Water sorption properties of extruded zein films

Water interactions in extruded zein films were investigated through moisture sorption isotherms. Sorption isotherms of zein products were affected by composition and structure morphology. Zein powder showed moisture sorption hysteresis, which was not observed in extruded samples. Extruded samples held less moisture than zein powder, while films containing oleic acid showed further reduction in moisture uptake. Brunauer, Emmett, and Teller (BET) and Guggenheim, Anderson, and De Boer (GAB) models fitted well the moisture sorption isotherms of zein products. Monolayer values estimated by BET and GAB models were consistent with predictions based on zein structural models. Water vapor permeability (WVP) of zein films was affected by the relative humidity of testing environment. Higher relative humidity resulted in higher WVP.