Fine structures of amylose and amylopectin from large, medium, and small waxy barley starch granules

Amylose and amylopectin were prepared from large, medium, and small granule starches of classified waxy barley flour, and their fine structures were investigated. The amylose content had a wide distribution range (approximate to1.4-9.4%). Number-average degrees of polymerization (DPn) of the amyloses were similar among the samples (approximate to1,200-1,300). But number of chains per molecule (NC) decreased from the surface to the center (approximate to6-10 chains). DPn of the amylopectins varied from 4,657 to 14,604; decreased in the order of large, medium, and small granules in same fractions of the grain; and increased from the surface layer to the center. Longest chains (LC) were not found in any of the amylopectin molecules. The large amylopectin molecule had more long chains and fewer A chains than the small molecule. The amylose content had definite effects on the transition temperature range and crystal formation of the starch granules. There were positive correlations between DP,of the amylopectin and relative crystallinity (gamma = +0.69) and enthalpy value (gamma = +0.80), respectively. These findings may help to elucidate biosynthesis mechanism of starch.