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