Gel-forming Ability and Radical-scavenging Activity of Soy Protein Hydrolysate Treated with Transglutaminase

ABSTRACT: Gel-forming ability and 1,1-diphenyl-2-picrydrazyl (DPPH) radical-scavenging activity of the peptic hydrolysate from soy protein isolate (SPI) were investigated. The gel-forming ability of mixtures consisted of SPI and its hydrolysate decreased as the percentage of hydrolysate increased. The inferior gel-forming ability of the hydrolysate was shown to be related to both the low surface hydrophobicity of the hydrolysate and the drop in sulfhydryl exchange reactions during gelation. Although antioxidants in the SPI-hydrolysate mixture (SHM) could be helpful in enhancing the radical-scavenging activity of the peptide-based gel, they suppressed the oxidization of sulfhydryls in sulfhydryl group/disulfide bond interaction. As a result of this, antioxidants present reduced the gel-forming ability of the SHM. The addition of transglutaminase (TGase) improved the gel-forming ability of SHM. A mixture of 70% SPI and 30% hydrolysate in the presence of TGase resulted in a gel with good gelling property and high radical-scavenging activity.