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 (M-w) and z-average radius of gyration (R-z) of amylopectin of selected starches. Ranges of M-w and R-z values of amylopectin were 7.0 x 10(7) -5.7 x 10(9) g/mol and 191-782 nm, respectively. Amylopectins of waxy starches had substantially larger M-w than did those of normal starch counterparts. Based on the dispersed-molecular density (M-w/R-z(3)), 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. M-w and R-z values of amylose isolated from amylomaize VII starch were also determined to be 2.8 x 10(5) and 43 run, respectively. (C) 2002 Elsevier Science Ltd. All rights reserved.