Improved emulsifying capabilities of hydrolysates of soy protein isolate pretreated with high pressure microfluidization

Abstract

Soy protein isolate (SPI) was treated by high-pressure microfluidization and pancreatin hydrolysis in this work. Results showed that microfluidization substantially enhanced pancreatin hydrolysis of SPI in terms of degree of hydrolysis (DH), with a preferable treatment condition at 120 MPa and 30 g/L SPI concentration. SDS-PAGE conducted under reducing conditions showed that microfluidization increased the accessibility of some subunits (α′-7S, A-11S and B-11S) in SPI to pancreatin hydrolysis, resulting in changes in protein solubility (PS), surface hydrophobicity (H0), and molecular weight distributions for hydrolysates. Emulsion systems (20 vol.% oil, 20 g/L protein samples, pH 7.0) formed by control SPI and SPIH (SPI hydrolysates) were unstable due to fast coalescence and bridging flocculation during homogenization, while that formed by MSPIH (microfluidization pretreated SPIH) with 5.8% DH was more stable and showed smaller mean droplet size (d43). Compared with SPIH, MSPIH showed a stronger increase in PS and a more moderate change in H0 during pancreatin hydrolysis, suggesting the production of more surface-active soluble peptides, which may explain their markedly improved emulsifying capabilities. This work showed that modified SPI could be an effective food emulsifier with microfluidization pre-treatment and limited proteolysis leading to desirable functional modifications of globular proteins.