Glycosylated cross-linked ovalbumin by transglutaminase in the presence of oligochitosan: Effect of enzyme action time and enhanced functional properties

This study investigated the effects of enzyme action time (1–5 h) on the physicochemical properties, structure, and functionality of transglutaminase-catalyzed ovalbumin (OVA) in the presence of oligochitosan (OCS). Physically combining OVA and OCS led to a substantial increase in particle size and polydispersity index, rendering the mixed system unstable. With the increase of enzyme action time, the particle size of glycosylated and cross-linked OVA (GC-OVA) decreased first and then increased, reaching a minimum value of 411 nm at 4 h. Moreover, the decrease of free amino groups content at 4 h reflected the occurrence degree of glycosylation and cross-linking reaction, which was close to saturation. Diverse methods were used to analyze variations in the molecular structure of OVA, confirming changes in the primary, secondary, and tertiary structures, and the microstructure. The glycosylation grafting and cross-linking with the appropriate extent of the enzymatic action time is the primary reason for improving the foaming, emulsification properties, and DPPH activity of OVA. Moreover, GC-OVA had greater apparent viscosity, G′ and G″ than the other control systems (the untreated OVA and the physical mixture of OVA and OCS) and significantly affected the hardness and cohesion properties in the gel's texture (5.6 and 2.4-fold that of the untreated OVA, respectively). This study provides information for further understanding the effect of glycosylation grafting caused by enzyme cross-linking time on OVA. The study also demonstrates the possibility of obtaining new protein compositions to expand the applications of food proteins.