Structural characteristics of gluconic acid δ-lactone induced casein gels as regulated by gellan gum incorporation

Abstract The co-gelation phenomenon of caseins and gellan in yogurt-related products is usually observed, highlighting the possibility of developing mixed casein/gellan systems as a new type of food gels. In this study, mixed gellan/casein gels were prepared by adding different amounts of gluconic acid δ-lactone (GDL) to acidify gellan/casein mixtures at a fixed casein concentration (8.0%, w/v) and varying gellan concentrations (0-0.6%, w/v). It was found that both the gellan concentration and the GDL addition amount affected the gel microstructures and gel strength; with increasing gellan concentration, the mixed systems gradually exhibited a significant phase separation, accompanied by a structural transition from homogeneous, casein-dominant gel structure to a “water-in-water” emulsion structure (where the casein-enriched phase acted as the continuous phase and the gellan-enriched phase as the dispersed phase). A higher level of GDL addition slightly retarded but did not abolish the phase separation by inducing a quicker gelation process. Moreover, based on the prepared gel matrices, composite gellan/casein emulsion gels were successfully developed. Conclusively, our results indicate that gellan can be used to regulate the microstructures of casein-based gels, which may further pinpoint the possibility of using mixed gellan/casein systems to diversify food gel design strategies.