Structural heterogeneity in waxy-rice starch

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