Amylose determination in genetically modified starches

The amylose contents of starches from various botanical origins (potato, smooth pea, wrinkled pea, wheat, maize) and from maize mutants [waxy (wx), amylose extender (ae), dull (du), sugary-2 (su2), aewx, aedu, dusu2 and wxdu] were determined by size exclusion chromatography (SEC), iodine-binding capacity (IBC) measurements, differential scanning calorimetry (DSC) and complexation with concanavalin A. SEC (with a 2.6×200 cm column) on HW75 S gel was used as the reference method for analyzing the macromolecular composition of starches. Variations in the fine structure of amylopectin affected its reactivity in classical methods such as IBC and were probably responsible for erroneous values in determinations when this polymer was the only starch component studied. When starches were composed of two macromolecules, all methods gave similar results, but with some discrepancies in DSC. The elution volume for a third class of alpha-glucans detected in some maize mutant starches was between that of amylopectin and amylose. Only SEC gave accurate results in this case since all other tested methods showed higher apparent amylose contents.