Whey protein edible films modified with almond and walnut oils

Abstract

Whey protein isolate films with almond or walnut oils at low concentrations (0.5 and 1.0%) were prepared through emulsification in order to modify the functional properties of the films. Optical (colour and opacity), mechanical (tensile strength, Young's modulus, and elongation at break), barrier (water vapour, oxygen, and carbon dioxide permeability), surface (contact angle on both air and support film sides through time) properties and microstructure of whey protein emulsified films were determined. Bimodal distribution of oil droplets in film-forming solutions was observed by light scattering granulometry. The reduction of lipid droplet size upon increasing oil content caused weakened mechanical resistance of the films. Addition of oils leads to opaque films with heterogeneous microstructure, resulting in an increase in film opacity. The swelling, water vapour permeability, and surface hydrophilicity of the whey protein films were reduced due to the addition of the oils. An increase in oxygen and carbon dioxide permeability with increasing oil content was observed. Contact angle measurements through time showed the absorption of water droplets by the emulsified films, whereas the control film showed a swelling effect. Almond oil had a stronger plasticizing effect and was more effective in modifying the properties of whey protein films. The obtained results revealed that almond and walnut oils used at low concentrations enhanced the hydrophobic character of the whey protein films and have a good potential for incorporation into whey protein isolate to make edible films or coatings for some food applications.