Abstract
The effects of microbial transglutaminase (MTGase) cross-linking on the physicochemical characteristics of individual caseins were investigated. MTGase was used to modify three major individual caseins, namely, κ-casein (κ-CN), α(S)-casein (α(S)-CN) and β-casein (β-CN). The SDS-PAGE analysis revealed that MTGase-induced cross-linking occurred during the reaction and that some components with high molecular weights (>130 kDa) were formed from the individual proteins κ-CN, α(S)-CN and β-CN. Scanning electron microscopy (SEM) and particle size analysis respectively demonstrated that the κ-CN, α(S)-CN and β-CN particle diameters and protein microstructures were larger and polymerized after MTGase cross-linking. The polymerized κ-CN (~749.9 nm) was smaller than that of β-CN (~7909.3 nm) and α(S)-CN (~7909.3 nm). The enzyme kinetics results showed K(M) values of 3.04 × 10(-6), 2.37 × 10(-4) and 8.90 × 10(-3) M for κ-CN, α(S)-CN and β-CN, respectively, and, furthermore, k(cat) values of 5.17 × 10(-4), 1.92 × 10(-3) and 4.76 × 10(-2) 1/s, for κ-CN, α(S)-CN and β-CN, respectively. Our results revealed that the cross-linking of β-CN catalyzed by MTGase was faster than that of α(S)-CN or κ-CN. Overall, the polymers that formed in the individual caseins in the presence of MTGase presented a higher molecular weight and larger particles.