Effects of caseinate deamidation on transglutaminase-induced glucosamine conjugation and cross-linking as well as properties of the treated caseinates

Caseinate was treated by diluted HCl solution to achieve degrees of deamidation of 16.6% and 28.1%, which resulted in lower surface hydrophobicity. Two deamidated caseinates were treated by transglutaminase and glucosamine to carry out glucosamine conjugation and cross-linking, to generate two modified caseinates (glucosamine-conjugated and cross-linked deamidated caseinates). Two modified caseinates contained less glucosamine (6.9–9.8 versus 12.6 g/kg protein) and higher reactable –NH2 (0.54–0.56 versus 0.51 mol/kg protein) than the glucosamine-conjugated and cross-linked caseinate, declaring they were less glycated and less cross-linked than caseinate. Two modified caseinates had better solubility in pH 3.0–9.0, higher water- and oil-binding and emulsion stability but lower emulsifying activity than caseinate; however, they also exhibited better solubility and emulsifying activity than the counterpart. It is thus concluded that HCl-induced deamidation was powerful enough to control transglutaminase-induced glucosamine conjugation and cross-linking as well as functional properties of the treated caseinates.