In this study, soy protein isolate (SPI) was treated with hydrodynamic cavitation (HC) based on swirling. The texture properties, water-holding capacity, rheological properties, intermolecular force, microstructure, and secondary structure of transglutaminase-catalyzed SPI gel were determined to evaluate the effect of HC on the transglutaminase-catalyzed gelation behavior of SPI. The results showed that the gel strength (P < 0.05), water-holding capacity (P < 0.05), and storage modulus of the transglutaminase-catalyzed gel formed from SPI treated with HC for 30 minutes were increased significantly compared with the gel formed from untreated SPI. The intermolecular force for gel formation was changed. The contents of ionic bonds, hydrogen bonds and hydrophobic interactions were significantly decreased (P < 0.05), while the contents of disulfide bonds and non-disulfide covalent bonds were significantly increased (P < 0.05). Scanning electron microscopy showed that the transglutaminase-catalyzed gel formed from SPI treated by HC had smaller pores and more compact and uniform microstructure. The results of infrared spectroscopic analysis showed that the secondary structure of the gel was also changed by HC treatment. The contents of β-sheet and β-turn were increased significantly (P < 0.05), while the contents of α-helix and random coil were decreased significantly (P < 0.05). Therefore, HC treatment can improve the performance of transglutaminase-catalyzed SPI gel under certain conditions, and it may be used as an effective method in the food industry.

In this study, to understand the effect of hydrodynamic cavitation (HC) treatment on the interaction between catechin and soy protein isolate (SPI) and the structural and functional properties of the conjugates, we explored the changes in binding between catechin and SPI as well as the ultraviolet (UV) absorption and fluorescence spectra, free sulfhydryl and amino group contents, surface hydrophobicity, average particle size, zeta potential, secondary structure, and antioxidant properties of the formed conjugates before and after HC treatment. The results showed that HC treatment could promote the interaction between catechin and SPI. At 2.0 mg/mL catechin concentration, HC treatment could increase the amount of catechin bound to SPI from (21.82 ± 0.18) to (62.55 ± 0.36) mg/g. Compared with the untreated sample, HC treatment enhanced the UV absorption intensity, weakened the fluorescence intensity, increased the average particle size, decreased the absolute value of the zeta potential and surface hydrophobicity, and reduced the free sulfhydryl and amino group contents. Additionally, HC treatment caused an increase in α-helix, β-turn, and random coil relative contents and a decrease in β-sheet relative content. Furthermore, after HC treatment, the antioxidant activity of the catechin-SPI conjugates was significantly enhanced. For the conjugate formed at 2.0 mg/mL catechin concentration, the 1,1-diphenyl-2-picrylhydrayl (DPPH) free radical scavenging capacity increased from (48.64 ± 1.24)% to (84.72 ± 0.12)%, the 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging capacity from (35.60 ± 1.21)% to (75.51 ± 0.79)%, and the ferric reducing power from 0.81 ± 0.02 to 1.52 ± 0.05. It can be seen that HC treatment can promote the combination of catechin and SPI, change the structural properties of the resulting conjugates, and enhance its antioxidant activity.