Microstructure and functional properties of sorbitol-plasticized pea protein isolate emulsion films: Effect of lipid type and concentration

• AMF and CNW increase surface hydrophobicity and reduce WVP of PPI films.
• Addition of lipids to the PPI films favors an increase in oxygen permeability.
• Addition of LEC produces porous films and increases film wettability and solubility.
• OLA does not form laminar structure and acts as a plasticizer.
• CNW gives the films with the most satisfactory functional properties.

The aim of this work was to compare the effect of increasing concentrations of anhydrous milk fat (AMF), candelilla wax (CNW), lecithin (LEC) and oleic acid (OLA) on the physicochemical and morphological properties of sorbitol-plasticized pea protein isolate (PPI) edible emulsion films. The lipids were incorporated into film-forming solutions at 0, 0.5, 1.0, 1.5, and 2.0%. It was found that among the tested lipids, only AMF and CNW reduced water vapour permeability (WVP) of the films, most likely due to their ability to increase film surface hydrophobicity. The greatest effect on the WVP reduction was achieved with CNW. The WVP of PPI films incorporated with 2.0% CNW was 2.5 times lower than that of the control. The incorporation of lipids into PPI films caused an increase in oxygen permeability. LEC destroyed the continuous structure of film matrix and caused an increase in film wettability and solubility. Increasing the amount of lipids in the films led to a decrease in mechanical strength. CNW-added films tended to have the best toughness properties. Unlike the solid lipids, OLA did not reduce the film transparency and showed a plasticizing effect, making the films more extensible. The addition of 2.0% OLA caused phase separation leading to the formation of discontinuity zones during film drying. Films with CNW had remarkably higher transparency compared to those of containing other solid lipids. All the resulting films were effective UV barriers. Surface microstructure of the emulsion films was influenced by the lipid type and lipid volume fraction.

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