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