Functional properties of soy protein isolate edible films as affected by rapeseed oil concentration

The effect of the rapeseed oil concentration at 0, 1, 2, and 3% (w/w) on the optical, mechanical, barrier, sorption, and surface properties of soy protein isolate films was evaluated. Bimodal distribution of the oil droplets in film-forming emulsions and decreased volume-surface diameter (D-3(,2)) as a result of oil concentration were observed. The opacity and total colour differences were significantly increased by incorporating oil. A noticeable decrease of water vapour permeability of films with increasing oil content was observed for all relative humidity (0-50%, 50-75%, and 50-100%). Tensile properties and contact angle analysis showed that oil-containing films exhibited weakened properties. The significant improvement of film hydrophobicity due to the addition of oil was observed during the first 24 h in the water vapour sorption analysis. The microstructure of the films changed after the addition of oil from homogeneous and smooth to heterogeneous and rough.