Cereal Chem 47:437 - 446.  |  VIEW ARTICLE
Amylose Determination in Dimethyl Sulfoxide Extracts of Maize.

M. J. Wolf, E. H. Melvin, W. J. Garcia, R. J. Dimler, and W. F. Kwolek. Copyright 1970 by the American Association of Cereal Chemists, Inc. 

About 1 g. of corn is ground in 90% dimethyl sulfoxide (9:1 DMSO-water, v./v.) and then shaken for 24 hr. at room temperature to dissolve most of the starch. After undissolved solids are removed, the starch in 10 ml. of the clear extract is purified by precipitation with ethanol. The DMSO-starch precipitate is redissolved in 50 ml. of 90% DMSO. Starch in this solution is determined polarimetrically in an electronic polarimeter ([alpha]at 25 degrees, 549 nanometers =220 degrees). Amylose is determined spectrophotometrically on a separate portion of the same solution by measuring the absorbance of the amylose-iodine complex at 615 millimicrons. Purified linear starch fractions and waxy starch serve as reference standards for calibration. Amylomaize starches solubilize more readily in 90% DMSO than do either ordinary or waxy starches. However, the method is applicable to determination of amylose in the entire range of corn from ordinary corn to amylomaize. DMSO-extractable substances of germ and pericarp do not interfere with determination of amylose in endosperm starch. In fractional extraction of corn with DMSO, initial amylose content is high and decreases in successive extracts. Selective precipitation of starch with ethanol from crude DMSO extracts is equivalent to conventional solvent extraction as a means of minimizing fatty-acid interference with iodine sorption. Rate of amylose analysis is one and one-half to two determinations per man-hour.