Enhanced hydrophobicity of soybean protein isolate by low-pH shifting treatment for the sub-micron gel particles preparation

Abstract In the present study, the soybean protein isolate (SPI) was treated by pH shifting process, as the protein was incubated in low pH solutions (pH 1.5–3.5) for 12 h, following neutralized to pH 7.0 and held for 4 h, which resulted in a conformation unfolding/refolding confirmed by the fluorescence spectra and a substantial increase in α-helix content revealed by circular dichroism (CD) spectra, along with the increased exposure of hydrophobic and sulfhydryl groups. In addition, the heat-induced gelation process and enhanced gel strength of pH 3.0 and 3.5 shifted SPIs were observed. Maillard reaction was then applied and the glycosylated SPI was further applied to the sub-micron gel particles formation. Results showed that low-pH shifting obviously improve the glycosylation ability of SPI as the conjugation degree and browning degree were enhanced. The sub-micron gel particles with core–shell structure and the average sizes of 100–250 nm were formed via heating self-assembly reaction and confirmed through Z-average of particle size, meanwhile, the increasing stability of gel particles in the solution was determined by Zeta potential analysis, suggesting that the improvement of hydrophobicity and glycosylated ability of SPI could promote gelling properties. Hence, the protein modification stage of pH shifting process would provide a great potential application in the formation of nano- or microscale gel particles.