Gelation mechanism and physical properties of glucono-δ-lactone induced alginate sodium/casein composite gels

Designing composite food gels with polysaccharide-protein mixtures as building materials has recently attracted increasing attention in the food industry. By this way, it is feasible to produce the composite gels with hierarchical microstructures and desired physical properties. In this study, we fabricated a class of glucono-8-lactone (GDL)-induced composite gels with a fixed casein concentration (8.0%, w/v) and varying alginate addition amounts (Alg, 0?1.0%, w/v). As the Alg concentration increased, the gel hardness was initially increased, but followed by a decreasing trend, which was corresponding to the structural transition of the composite gels. At low Alg concentrations (e.g., 0.1% Alg), the composite gel featured casein-dominant network; with increasing Alg addition (e.g., 0.2?0.5%), the caseins acted as the continuous gelling phase and the Alg served as the dispersed phase. When the Alg concentration was further increased (e.g., 0.75?1.0%), a bicontinuous phase structure was observed. In addition, it was found that with increasing Alg addition, the gel-setting time (Tgel) was monotonously decreased. Despite this, however, the structural evolution of the gels was still observed even after reaching the gelation point, which was dominantly ascribed to the electrostatic attraction between the two polymers that occurred at a pH range below the isoelectric point (pI) of the caseins. Overall, the composite Alg/ casein systems may emerge as a promising template for designing novel gel-related foods.