PARTITIONING OF WATER IN BINARY BIOPOLYMER MIXTURES AT LOW WATER-CONTENT

The dependence of the crystallinity of starch on water content has bee n used to monitor the amount of water associated with starch when it i s mixed with egg white or xanthan gum. Measurements of the water sorpt ion isotherms in the water activity range 0.2-0.9 predict that less wa ter is associated with the starch in the mixture than would be obtaine d for starch alone at the same water activity. This is confirmed by th e observed crystallinity. The effect can be quantified in terms of an interaction parameter xi which is the ratio of the water content of st arch in the mixture to that of starch alone at the same water activity . For starch/egg white mixture xi = 0.79, whereas for starch/xanthan g um mixtures xi = 0.9.