Investigation of Water Vapour Permeability, Hydrophobicity and Morphology of Zein Films Plasticized by Polyols

Zein (prolamin of corn) has good film forming properties. The pure zein film is very brittle and plasticizers can improve its mechanical and film making properties and represses its permeability to gases. Polyols are natural plasticizers for food biopolymers. In this research, three types of polyols (sorbitol, manitol, and glycerol) were used as plasticizers and the water vapour permeability (WVP), contact angle and microstructure of different zein films were studied. The pure zein film had high WVP and adding glycerol and sorbitol by 0.7 g/g zein lowered WVP but this effect was not observed in films containing manitol. The films containing glycerol had the lowest WVP. The zein films containing glycerol had the highest water contact angle compared with the plasticized films. The pure zein films and the films containing manitol had the higher critical surface tension of wetting (γc) than the films containing glycerol and sorbitol. Adding polyols to zein films increased the surface tension of the zein films. In the unplasticized zein films and those plasticized by manitol, loose structural integrity and a lot of cavities and voids have been detected. The films plasticized by glycerol had smooth glassy surface.