PHYSICAL AND BARRIER PROPERTIES OF DEVELOPED BILAYER PROTEIN FILMS

Abstract

The effects of three bilayer–forming methods (liquid protein spread on dry film, heat pressing dry films, and solvent laminating dry films) on physical and barrier properties were investigated. These bilayer films were generated using soy protein isolate, wheat gluten protein, and corn zein protein. Bilayer films were evaluated for enhanced properties (tensile strength, percent elongation, water vapor, and oxygen permeability) over single layer films. Using X–ray crystallography, these films showed no changes in degree of crystallinity. Depending upon film type in this study, protein bilayer films exhibited reduced, similar, and enhanced properties. Hydration properties, solvent and protein interactions, film thickness, surface properties, or heat and pH differences influenced the formation of these films. Water vapor permeability for these films ranged from 1.3
10
9 g m –1 s –1 Pa –1 for soy sprayed on corn film to 3.5
10
9 g m –1 s –1 Pa –1 for solvent laminating wheat and soy films. Oxygen permeability ranged from 2.67
10 –17 moles m m –2 s –1 Pa –1 for spraying soy on corn films to 8.81
10 –19 moles m m –2 s –1 Pa –1 for pouring soy on wheat film. Tensile strength ranged from 1.57 MPa for spraying corn on wheat films to 9.10 MPa for heat pressing wheat and corn films. Elongation ranged from 5.36% for pouring soy on corn films to 204.12% for pouring soy on wheat films. Bilayer films appear to exhibit reduced tensile strength, similar oxygen permeability, enhanced percent elongation, and greatly increased water vapor permeability.