Emulsions-filled films made of glycerol, corn oil, and whey protein isolate

Abstract

This study investigates the effect of different corn oil concentrations (0%, 6%, 8%, and 10% w/w) and environmental moisture on moisture uptake, water vapor permeability, tensile properties (stress and elongation at break), and optical characteristics of edible films based on glycerol-plasticized whey protein isolate (WPI) films. The purpose was to assess the potential of these biopolymer films as sustainable food packaging materials. According to mechanical tests, moisture content and oil both function as plasticizers, increasing elongation at break and decreasing tensile strength, confirming the plasticizing effect of both water and oil. In films with high oil concentrations, non-uniform oil distribution was observed, which could compromise mechanical integrity. Barrier properties, including water vapour permeability (WVP) and moisture uptake, were significantly influenced by oil concentration. The high oil content in the membranes in combination with relative humidity led to a reduction in moisture sorption and water vapor permeability, due to the microstructural changes, caused by the addition of oil, and affecting water diffusion. Slightly changes occurred during colour analysis including whiteness and luminosity, and slight increases in opacity were observed by increasing oil concentration. This was attributed to light scattering by oil droplets. Also, chroma slightly increased with oil concentration, particularly at 10%.