Amylose determination in genetically modified starches

The amylose contents of starches from various botanical origins (potato, sm ooth pea, wrinkled pea, wheat, maize) and from maize mutants [waxy (wx), am ylose extender (ae), dull (du), sugary-2 (su2), aewx, aedu, dusu2 and wxdu] were determined by size exclusion chromatography (SEC), iodine-binding cap acity (IBC) measurements, differential scanning calorimetry (DSC) and compl exation with concanavalin A. SEC (with a 2.6 x 200 cm column) on HW75 S gel was used as the reference method for analyzing the macromolecular composit ion of starches. Variations in the fine structure of amylopectin affected i ts reactivity in classical methods such as IBC and were probably responsibl e for erroneous values in determinations when this polymer was the only sta rch component studied. When starches were composed of two macromolecules, a ll methods gave similar results, but with some discrepancies in DSC. The el ution volume for a third class of alpha -glucans detected in some maize mut ant starches was between that of amylopectin and amylose. Only SEC gave acc urate results in this case since all other tested methods showed higher app arent amylose contents. (C) 2000 Elsevier Science Ltd. All rights reserved.