Transglutaminase-induced cross-linking and glucosamine conjugation of casein and some functional properties of the modified product

In the presence of glucosamine, a microbial transglutaminase was used as a biocatalyst to cross-link bovine casein and incorporate a glucosamine moiety into casein. SDS-PAGE analysis indicated that cross-linking and glucosamine conjugation occurred simultaneously. A modified casein product with a glucosamine conjugation of about 1.15 mol mol−1 casein, measured by HPLC, was prepared when casein (3%, w/v) was incubated at 37 °C and pH 7.5 with transglutaminase added at 10 kU kg−1 casein and glucosamine added at molar ratio of 3:1 (glucosamine acceptor to acyl donor in casein) for 4 h. The evaluation results demonstrated that the modified product showed improved solubility, lower surface hydrophobicity, better emulsifying and foaming properties, higher apparent viscosity and more intense viscoelastic character compared with the original casein or cross-linked casein. This modification technique might also be applied to improve some functional properties of other food proteins.