Effect of ultrasound treatment on kidney bean protein isolate-oat β-glucan glycation conjugates: The structure, digestibility and emulsifying properties

Conjugates of kidney bean protein isolate (KBPI) and oat β-glucan (OG) were successfully prepared via ultrasonic-assisted Maillard reaction (wet heating). The effects of ultrasonic power density (9.62-29.37 W/cm²) on its structural characteristics, in vitro digestive behavior, and emulsifying properties were investigated. The results demonstrated that ultrasonic treatment significantly enhanced the covalent conjugation between KBPI and OG. Specifically, the ultrasonically modified conjugate (UHKBPI-OG3) prepared at 22.42 W/cm² exhibited higher grafting degree of 23.53 %. Appropriate ultrasonic treatment reduced the average particle size and polydispersity index (PDI) of conjugates, as well as increasing the absolute value of their ζ-potential. Circular dichroism (CD) analysis revealed that ultrasound-assisted wet heating induced conformational changes in KBPI, showing a significant reduction in α-helix content accompanied by an increase in random coil structure. This structural transition suggests enhanced molecular flexibility, which is favorable for achieving higher glycosylation efficiency. Ultrasonic treatment enhanced the emulsifying properties of UHKBPI-OG3, increasing emulsifying activity index (EAI) and emulsion stability index (ESI) by 20.75 % and 15.65 %, respectively, compared to wet heating. Concurrent reductions in interfacial tension, apparent viscosity, and droplet size further contributed to improved emulsion stability. Furthermore, UHKBPI-OG3 conjugate (24.22 W/cm²) exhibited the lowest protein digestibility. These findings demonstrate that optimized ultrasonic power density enhances KBPI-OG covalent conjugation. The improved functional properties of conjugates, achieved through modulated protein-polysaccharide interactions, provide theoretical support for developing novel emulsion stabilizers.