Effect of water partitioning on the glass-transition behaviour of phase separated amylopectin-gelatin mixtures

The glass transition behaviour of concentrated 1:1 and 3:1 amylopectin-gelatin mixtures (water contents between 18 and 36% dry basis) was studied for different compositions using FTIR microspectroscopy and DMTA. The thermograms of these mixtures exhibited 2 transitions indicating the existence of 2 phases. This was in agreement with the FTIR microspectroscopy results where 50-80 mu m amylopectin-rich regions could be clearly identified in the continuous gelatin matrix. The assignment of the DMTA transitions was ascertained by varying the gelatin/amylopectin ratio. The prediction of the T-g for each of the 2 phases based on the existing values for the binary systems was best accomplished when the water partitioning between the polysaccharide and the protein was accounted for using the water vapour sorption/ desorption isotherms of the individual biopolymer components of the blend. Finally, typical glass transition - "water partitioning" phase diagrams of phase separated amylopectin-gelatin mixtures were constructed. (C) 1999 Elsevier Science Ltd. All rights reserved.