Improvement of calcium sulfate-induced gelation of soy protein via incorporation of soy oil before and after thermal denaturation

Soy protein-based foods have attracted extensive attention for their potential health benefits. In this study, soy protein isolate (SPI) emulsions containing 10-70 mL/L of soy oil were primarily prepared either by adding the oil, emulsifying and heat treatment (OEH), or by heat treatment of the soy protein dispersion, addition of oil and emulsification (HOE). After adding CaSO4, the rheological properties of emulsions during gelation and the textural properties of the resulting gels were investigated and compared. The results showed that the increase in the volume fraction (Phi) of the soy oil from 10 to 70 mL/L resulted in the increase of the final elastic modulus (G') of HOE and OEH emulsion gels from 5216.7 to 5827.3 Pa, and 4184.3-4935.3 Pa, respectively. The gel hardness and water-holding capacity gradually improved with increasing Phi. HOE gels exhibited greater performance of gelling properties than OEH gels at the same Phi. Confocal laser scanning microscopy images demonstrated that HOE gels, with smaller soy oil droplets dispersed within the networks, had more homogeneous and compact network structures than OEH gels. Reinforced emulsifying capacity of denatured SPI could enhance the protein-oil interactions and result in improvement of CaSO4-gelation of SPI.