Melting behaviour of A- and B-type crystalline starch

The melting behaviour of highly crystalline spherulites, of a short chain amylose DP-15 corresponding to both the A and B polymorphs of starch has been studied as a function of water content. At water contents >40% w/w A-type spherulites melt at temperatures approximately 20°C higher than B spherulites, whilst both crystal forms melt at lower temperatures in the presence of increasing amounts of water. Using the Flory Huggins relationship for polymer crystal melting in the presence of a diluent, it is possible to predict a value for the ideal melting temperature of the dry crystals of 530 K.