Physicochemical Properties of Soybean 11S Globulin-Based Films Affected by Linoleic Acid Concentration

In order to explore the interaction between lipid and protein in film-forming solutions and films, the effects of linoleic acid concentration (0%, 10%, 20%, 30% and 40% relative to protein mass) on the viscosity of 11S globulin film-forming solutions, and the microstructure and physicochemical properties of the resulting films were studied. Confocal laser scanning microscopic (CLSM) images showed that the size of oil droplets in the film-forming solution increased with increasing linoleic acid concentration, and it further increased after drying. According to the results of scanning electron microscopy (SEM), oil droplets accumulated on the upper surface of the smooth and dense protein films after adding linoleic acid, while the lower surface became rough without accumulation of oil droplets on it. After adding 40% linoleic acid, the glass transition temperature, tensile strength and water vapor permeability of the film decreased from 53.50 ℃, 12.67 MPa and 2.52 × 10^-10 g/(m·Pa·s) to 50.38 ℃, 7.30 MPa and 1.83 × 10^-10 g/(m·Pa·s), respectively, while the elongation at break increased from 95.58% to 198.15%. Molecular dynamics simulation showed that 11S globulin did not interact with linoleic acid below 200 ns. The proportion of ionic bonds and disulfide bonds in the 11S globulin film decreased with the addition of linoleic acid, while the proportion of hydrophobic interactions and non-disulfide covalent bonds increased. These results suggest that the addition of linoleic acid can change the chemical interactions among proteins, thus affecting the physicochemical properties of the film. This finding provides a theoretical reference for studying the mechanism of film formation of soybean protein emulsion films.