The events leading to the formation of ghost remnants from the starch granule surface and the contribution of the granule surface to the gelatinization endotherm

During the process of gelatinization, the external layers of starch granules form granule envelopes which degrade into ghost remnants. These envelopes contribute to the gelatinization endotherm of starch through the controlled dispersion of internal starch polymer. Ghost remnants are shown to be derived from the external layers of the granules for a range of starches with different amylose/amylopectin ratios. The ghost remnants are composed primarily of amylopectin and exhibit elastic/plastic properties. The surface amylopectin is shown to be structurally distinct from internal amylopectin. During the early stages of granule gelatinization, high amylopectin starch granules swell by 200% in size, where the outer layer of the granule forms an envelope surrounding the disrupted internal starch polymers. High amylose starches do not swell, but do form envelopes at high temperatures ( greater than or equal to 90 degrees C). At a critical stress point the swollen envelope ruptures becoming a ghost, releasing the majority of the internal starch molecules, while a minority of the starch polymers remain trapped by the collapsed ghost. During the final stages of gelatinization the ruptured envelope degrades into ghost remnants. Manipulation of the starch granule surface, either genetically or chemically, would result in alteration of the gelatinization endotherm. (C) 1998 Elsevier Science Ltd. All rights reserved.