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

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 degrees 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 degrees 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 degrees 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.