A Study of the Internal Structure in Cassava and Rice Amylopectin

摘要

Cassava and rice amylopectins and their phi, beta-limit dextrins were debranched and the unit chain compositions were analyzed by gel permeation chromatography and high performance anion-exchange chromatography. The content of amylose and super-long amylopectin chains was 15.5-15.6% and 0.8-1.2% in cassava and 15.1-18.7% and 3.4-8.6% in rice starches, respectively. The internal unit chain profiles of the amylopectin samples were obtained from the phi, beta-limit dextrins. Short B-chains were subdivided into a major group (BS_(major)) with a degree of polymerization (DP) of 8-25 and a minor group of "fingerprint" B-chains (B_(fp)) with DP 3-7. Cassava and rice amylopectins possessed different amounts and patterns of B_(fp)-chains. The rice samples contained higher amounts of B_(fp)-chains, which suggested larger size of its clusters when compared with cassava. The content of the shortest "fingerprint" A-chains (A_(fp)) was also variable, especially between the rice cultivars. The position of the internal chains in the original amylopectin chain profile was traced. The reconstructed B-chain profiles fitted well with the original profiles. This implied that most of the B-chains carried external chain segments of similar lengths, which corresponded tothe experimentally measured average length.