Abstract: In order to understand the mechanism for solubility improvement of soy protein isolate (SPI) by swirling cavitation treatment, changes in ionic bond, hydrogen bond, hydrophobic interaction, disulfide bond, and non-disulfide covalent bond contents of SPI after the treatment were evaluated and their relationship with the improvement in solubility of SPI was investigated. The results obtained were as follows: 1) the content of ionic bonds was increased with the increase in pressure and time; 2) the contents of hydrogen bonds and hydrophobic interaction were decreased with the increase in treatment time at 0.6 MPa, but they increased first and then decreased at 0.2 and 0.4 MPa; 3) the content of disulfide bonds was decreased with the increase in treatment pressure and time; 4) the content of non-disulfide covalent bonds did not change significantly at 0.2 MPa relative to the untreated group (P > 0.05), but was decreased at 0.4 and 0.6 MPa. Furthermore, the correlation analysis indicated that the solubility of SPI was correlated significantly positively with the content of ionic bonds (r = 0.754) (P < 0.01) and significantly negatively with the hydrophobic interaction and contents of disulfide bonds(r = ?0.714 and ?0.839, respectively) (P < 0.01). These results suggested that the improvement in solubility of SPI during swirling cavitation treatment was correlated with the formation of ionic bonds and the destruction of hydrophobic interaction and disulfide bonds.

Key words: swirling cavitation, soy protein isolate, intermolecular forces, solubility