Transglutaminase cross-linking kinetics of sodium caseinate is changed after emulsification

Enzymatic cross-linking is an important method of modifying the structure of food products to control their texture and stability. In this paper we look at the effect that adsorption to the oil–water interface of triglyceride oil-in-water emulsion has on rates of cross-linking of sodium caseinate by microbial transglutaminase. The kinetics of cross-linking has also been assessed for the individual casein proteins within the caseinate. In solution the rates were αs2-casein > β-casein > αs1-casein > κ-casein. This order is not as expected given the rheomorphic nature of the proteins and the number of glutamine and lysine residues in each protein. In particular, the αs1-casein was cross-linked much more slowly than expected. When sodium caseinate was adsorbed to an emulsion the rates for all constituent caseins were decreased but the cross-linking rate for αs1-casein was markedly reduced, indicating the most significant change in accessibility following adsorption. This knowledge will facilitate optimal production of cross-linked emulsions for use in future studies aimed at engineering emulsions with improved nutritional quality.