Enzymatic cross-linking of ewe's milk proteins by transglutaminase

Enzymatic cross-linking of ewe's milk proteins in the presence of transglutaminase was studied and the extent of cross-linking was analysed by capillary gel electrophoresis. Up to now, no publications are available that study the relative susceptibility of individual ewe's milk proteins. Transglutaminase has been demonstrated to induce cross-linking of the ewe's milk proteins. Moreover, a heat treatment of the milk before the reaction with transglutaminase enhanced the susceptibility of the individual ewe's milk proteins towards the cross-linking reaction. The specificity of transglutaminase has been shown to vary with the type of ewe's milk proteins (α_s2-casein, α_s1-casein, α_s0-casein, κ-casein, β-casein A¹, β-casein A², α-lactalbumin and β-lactoglubulin). From our findings, the reactivity for ovine α-caseins was reduced with respect to that of ovine κ-casein and ovine β-caseins. An optimisation strategy based on desirability functions together with experimental design has been used to optimise the preheating conditions (temperature and time) of ovine milk that maximised the cross-linking reactions catalysed by transglutaminase.