Preparation and characterization of composite sodium caseinate edible films incorporating naturally emulsified oil bodies

Oil bodies in the form of a naturally emulsified emulsion were recovered from maize germ by applying aqueous extraction and were then exploited in the preparation of composite sodium caseinate-based films. Following equilibration of the initial film-forming dispersion, the caseinate molecules appeared to adsorb to the oil droplet surface facilitating thus the dispersion of the latter in the protein solution. During the course of film formation partial destabilization of oil body dispersion took place as a result of depletion by non-adsorbed caseinate. The finally formed composite films differed from the control, both in their surface characteristics as well in physicochemical and tensile properties. The oil-incorporating films were less transparent, less hydrophilic and, as a result, more resistant to water sorption and vapor permeation than the oil-free caseinate films. In addition, the composite films exhibited higher flexibility and lower stiffness. These findings are discussed in terms of the formation during the drying step of a composite caseinate-based phase separated structure embedded with oil bodies having their surface in intimate association with the protein molecules of the continuous protein matrix.