Effect of microbial transglutaminase on the structural and rheological characteristics and in vitro digestion of rice glutelin-casein blends

The effect of microbial transglutaminase (MTGase) in cross-linking and modifying of rice glutelin-casein blends was investigated in this work. The maximum MTGase activity on rice glutelin-casein blends were found when its addition was 15 U/g of protein. Compared with the blends without MTGase, the appropriate addition of MTGase significantly affected the microstructure of the cross-linked proteins, resulting in the gradual 'burying' of Trp residue; while the space for hydrogen bonding was more abundant. Secondary structure changes, denoted by the disappearance of the alpha-helix and the decrement of the beta-sheet structure, was due to the formation of the large loop and random coil structures. The MTGase-catalyzed reaction improves the protease resistance of the blends but not promote the conversion of free sulfhydryl groups (-SH) to disulfide groups (S-S). All the samples evaluated exhibited Bingham flow behavior instead of shear-thinning behavior, and thermally stable fluid properties dominated by elasticity, regardless of MTGase concentration used. Both the storage modulus (G') and loss modulus (G") gradually decreased with the addition of MTGase. In short, this work demonstrated how the structure, rheology, digestibility of rice glutelin-casein blends are influenced by MTGase concentration.