Abstract: Ultrasonic treatment was used to promote the formation of complexes between red bean protein and lutein, and their structural and functional properties were measured and analyzed to explore the relationship between improvements in the functional properties and structural changes. The maximum binding rate between red bean protein and lutein was obtained by ultrasonic treatment at 240 W for 10 min. Thermal properties and Fourier transform infrared spectroscopy indicated the formation of red bean protein-lutein complexes, which reduced the surface hydrophobicity and free sulfhydryl content. Appropriate ultrasonic treatment reversed the decrease in both parameters and decreased the peak temperature and thermal enthalpy. The α-helix structure of the complexes was transformed into random coils under ultrasonic treatment, thus resulting in a looser and disordered structure, which might be related to the improved functional properties of the protein. Combination with lutein increased the solubility of red bean protein, but did not significantly change its emulsifying capacity, emulsion stability, foaming capacity and foam stability (P > 0.05). Ultrasonic treatment further increased the solubility of the complexes, and enhanced their emulsifying capacity, emulsion stability and foaming capacity. The most significant improvement was achieved by ultrasonic treatment at 240 W for 10 min. However, ultrasonic treatment had no significant effect on the foam stability of the complexes.

Key words: ultrasonic, red bean protein, lutein, structure, functional properties