INFLUENCE OF MICROBIAL TRANSGLUTAMINASE ON SOME PHYSICAL AND MICROSTRUCTURAL PROPERTIES OF COW MILK COAGULUM SUPPLEMENTED WITH WHEY PROTEINS

Recently, a focus on the utilization of whey proteins (WP) has been extensively investigated due to their nutritional value and their potential to enhance functional characteristics of the dairy product. The effect of microbial transglutaminase (TG) on the characteristics of skim-milk prepared with the addition of WP products (α-lactalbumin, β-lactoglobulin and whey protein isolate (WPI)) was studied. For comparison, full-fat and skim-milk gels without addition of TG were also examined. The results show that TG significantly (P<0.05) increased the yield values and decreased curd firmness obtained by formagraph, compared to skim-milk gel without TG. Furthermore, addition of WP enhanced the reactivity of TG as indicated by the extended rennet coagulation time and the further less firmness of the curd. This result was confirmed by the appearance of new high molecular weight protein polymers bands in SDS-PAGE, particularly, within WPI and β-lactoglobulin treatments. The highest curd yield was obtained when WPI was added (an increase of ~50 %, compared with the TG-treated skim-milk), while the α-lactalbumin addition exhibited the least reactivity with TG on coagulation properties. Also, scanning electron microscope (SEM) analysis approved the same trend of the results represented in the more dense structure accompanied by finely dispersed clusters of WP strands attached to protein matrices with particular intense in WPI and β-lactoglobulin treatments. In conclusion, the cross-linking by TG with the addition of whey proteins intensely altered the functional properties of the resulting milk coagulum. This novel functionality of the milk coagulation network offers interesting possibilities for enhancing dairy products by adding whey proteins before treating milk with TG.