Heat-induced gels from pea protein soluble colloidal aggregates: Effect of calcium addition or pH adjustment on gelation behavior and rheological properties

Heat-induced protein gels are appreciated due to their texture in a variety of food products. To support the shift to more sustainable protein consumption more knowledge is needed about plant protein gelation behavior and rheological properties of gels. In this study, the effect of calcium concentration (10 mM-100 mM) and pH (5.9-6.8) on heat-induced gelation behavior of 10 w/w% pea protein water-soluble extract separated from a commercial pea protein isolate (WSE-PPI) were for the first time investigated and compared. The rheological results show G' values of around 3000 Pa for gels containing 20 mM calcium, and then a decrease in G' by a factor similar to 1.3 when the calcium concentration increased to 100 mM, whereas a continuous increase in gel strength was observed with the pH decrease of WSE-PPI dispersions. By comparison of calcium-addition and pH-adjusted heat-induced gels at the same pH, it was found that at low calcium concentrations (<= 20 mM), the calcium-assisted gels exhibited higher gel strength. Contrariwise, at high calcium concentrations (>= 50 mM), the pH-adjusted gels have higher gel stiffness and larger deformability before rupture. CLSM results verified this finding and show that the gel structure of pH-adjusted gels are more homogenous, containing significantly more compact structure. Overall, our findings show a systematic link between microstructure and rheological properties of heat-induced gels, which can be controlled by the calcium addition and pH adjustment. These results provide valuable information for the modulation, design, and customization of plant derived protein gels for specific food applications.