Combining multi–spectroscopy analysis and interfacial properties to research the effect of ultrasonic treatment on soybean protein isolate–tannic acid complexes

Abstract

In this study, ultrasonic treatment of soybean protein isolate (SPI)–tannic acid (TA) non-covalent complexes were performed. In the multi-spectroscopic analysis, it was found that the content of the α-helix decreased, the exposure of amino acid residues increased, the content of the trans-gauche-trans mode of disulfide bonds increased, and the fluorescence intensity decreased. Static quenching occurred between TA and SPI, and ultrasonic treatment promoted their combination. The SPI–TA complexes had lower surface roughness at 450 W. At this moment, the volume mean diameter and zeta potential of the complexes were 70.76 nm and −22.4 eV, respectively. The surface hydrophobicity, solubility, contact angle, emulsification activity index, and emulsion stability index were 4,355, 73.2%, 49.71°, 117 m2/g, and 63 min, respectively. The diffusion rate of the sample under ultrasonic treatment at 450 W was 0.14777. Low-field nuclear magnetic resonance analysis revealed a higher percentage of immobilized water in the SPI–TA complex at 450 W. The above findings will help to promote the improvement in various aspects of the properties of SPI and enhance its application prospects.