A comparison of the acid gelation properties of nonfat cow, sheep, and goat milk with standardized protein contents

Abstract

Skimmed cow, sheep, and goat milks were adjusted to the same total protein and dry matter level, heat treated and glucono delta lactone (GDL) was added for slow acidification. Acid coagulation was monitored by measuring the turbidity and viscosity every 10 min and pH was measured every min throughout the incubation. Physicochemical composition (total solids, fat, protein, casein, bound and soluble Ca, P, Fe, Mg, K, Na), pH, acidity, SDS-PAGE analysis of the milk samples and viscosity, serum separation, and SEM images of the acidified milk gels were determined. During incubation, the highest decrease in pH was observed with cow milk, while sheep milk pH was higher and was above pH 4.6 at the end of incubation. Cow milk gels had the highest viscosity, lowest serum separation, and more homogenous microstructure. Sheep milk gels had a lower viscosity than cow milk and goat milk formed the weakest acid gels of all. Novelty impact statement Acid gelation of the milk is essential for the production of many dairy products that involve fermentation such as yogurt. Previous studies showed major differences between cow, sheep, and goat milk yogurts; however, there is not much study that compares acid gelation and gel properties of standardized cow, sheep, and goat milks. We found significant differences between acid gelation and gel properties of cow, sheep, and goat milks even if their total protein, total solids, and fat contents were adjusted to the same level; thus our findings highlight the importance of the differences in type and ratio of the protein fractions.