Physicochemical properties of skim milk gels obtained by combined bacterial fermentation and renneting: Effect of incubation temperature at constant inoculum level

Abstract

Acid-rennet skim milk gels were formed by simultaneous bacterial fermentation and renneting at three different temperatures at constant inoculum level. Temperatures >24 °C accelerated milk acidification and resulted in firmer and more cohesive gels. It was possible to shorten the acidification process from ∼795 min (28 °C) to ∼600 min (32 °C) without affecting curd quality; there was no significant difference in texture properties between curds formed at 28 or 32 °C. Internal structure of curds, observed using scanning electron microscopy, was substantially affected by acidification rate. More crosslinking and thicker bonds were formed when milk was coagulated at 32 °C compared with 24 or 28 °C. Faster network formation at 32 °C resulted in bigger pores, favouring whey leakage. Increasing temperature significantly increased syneresis, due to intensified intra-network rearrangements. Milk incubation temperature can therefore be used as a process variable to increase syneresis and alter acid-rennet gel texture.