Polarimetric determination of starch in corn with dimethyl sulfoxide as a solvent

Abstract

Polarimetric starch analyses in which starch is extracted from the corn kernel with 90% dimethyl sulfoxide (DMSO) at room temperature gave results in good agreement with those of the hot calcium chloride extraction customarily used. Recovery of different starches from corn varied in the following order of increasing difficulty: High-amylose, waxy, and ordinary. High-amylose starch was readily extractable; however, length of grinding and agitation time with DMSO governed the completeness of extraction of waxy and ordinary corn starches. More than 98% of the starch was recovered from amylomaize, waxy, and ordinary corn after 3, 6, and 9 min., respectively, of grinding in 90% DMSO. Heating (at 55°C.) without adequate shaking and grinding did not ensure quantitative starch recovery from ordinary and waxy corn. Such optically-active substances in corn as hemicelluloses, zein, and sugars did not interfere with starch determination by the new method. Rapid and accurate polarimetric readings were made by consecutively introducing sample solutions to a flow-through cell assembly.