Development of aqueous and emulsion hydrogel (bigel) formulations based on soy protein isolate, tragacanth gum, carboxymethyl cellulose, and corn oil as potential oil fat mimics in food products: A biopolymer-based approach

• Bigels based on soy protein isolate/corn oil (SPI/CO) containing tragacanth (TG) and carboxymethyl cellulose (CMC) was prepared. • Good compatibility was observed between bigel composite components. • Produce bigel had a zeta potential of -49 mV, which indicated the very good stability of the produced bigel. • Optimum bigel has a good ability to replace solid fat in food formulation. In this research, the process of making aqueous and emulsion hydrogel (bigel) based on soy protein isolate (SPI), tragacanth gum (TG), carboxymethyl cellulose (CMC), and corn oil (CO) was studied. The physicochemical and structural properties of the prepared hydrogels were investigated, and the best hydrogel formulation was selected in terms of textural and physical characteristics. Central composite design was used to investigate the effect of CO, TG, and CMC. The obtained results showed that CO and TG decreased the pH, and CMC increased the pH. Corn oil decreased overall electrical conductivity, and both TG and CMC increased electrical conductivity. Moisture content and swelling rate of the hydrogels decreased by incorporation of CO. While TG and CMC did not have a significant effect on the moisture content or swelling percentage. CO greatly reduced the amount of syneresis. According to the lightness (L*) values, CO increased the lightness significantly. By incorporation of CO, the adhesion of hydrogel decreased, but TG and CMC increased the adhesion strongly. According to the results, the emulsion hydrogel containing SPI, TG, CMC, and CO had a zeta potential of -49 mV, which indicated the very good stability of the produced emulsion hydrogel. Examination of SEM images showed that the produced composite hydrogel has a coherent and somewhat uniform structure. Physical connections and electrostatic interactions between composite components were confirmed by comparing FTIR spectra. In the optimal conditions obtained through the desirability function, the amount of CO was 13.2 %, 0.1% of TG, and 1.32 % of CMC. The zeta potential in the optimal conditions was -33.94 mV, and in this zeta potential, the produced emulsion hydrogel is completely stable.