Examination of the Structure of Amylose and Amylopectin by Fluorescent Labeling of the Reducing Terminal

Abstract

The fluorescent labeling/HPSEC method was developed and the molar-based distribution of amylopectin unit-chains, and molecules of amylose and amylopectin from various sources was examined. The molar-based distribution of A and B chains enabled the estimation of the number of chains per cluster. Cereal amylopectins had a larger number of chains in a cluster than root and tuber amylopectins. A-Crystalline type starches contained amylopectin with a larger number of chains per cluster than B-type crystalline. The molar distribution of C chain suggested the presence of long and short C-chains, which appeared to connect two clusters and were in single cluster, respectively. Amylopectin comprised three molecular species. The large species was major in amount by mole and weight, but the medium and small species were relatively large in amount by mole but very small by weight. The three species appeared to be built up with a similar cluster in structure and differed in the number of clusters. The number of clusters suggested that the large and medium species might be blocklets in granule while the small species immature and/or degraded products of the large species. Amylose comprised several molecular species with different size, and their proportions differed by plant sources. The small amylose species was predominant in cereal amyloses while the large amylose species in root and tuber amyloses. The number-average degree of polymerization of amyloses and the number average chain length of amylopectins determined by the labeling/HPSEC method were in good agreement with those determined by conventional colorimetric methods.