mL). Gel strength improved proportionally to dry-heat treatment duration. We examined the relationship between the improvement of curd strength and protein denaturation induced upon heat treatment of skim milk powder. We observed improved curd strength due to a decrease in zeta potential and an increase in the surface hydrophobicity of casein micelles as well as cross-linking of caseins, which were a result of Maillard reactions. These results suggest that dry-heat treatment of skim milk powder is useful for yogurt manufacturing.