Volume Effects of Starch-Water Interactions

Abstract

Volume changes arising from the sorption of water by three starches have been determined by dilatometry. By a recently described method, parameters of the G.A.B. equation have been used to resolve the volume changes into contributions from strongly sorbed water molecules in contact with the surface and from weakly sorbed water molecules in the remaining water layers. The latter produced only small volume effects. In contrast, the contact sorption caused very large volume decreases. Changes in these decreases with changing water content indicated two types of sorption sites, possibly crystalline and amorphous. In the case of waxy maize starch, for which literature data concerning its degree of crystallinity were available, the contact sorption could be quantitatively resolved into contributions from the presumably crystalline and amorphous portions, with the former exhibiting both higher affinity and larger volume changes for water molecules than the latter.