THE GRANULAR STRUCTURE OF C-TYPE PEA STARCH AND ITS ROLE IN GELATINIZATION

We have used a combination of techniques to study the structure and pr operties of C-type starch from pea seeds. It was found that all C-type starch granules contain both types of polymorph; the B polymorphs are in the center of the granule and are surrounded by the A polymorphs. During heating in excess salt solution the A and B polymorphs within C -type granules melt independently, giving a double transition in heat capacity and a two-step swelling, compared with single transitions for A-and B-type starches. It was shown that B polymorphs gave a transiti on with a lower peak temperature than A. The disruption of crystallini ty during gelatinization began from the hilum area and was propagated along the granule, accompanied by swelling of disrupted areas. It is p roposed that the swelling of disrupted parts of the granule decreases the melting temperature of the neighboring crystallites resulting in t he progressive disruption of crystalline areas. The gelatinization pro cess is dependent on the arrangement of A and B polymorphs within the granule. (C) 1998 John Wiley & Sons, Inc.