Transglutaminase-induced cross-linking of vicilin-rich kidney protein isolate: Influence on the functional properties and in vitro digestibility

The covalent cross-linking of vicilin-rich protein isolate from kidney bean (KPI) by microbial transglutraminase (MTGase; at an enzyme-substrate ratio of 5.0 units per gram protein) was characterized by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) and size exclusion chromatography combined with multi-angle laser light scattering (SEC–MALLS). Effects of MTGase treatment on some functional properties and in vitro trypsin digestibility of KPI were evaluated. SDS–PAGE and SEC–MALLS analyses indicated that MTGase polymerized the vicilin component in KPI to form high molecular weight oligomers or biopolymers, and the cross-linking occurred among intermolecular and intramolecular subunits. MTGase treatment led to a significant decrease in total free SH content and an increase in surface hydrophobicity, suggesting unfolding of the vicilin molecules. Protein solubility, emulsifying activity index, and emulsion stability index of KPI were progressively decreased with increasing MTGase incubation time. Thermal stability and in vitro trypsin digestibility of the vicilin component were gradually and significantly increased. These results suggest that functional properties of vicilin-rich KPI could be negatively affected by the enzymatic cross-linking, while nutritional property might be markedly enhanced.