Surface Evaluation of Resin Zein Films Containing Sugar Plasticizers by Permeability and Atomic Force Microscopy Analysis

Zein is one of the best biopolymer for edible film making and sugars are natural plasticizers for biopolymers. In this research, sugars (fructose, galactose and glucose) at three levels (0.5, 0.7, 1 g/g of zein) were used as plasticizers for zein protein films and their water vapor permeability (WVP), oxygen permeability (OP) and atomic force microscopy (AFM) topography were studied. The pure zein films had the highest WVP and adding sugars to 0.7 g/g of zein decreased WVP of the films. In comparison among different zein films, those plasticized by galactose and fructose had the highest and lowest barrier properties, respectively. The zein films without plasticizer had low OP and increasing plasticizers to 0.5 g/g of zein decreased OP values in all samples. The films containing galactose and fructose had the lowest and highest OP, respectively. AFM images were used to evaluate surface topography (a qualitative parameter) and roughness (a quantitative parameter) of the zein films. The films plasticized by fructose had smoother surface and lower roughness than the other films. Interrelation between WVP, OP and the roughness of zein films were not observed.