Aggregation and emulsifying properties of soybean protein isolate pretreated by combination of dual-frequency ultrasound and ionic liquids

The objectives of this study were to investigate the changes in the aggregation and emulsifying properties of soy protein isolate (SPI) pretreated with dual-frequency ultrasound and three different ionic liquids (ILs), tributyl methyl ammonium chloride ([TBMA]Cl), 1-butyl-3-methyl imidazolium chloride ([BMIM]Cl) and 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM]BF4). Results showed that dual-frequency ultrasound and ILs could not change the primary structure of SPI. The changes in UV-vis spectra indicated the unfolding of SPI as pretreated by [TBMA]Cl and [BMIM]Cl combined with dual-frequency ultrasound, followed by formation of soluble aggregates. The thermal stability analysis of the regenerated SPI suggested that [BMIM]BF4 presumably broke most of the hydrogen bonds within adjacent SPI molecules, leading to the decrease of thermal stability. Transmission electron microscopy showed major changes in protein morphology upon protein-protein interactions. SPI emulsion pretreated with dual-frequency ultrasound and [BMIM]BF4 had a higher emulsion stability index than the other samples (P < 0.05). Furthermore, as compared to untreated protein, all ultrasound and ILs pretreatments decreased the creaming index of SPI emulsion. These results indicated that combination of dual-frequency ultrasound and ionic liquids could be a potential method to change the aggregation and emulsifying properties of SPI. (C) 2020 Elsevier B.V. All rights reserved.