Formation of crystalline aggregates in slowly-cooled starch solutions prepared by steam jet cooking

Abstract

Spherocrystalline particles were formed in dilute, jet cooked solutions of normal cornstarch, high amylose cornstarch, rice starch and wheat starch, when hot solutions were allowed to slowly cool in insulated Dewar flasks. Yields ranged from approximately 7 to 12%, and particles were composed largely of amylose. Spherocrystals were not obtained from waxy cornstarch, defatted cornstarch or potato starch. Normal cornstarch, high amylose cornstarch and rice starch yielded mixtures of two different particulate species, each having its own unique size and morphology. Both species were strongly birefringent, and no significant loss of birefringence was observed when particles produced from normal cornstarch were heated in water to 97–99°C. Scanning electron microscopy (SEM) showed that smaller-sized particles were disc or torus-shaped and often exhibited spiral surface striations. The larger particles were approximately spherical in shape, and had rough surface textures. Wheat starch yielded only a single spherical small-particle species. X-ray powder diffraction patterns of small particle material matched patterns previously reported for the 6 1 amylose V-helical complex in the hydrated form. In contrast, diffraction patterns for large particle material suggested the 7 1 V-helical conformation for amylose. These results are consistent with the theory that spherocrystalline particles result from crystallization of helical inclusion complexes formed from amylose and the native lipid material present in cereal starch granules.