Physicochemical properties of soybean protein isolate affected by the cross-linking with horseradish peroxidase, glucose oxidase and glucose

Abstract

Horseradish peroxidase (HRP), glucose oxidase, and glucose were used at 37 °C to cross-link soybean protein isolate (SPI) by one- and two-step treatments, via inducing dityrosine formation in the molecules of SPI. HRP, glucose oxidase, and glucose were added at 200, 4 U, and 0.1 mmol per gram protein, respectively, whilst a total reaction time of 3 h was used. In comparison with SPI, two cross-linked SPI products thus prepared showed similar oil absorption capacity (P > 0.05), slightly higher surface hydrophobicity (about 5−11%), but 14−30% decreases in solubility at pH values of 4.5, 7.0 and 9.0 (P < 0.05). Two cross-linked SPI products also demonstrated enhanced emulsion stability indices (about 26−71%) but decreased emulsifying activity indices (about 8−12%) than SPI (P < 0.05), especially one-step treatment was used to cross-link SPI. In general, aqueous dispersions of the two cross-linked SPI products (especially that prepared through one-step treatment) had higher values in apparent viscosity, elastic and viscous moduli than the counterpart dispersion of SPI. It is concluded that HRP, glucose oxidase, and glucose can be applied efficiently to modify several physicochemical properties (especially rheological and emulsifying properties) of SPI.