Barrier properties of sodium caseinate films as affected by lipid composition and moisture content

Abstract

This work analyses the effect of lipid addition (oleic acid, beeswax and oleic acid–beeswax mixtures) as well as the influence of the relative humidity (RH), or the equilibrium water content of the films, on the permeability of sodium caseinate based films to water vapor and gas (oxygen and carbon dioxide). The effect that lipid addition had on the gas and water vapor permeability was dependent both on the composition of oleic acid–beeswax mixtures and the film’s moisture content. The addition of lipid mixtures reduced water vapor transfer as compared to the control films (without lipid), whereas pure oleic acid or beeswax were less effective. Both control films and films prepared with pure beeswax showed the lowest O2 and CO2 permeability, whereas the incorporation of oleic acid exponentially increased these values. A linear increase in water vapor and gas permeability was observed when the water content of the film rose, due to its plasticizing effect, which led to an increase in the molecular mobility. Predictive equations for water vapor permeability (WVP) and gas permeability were established as a function of water content and lipid composition.