Freeze-thaw stability of oil-in-water emulsions stabilized by soy protein isolate-dextran conjugates

•Soy protein isolate-dextran conjugates were prepared by ultrasound and microwave.•The structures of SPI, SPI + D mixture, SPI-DU and SPI-DM were characterized.•SPI, SPI+D, SPI-DU and SPI-DM were used to stabilize oil-in-water emulsions.•The SPI-DU and SPI-DM emulsions exhibited a better freeze-thaw stability than SPI.•Glycosylation method improved the freeze-thaw stability of SPI emulsions.

The soy protein isolate-dextran (SPI-D) conjugates were prepared by ultrasound (power output 500 W for 40 min) and microwave (power output 800 W for 2 min) assisted glycosylation to improve the freeze-thaw stability of soy protein isolate stabilized oil-in-water (o/w) emulsions. Fourier transform infrared and fluorescence emission spectroscopy analyses confirmed that covalent bonds were formed between soy protein isolate (SPI) and dextran molecules through the Maillard reaction. The stability of SPI, SPI+D mixture, ultrasound SPI-D conjugates (SPI-DU) and microwave SPI-D conjugates (SPI-DM) emulsions subjected to from one to three freeze-thaw cycles was investigated. In comparison with SPI and SPI+D emulsions, SPI-DU and SPI-DM emulsions exhibited smaller creaming index, oiling off, droplet diameters, flocculation degree (FD) and coalescence degree (CD) after each freeze-thaw cycle. In addition, the zeta potential and specific surface area (SSA) were greater. Appearance and microstructure indicated that SPI-DU and SPI-DM emulsions exhibited a relative stable state after three freeze-thaw cycles.