Formation and physical properties of skimmed milk/low-acyl gellan gum double gels: Influence of gelation sequence

Abstract

Low-acyl gellan gum (LA) is a typical cold- and Ca²⁺-set gelation polysaccharide and is widely used to improve the stability of yoghurt. Acid and endogenous calcium can induce the formation of skimmed milk (SM)/LA double gels. However, the effect of acidification temperature on the formation and physical properties of SM/LA double gels has not been elucidated. In this study, temperature above and below the LA transition temperature (38 °C) were used as acidification temperatures, which adjusted the gelation sequence of SM and LA. The LA gel prior to the SM gel formed at acidification temperature of 37 °C, exhibiting the highest WHC and G′ among all samples. Moreover, SM/LA-37 double gels showed two networks: one was a porous network and the other was a dense network. By contrast, SM/LA mixtures acidified at 42 °C formed double networks during the cooling stage, and the previously formed SM gel hindered the formation of the LA gel. Consequently, SM/LA-42 double gels showed lower WHC and G′ compared with SM/LA-37 double gels. Overall, gelation sequence substantially affected the physical properties of SM/LA double gels. Our findings provide basis for adopting optimal methods to improve yoghurt quality and revealing the gelation mechanism involved in SM/LA double gels.