Effect of ultrasonic pretreatment on the structure and emulsion stability of epigallocatechin-3-gallate and rice bran protein complex

To enhance the emulsion stability of RBP, the mixed solution of epigallocatechin-3-gallate (EGCG) and rice bran protein (RBP) was pretreated by increasing ultrasonic power (200-500 W). Ultrasonic pretreatment decreased the α-helix/β-sheet ratio (P < 0.05), and caused red-shift absorption peaks of intrinsic fluorescence and UV absorption spectroscopy of EGCG-RBP complex. With increasing ultrasonic power, combined phenol content, particle size, absolute value of ζ-potential, free -SH content, and surface hydrophobicity of EGCG-RBP complex initially rose, and subsequently dropped (P < 0.05). Compared with the EGCG-RBP complex without ultrasonic pretreatment, emulsifying activity index increased from 37.68 m2/g to 42.51 m2/g, and emulsion stability index increased from 123.00 min to 326.43 min as ultrasonic power was 425 W. The centrifugal stability constant, emulsion separation rate, and emulsion particle size initially dropped, and subsequently rose with increasing ultrasonic power. The emulsion stability of EGCG-RBP complex was correlated with particle size, absolute value of ζ-potential, α-helix/β-sheet ratio, free -SH content, and surface hydrophobicity (P < 0.05). Overall, ultrasonic pretreatment enhanced the EGCG-RBP interaction by regulating the absolute value of ζ-potential, flexibility and surface hydrophobicity of EGCG-RBP complex, thus improving emulsion stability, which provided a theoretical foundation for expanding the application of RBP in foodstuffs.