超声对豌豆分离蛋白结构及乳化性能的调控效应

Objective: This study was designed to investigate the effects of ultrasonic treatment on the structure and physicochemical properties of pea protein isolate (PPI), and to explore the regulation mechanism of ultrasonic treatment on the emulsifying characteristics of PPI, so as to provide the theoretical basis for the application of PPI as natural emulsions or related products in the food field. Method: The ultrasonic-pea protein isolate (U-PPI) was prepared by ultrasonic wave with frequency of 20 kHz and power of 600 W under different times (0, 20, 30, 40 and 60 min), and then U-PPI emulsions were prepared by high pressure homogenization. The effects of ultrasonic treatment on the physicochemical properties of PPI were investigated by the tests of free amino group, total sulfhydryl group, particle size, solubility and SDS-PAGE. The changes in secondary and tertiary structure of U-PPI were analyzed by circular dichroism and intrinsic tryptophan fluorescence, respectively. The emulsifying ability and emulsion stability of U-PPI were characterized by emulsion activity index, particle size, protein distribution at the interface of emulsion, Zeta potential and apparent viscosity. The microstructure of the emulsions was observed by using laser confocal fluorescence microscopy. Result: Ultrasonic treatment significantly modified the structure of PPI, i.e., a short time (30 to 40 min) ultrasonic treatment significantly reduced the α-helix content and improved the β-sheet content of PPI, which made the structure of the PPI more flexible and more hydrophobic groups exposed to the interface. Simultaneously, the depolymerization effect of ultrasonic also caused the decrease of the average particle size and the significant increase of the solubility of PPI. Therefore, the modification of PPI by a short time ultrasonic treatment was conducive to the formation of a dense and stable protein film at the oil/water interface, which effectively improved the emulsifying activity of PPI and the stability of the emulsions, and the microstructure of the emulsions also showed that the particle sizes of emulsions stabilized with U-PPI were smaller, and the droplet distribution was more uniform. However, a long time (60 min) ultrasonic treatment caused the hydrophobic repolymerization and insolubility of PPI, which was not conducive to the adsorption and rearrangement of PPI in the oil/water interface and thus reduced the emulsifying activity and emulsion stability. Conclusion: The cavitation effect and mechanical effect produced by a short time (30, 40 min) ultrasonic treatment had significant depolymerization effect on PPI, which promoted the protein structure more flexible and was beneficial to the adsorption and rearrangement of PPI at the oil/water interface, and thus significantly improved the emulsifying properties of PPI.