Transglutaminase-induced cross-linking and glucosamine conjugation in soybean protein isolates and its impacts on some functional properties of the products

In the presented work, we exploited microbial transglutaminase as a biocatalyst and glucosamine as an acyl acceptor to modify soybean protein isolates (SPI) by cross-linking and glucosamine conjugation and evaluated some functional properties of the modified product prepared. Electrophoretic studies revealed that transglutaminase-induced cross-linking and glucosamine conjugation occurred simultaneously during modification reaction, and some polymers of glycoproteins with higher molecular weights were formed in the modified product. HPLC analysis demonstrated that about 3.3 mol of glucosamine could be conjugated to 1 mol of SPI, under the preparation conditions as following: SPI concentration of 3% (w/v), acyl donor in SPI/glucosamine acceptor molar ratio of 1:3, transglutaminase addition level of 10 U g−1 proteins, reaction temperature of 37 °C, and reaction time of 6 h. Compared to SPI and transglutaminase-induced cross-linked SPI, the modified product with glucosamine conjugation about 3.3 mol mol−1 SPI clearly exhibited lower surface hydrophobicity, better interfacial properties (especially in emulsion and foaming stability), markedly increased apparent viscosity in the prepared dispersion, and higher enzymatic digestibility in vitro. Our results showed that this modification technique might have the potential as an effective approach to improve the functional properties of SPI.