Effect of Ultra‐high Temperature Treatment on the Enzymatic Cross‐linking of Micellar Casein and Sodium Caseinate by Transglutaminase

Abstract

ABSTRACT: It was found that ultra‐high temperature (UHT) treatment of sodium caseinate and native whey protein‐depleted micellar casein drastically increases the protein polymerization effect of an enzymatic treatment by microbial transglutaminase (TG). As a result the concentration of the isopeptide ε‐(γ‐glutamyl)lysine was increased significantly in UHT‐treated micellar casein solutions after TG incubation compared with the unheated casein solution. Sodium caseinate was more susceptible to the cross‐linking reaction as compared with the native casein micelles. The results demonstrate that the protein structure significantly affects the TG cross‐linking reaction. The effect of an UHT treatment was considered to be related to a better TG accessibility due to a more open casein micelle structure and to the inactivation of a TG inhibitor substance. The results demonstrate that an unidentified component in the natural milk serum inhibits the TG reaction. The thermal inactivation of a TG inhibitor is the dominant effect explaining the improved cross‐linking of UHT‐treated casein micelles as well as sodium caseinate.