Effect of 7S/11S ratio on the physicochemical properties of soy protein isolate-linoleic acid films

The effect of 7S/11S ratio on the physicochemical properties of soy protein isolate (SPI) and SPI-linoleic acid (LA) films was studied. The apparent viscosity in the film-forming solution and the oil droplet size in the film-forming emulsion increased with increasing 11S globulin ratio. The oil droplets in the SPI-LA films increased in number and floated to the surface when the 7S/11S ratio was 2:6. The tensile strength (TS) and elongation at break (EAB) of 7S globulin films were 9.45 MPa and 94.51%, respectively. The increase in the 11S globulin ratio increases the TS of SPI and SPI-LA films; however, their EAB did not change. As the 7S/11S ratio decreased, the water vapor transmittance of the SPI films and the SPI-LA films decreased, but their glass transition temperature and transparency values increased. The proportion of hydrogen bonds and non-disulfide covalent bonds in the SPI films and the SPI-oil films reduced with the increase in the 11S globulin ratio, whereas that of disulfide bonds and hydrophobic interactions increased. This study clarified the effect of 7S/11S ratio on the properties of SPI and SPI-LA films, providing the theoretical guidance for selecting suitable SPI for the preparation of edible films.