Effect of plasticizing sugars on water vapor permeability, surface energy and microstructure properties of zein films

Sugars are natural plasticizers for food biopolymers and zein is the most important protein of corn. In this research, sugars (fructose, galactose and glucose) were used as plasticizers and the water vapor permeability (WVP), contact angle and microstructure of the zein films were studied. The pure zein film had high WVP and adding of sugars to 0.7 g/g zein caused to decrease of WVP. Films containing galactose had the lowest WVP. All samples had the lowest contact angle with ethanol and the highest contact angle with water. The zein films containing galactose had the highest water contact angle within the plasticized films. The pure zein films and the films containing fructose had higher critical surface tension of wetting (y(c)) than the films containing glucose and galactose. Adding sugar plasticizer to zein films increased the surface tension of zein films. In the unplasticized zein films, loose structures with a lot of cavities and voids were observed. The films plasticized by fructose had smooth surface and plasticizer particles distributed throughout of the films. (C) 2006 Published by Elsevier Ltd. on behalf of Swiss Society of Food Science and Technology.