Structure formation in yogurt: rheology and microstructure

摘要

Skim milk was subjected to various intensities of heating and subsequently inoculated with a commercial yogurt starter culture. The microstructure and rheological properties of the resulting acid milk gel was investigated. A scenario for structure formation in heat-treated milk is proposed based on association of whey protein to the micelle and resulting formation of an initial, whey protein facilitated network. A decrease in pH at gelation was observed with increased intensity of heat-treatment, and heat-treatment in excess of 70oC/5 min resulted in a network consisting of thinner, but more interconnected protein strands and having higher gel strength than gels formed at lower heat-treatment of milk. No difference was found in the present study between heat-treatments of 80oC/5 min, 80oC/30 min or 90oC/5 min, presumably due to the effect of whey protein association to the casein micelles being limited by a finite number of binding sites.