Effects of Ultrasound-assisted Treatment on the Structural and Functional Properties of Rice Protein-Ferulic Acid Complex

This study investigated the preparation of rice protein (RP)-ferulic acid (FA) complex via ultrasound-assisted treatment, exploring both covalent and non-covalent interactions. The structure of these complexes was characterized using polyphenol grafting equivalents, sulfhydryl content analysis, UV spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. Furthermore, the solubility, surface hydrophobicity, and antioxidant activity of the complexes were evaluated. The results demonstrated that the ultrasound-assisted covalent complex exhibited the highest polyphenol grafting equivalent, reaching 25.49 μg FA/mg. Complexation with FA reduced the fluorescence intensity of RP, whereas the ultrasound-assisted treatment of the RP-FA complex led to an enhancement in RP fluorescence. Compared to non-ultrasonic treatment, ultrasound processing decreased the relative content of α-helix by 5.46% and 3.41% for covalent and non-covalent complexes, respectively. In addition, protein solubility was enhanced by 25.85% and 8.13% for covalent and non-covalent complexes prepared by ultrasound processing, respectively. Both DPPH and ABTS⁺ free radical scavenging abilities were significantly improved, with increases of 9.75% and 3.72% for DPPH and 10.45% and 2.06% for ABTS⁺, respectively, for covalent and non-covalent complexes after ultrasound treatment. Ultrasonic-assisted treatment significantly promoted the complexation of RP and FA, altered the structure of the complexes, and enhanced their functional properties, providing technical references and theoretical support for the application of rice protein-phenol complexes in fields such as food antioxidants and functional ingredients.