Characterization of emulsion films prepared from soy protein isolate at different preheating temperatures

The effect of soy protein isolate (SPI) preheating temperature on the physicochemical properties of SPI-oil emulsion (SPI-OE) films was investigated. Tensile strength (TS) and elongation at break (EAB) of the SPI-OE films prepared from SPI preheated at 45 degrees C were 7.90 MPa and 59.30%, respectively. The TS of the SPI-OE films increased with the preheating temperature of SPI, whereas the EAB first increased and then decreased. Discrepancy between the contact angles in the upper and lower surfaces of the films gradually increased with preheating temperature. When the preheating temperature of SPI was higher than 75 degrees C, oil droplets accumulated on the upper surfaces of the SPI-OE films, as shown in the scanning electron micrographs, and the intensity of absorption peak (1744 cm(-1)) obtained through infrared spectroscopy decreased. No obvious change in protein molecular weight was found in the SPI-OE films with increasing preheating temperature, but the glass transition temperature increased.