Ultrasound-Assisted Transglutaminase Catalysis of the Cross-Linking and Microstructure of αs-Casein, β-Casein and κ-Casein

The effects of ultrasonic treatment (UT)-assisted transglutaminase (TGase) catalysis on the physicochemical properties of individual alpha(s)-casein (alpha(s)-CN), beta-casein (beta-CN), and kappa-casein (kappa-CN) were investigated. After 60 min of incubation at 30 degrees C, alpha(s)-CN, beta-CN, and kappa-CN were cross-linked with TGase (6.0 units/mL), and high molecular weight polymers (>200 kDa) were formed. The use of TGase in conjunction with UT (20 kHz, power of 400 W, and amplitude 20%) led to an increase in the rate of alpha(s)-CN, beta-CN, and kappa-CN polymerization compared to the individual casein that contained TGase but did not undergo UT. SDS-PAGE scrutiny showed that the intensities of alpha(s)-CN, beta-CN, and kappa-CN incubation with regard to TGase and UT at 30 degrees C for 60 min noticeably decreased to 5.66 +/- 0.39, 3.97 +/- 0.43, and 26.07 +/- 1.18%, respectively (p < 0.05). Particle size analysis results indicated that the molecule size appropriation for the cross-linking of alpha(s)-CN, beta-CN, and kappa-CN ranged from 6000 to 10,000 nm after 60 min incubation with TGase and UT. Transmission electron microscopy investigation showed network structures of cross-linking alpha(s)-CN, beta-CN, and kappa-CN were formed from alpha(s)-CN, beta-CN, and kappa-CN, respectively. As our results show, the comprehensive utilization of TGase and UT will be a superior method for the polymerization of alpha(s)-CN, beta-CN, and kappa-CN.