Origins of B-type crystallinity in glycerol-plasticised, compression-moulded potato starches

The amount of B-type crystallinity in compression-moulded, glycerol-plasticised potato starches was strongly dependent on both the properties of the potato starch used and the applied processing conditions. The presence of amylose and the morphology of the potato starch used, but also processing parameters such as moulding temperature and water content during moulding affected the amount of B-type crystallinity in the materials and thus the ultimate mechanical properties of the plasticised starches. This indicated that the direct relation between composition and physical properties of processed starches is not always valid; processing parameters are important tools for controlling the physical properties of processed starches as they influence the amount of B-type crystallinity in the material. It was shown that the total amount of B-type crystallinity in the glycerol-plasticised potato starches should be considered as a summation of residual amylopectin crystallinity and recrystallisation of both amylose and amylopectin, being strongly dependent on the applied processing conditions. In order to explain the observed amount of B-type crystallinity in these starches, partial (co-)crystallisation of both amylose and amylopectin should occur at high moulding temperatures. The measured mechanical properties of the plasticised potato starches correlated well with the amount of B-type crystallinity observed in the materials. (C) 1999 Elsevier Science Ltd. All rights reserved.