Pre-deamidation of soy protein isolate exerts impacts on transglutaminase-induced glucosamine glycation and cross-linking as well as properties of the products

BACKGROUND Transglutaminase (TGase) induces protein glycation and cross-linking, but results in lower solubility and digestibility due to excessive cross-linking. Deamidation of soy protein isolate (SPI) by HCl converts glutamine residues, and provides less opportunity for the two reactions. Two deamidated SPI products (DSPI1 and DSPI2) were thus glucosamine-glycated and cross-linked, to clarify the effects of pre-deamidation on the two reactions and properties of the products. RESULTS DSPI1 and DSPI2 had respective degrees of deamidation of 12.2% and 27.4%. They and SPI were used to generate three glycated and cross-linked products (GC-DSPI1, GC-DSPI2 and GC-SPI) containing glucosamine of 12.0, 4.4 and 19.7 g kg −1 protein, respectively, which were reflected in their infrared spectra at two regions. These three (especially GC-SPI) had higher water-binding than SPI (8.2–12.6 versus 6.2 g g −1 protein). GC-DSPI1 and GC-DSPI2 showed better enzymatic digestion than GC-SPI. Thermogravimetric and circular dichroism analyses verified that GC-DSPI1 and GC-DSPI2 had maximum degradation rates at temperatures 12–14 °C lower than GC-SPI, and possessed a more open secondary structure. CONCLUSION SPI deamidation decreases forthcoming glycation and cross-linking, and gives the products higher digestibility, less increased hydration, lower thermal stability, and a more open secondary structure. Pre-deamidation is applicable to control the properties of GC-proteins. © 2015 Society of Chemical Industry