Physicochemical properties, structural characteristics and in vitro digestion of brown rice–pea protein isolate blend treated by microbial transglutaminase

The present study sought to use microbial transglutaminase (MTG) to modulate the physicochemical properties of brown rice protein isolate (BRPI), pea protein isolate (PPI) and their blend, and determine MTG's effect on protein structural and digestive profile changes. MTG at concentration of 1 U/g significantly increased water holding capacity (91.6% enhancement) and decreased oil holding capacity (39.3% reduction) of BRPI + PPI (4:6) blend, respectively, accompanied by decreasing their solubility and zeta potential values in aqueous system. From rheological analysis, MTG-induced crosslinks could result in stronger and more elastic gels in BRPI + PPI blend with lower gel point temperature. SDS-PAGE demonstrated that the number and intensities of the protein bands for all MTG-treated BRPI were similar under both non-reducing and reducing conditions, whereas in the samples containing PPI, fewer and fainter bands were shown in the groups treated by MTG at concentration of 4 U/g and above. From FTIR spectra, lower level of random coils paralleled by an increase in both β-sheet structures and α-helix band were observed in the 1.0 U/g MTG-treated BRPI + PPI blend, indicating the protein-protein interactions within the mixed systems might boost the role of MTG in the structural modification, facilitating the network formation of more ordered structure with better thermal stability. Results of in vitro digestion showed less hydrophobic amino acids and essential amino acids including Lys released in MTG-treated BRPI + PPI blend's digests. Overall, the application of MTG in plant-based proteins can potentially contribute to the development of innovative food products with modified functionalities and unique digestive characteristics.