Abstract: Soy glycoprotein was prepared from soy protein isolate (SPI) and glucose (m/m = 1:1) by Maillard reaction at 70, 80 or 90 ℃ for 0, 1, 2, 3, 4, 5, 6 h respectively. The reducing power, and hydroxyl radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity of products at different reaction times were determined. Moreover, browning degree, ultraviolet (UV) spectroscopic analysis, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were studied to explore the antioxidant mechanism of soy glycoprotein. The results showed that the antioxidant effect and browning degree of soy glycoprotein was significantly increased, and free amino group content was remarkably increased with an increase in reaction temperature and time. It was proved that soy glycoprotein obtained after reaction for 6 h at 90 ℃ had the maximum reducing power, which was 5.6 times higher than SPI. Soy glycoprotein obtained after reaction at 90 ℃ for 5 h exhibited the highest hydroxyl radical scavenging (a 1.69-fold increase over SPI) and DPPH radical scavenging activity (scavenging activity of 68.55%, a 3.68-fold enhancement over SPI). Through analysis of the secondary derivative ultraviolet spectrum, tryptophan migration in the protein occurred during the Maillard reaction. Meanwhile, SDS-PAGE illustrated that SPI and glucose formed high molecular weight conjugates. All in all, these results suggest that soy glycoprotein has antioxidant properties, which has a close relationship with the changes of protein structure.

Key words: soybean protein, Maillard reaction, glycoprotein, antioxidant, structure, mechanism