Structural heterogeneity in waxy-rice starch

Alpha-amylase of B. amyloliquefaciens was used for the structural characteritation of the amylopectin from waxy-rice starch. Fractions of alpha-dextrins with a degree of polymerization (d.p.) < 5000 were isolated from amylopectin hydrolysates after 1 and 3 h. phi,beta-Limit dextrins were prepared by successive phosphorolysis and beta-amylolysis of the fractions and these were analysed by a second alpha-amylolysis. Based on the hydrolysis pattern, the limit dextrins were divided into two major groups, A and B, which possessed units of clusters of d.p. 100-200 and 90-130, respectively. An extensive alpha-amylolysis resulted in characteristic distributions of dextrins with d.p. < 80 which represented branched building blocks. Type A dextrins possessed more larger building blocks with d.p. similar to 40, but less intermediate and small blocks, than type B. The phi,beta-limit dextrin of the original amylopectin had a distinct distribution enriched in small building blocks. A model is proposed in which the two types of dextrins originate from regular and less regular structural domains of the amylopectin fraction within the starch granules. (C) 1999 Elsevier Science Ltd. All rights reserved.