Effect of drying temperature and beeswax content on moisture isotherms of whey protein emulsion film

AbstractThe objective of this investigation was to study the effect of drying temperature and beeswax (BW) content on moisture sorption behavior of whey proteins emulsion films. For this purpose, films were obtained by the casting method and dried at two selected temperatures (5 and 25°C) and constant relative humidity (RH) (58%). After drying, films were removed from the casting plates and were conditioned in the environmental chamber set at 25°C and 58% RH for 3 days. Subsequently, portions of 400mg of film were placed in glass bottles and pre-dried in desiccators containing drierite (aw=0) during 10 days. Then, the bottles were placed in hermetically sealed glass jars containing 10 different desiccants to achieve aw ranging from 0.11 to 0.90, and allowed to reach equilibrium. The analyses were made in quintuplicate at 25°C. The equilibrium moisture content (EMC) was determined by drying samples in an oven and the experimental data were fitted by the Brunauer-Emmett-Teller (BET) and the Guggenheim-Anderson-De Boer (GAB) models. The results showed that both models were effective to describe the moisture sorption behavior of the films. The GAB model gave better fit than the BET model. The increase of the drying temperature of 5 to 25°C and the incorporation of lipids reduced the EMC of whey protein emulsion films. Finally, data from experimental sorption isotherms are a useful tool to predict the effect of the environmental conditions that surround the film on its properties; particularly considering that the stability of an edible film is function of its mechanical and moisture barrier properties and both are strongly influenced by the presence of water, film formulation and drying and storage conditions