Molecular characterisation of waxy corn and barley starches in different solvent systems as revealed by MALLS

The effect of different dissolution procedures on molecular characteristics of waxy starches from corn and barley were evaluated using a MALLS (batch-mode) detector, principally to understand the role played by different solvents. Starches were dissolved in aqueous solutions of: (1) 90% DMSO, (2) 2 M KOH and (3) 90% DMSO/2 M KOH, and stored for 15 days at ∼22 °C with shaking. Weight-average molecular weight (Mw) and z-average radius of gyration (Rz) were determined at intervals ranging from 0 to 15 days. Regardless of starch source and dissolution procedures, Mw and Rz of amylopectin (AP) decreased with increasing storage time. Decrease in Mw followed the order: 90% DMSO > 2 M KOH > 90% DMSO/2 M KOH. However, decrease in Rz followed the order: 2 M KOH > 90% DMSO/2 M KOH > 90% DMSO. The study indicated that starch solubilisation in 90% DMSO/2 M KOH may be a reasonable method for molecular characterisation with less AP degradation.