Relationship between structure and function of soybean isolated protein complexes in ultrasound-assisted L-histidine modified during genipine cross-linking

This study delved into the impacts of ultrasound-assisted L-histidine (L-His) on the physicochemical attributes and structure of soy protein isolate (SPI) during genipin cross-linking. Particle size, ζ-potential and scanning electron microscopy were employed to assess the protein aggregation induced by cross-linking. Meanwhile, spectral analysis, surface hydrophobicity, thermal stability, solubility and antioxidant properties were utilized to characterize the correlation between protein structure and functional alterations. After genipin cross-linking, owing to the elevation in the contents of α-helix, β-sheet, and β-turn, along with the shrinkage effect, SPI presented a smaller particle size. Consequently, the complex system became more stable, and the rigidity of the protein structure was enhanced. Additionally, spectral analysis revealed that an optimal concentration of L-His could facilitate better cross-linking between genipin and the complex and modify the micro-environment of amino acid residues in SPI. As a result, its solubility and antioxidant properties were improved. Notably, when the L-His concentration reached 0.2 wt%, the complex manifested the most stable structure and exhibited superior functional properties. • SPI structure was modified using genipin and ultrasonic L-His. • The G-USL complex features an ordered structure and enhanced rigidity. • L-His amounts affected USPI-L-His complexs' cross-linking degree with genipin. • Genipin enhanced the thermal stability of the USPI-L-His complex.