Effect of glycosylation and limited hydrolysis on structural and functional properties of soybean protein isolate

The effects of glycosylation followed by limited hydrolysis on the structural and functional properties of soybean protein isolate (SPI) were investigated. SPI was glycosylated by transglutaminase (TGase) in the presence of oligochitosan to generate a glycosylated soybean protein isolate (GSPI) and then hydrolyzed using Alcalase to obtain hydrolysates with degree of hydrolysis (DH) of 1%, 2% and 4%. Structural properties were characterized using estimate of molecular weight distribution and circular dichroism (CD) spectra. Electrophoresis analysis revealed that GSPI contains peptide polymers, and its hydrolysates exhibit broad molecular weight distributions. CD analysis indicated more flexible structure for GSPI compared to SPI, and the following limited hydrolysis of GSPI induces even more flexible structure on its hydrolysates. GSPI showed significant increase in the apparent viscosity at the shear rate of 0.1-10/s. Emulsion stability of GSPI also increased by 33.9% than that of SPI. Hydrolysates from GSPI, especially for DH of 4%, showed significantly improved emulsifying activity index, increasing by 39.2% compared to SPI. The hydrolysates also showed notably enhanced antioxidant activities, namely, DPPH radical-scavenging ability and reducing power. These results revealed that TGase-induced glycosylation and further limited hydrolysis may have potential for creating food ingredients with improved functional properties.