THERMOMECHANICAL BEHAVIOR OF WHEAT GLUTEN FILMS - EFFECT OF SUCROSE, GLYCERIN, AND SORBITOL

Glass transition temperature (T-g) and mechanical and water vapor barr ier properties of wheat gluten films containing glycerin, sucrose, gly cerin-sucrose, and glycerin-sorbitol were studied. Glycerin and sucros e were immiscible; the wheat gluten film containing both solutes showe d two separate thermal transitions (-58 degrees C and -5 degrees C, re spectively). The low temperature (low-T) transition (-58 degrees C) wa s due to a glycerin-rich region. The low-T tan delta peak height influ enced the tensile strength and elongation linearly and the water vapor permeability (WVP) curvilinearly. However, the T-g failed to change w ith solute composition and exhibited low correlation with barrier and mechanical properties. Initial addition of glycerin increased the WVP dramatically. Sucrose decreased the WVP (only slightly), but resulted in a rigid and fragile film. The gluten-glycerinsorbitol film at a rat io of 15:3:3 (w/w), 16.7% moisture (wb), showed a single effective T-g (-42 degrees C) and intermediate values for tensile strength, percent elongation, and WVP, which were between those of the 15:6:0 and 15:4:2 gluten-glycerin-sucrose films.