Gel-forming ability and radical scavenging activity of soy protein hydrolysate treated with transglutaminase

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.