Molecular weights and gyration radii of amylopectins determined by high-performance size-exclusion chromatography equipped with multi-angle laser-light scattering and refractive index detectors

High-performance size-exclusion chromatography (HPSEC) equipped with multi-angle laser-light scattering (MALLS) and refractive index (RI) detectors was used to determine weight-average molecular weight (Mw) and z-average radius of gyration (Rz) of amylopectin of selected starches. Ranges of Mw and Rz values of amylopectin were 7.0×107–5.7×109 g/mol and 191–782 nm, respectively. Amylopectins of waxy starches had substantially larger Mw than did those of normal starch counterparts. Based on the dispersed-molecular density (Mw/Rz3), waxy amylopectins displayed, in general, larger dispersed-molecular density than did normal amylopectin counterparts, and amylopectins of the A-type starches had larger dispersed-molecular density than did those of the B-type starches. These results suggested that amylopectins of waxy starches had more branch-chains and no extra long chains, which resulted in more densely packed molecules than did those of normal starch counterparts. The amylopectin of B-type starch had longer but fewer branch-chains, which resulted in smaller dispersed density than did that of the A-type starch. Mw and Rz values of amylose isolated from amylomaize VII starch were also determined to be 2.8×105 and 43 nm, respectively.