Starch from tubers of Dioscorea alata, Dioscorea cayenensis, Dioscorea dumetorum, and Dioscorea rotundata was isolated and some of the important characteristics determined. Amylose and amylopectin fractions were obtained by aqueous leaching technique. All the starches appeared to have definite but minor differences in iodine binding capacity, swelling power, solubility, intrinsic viscosity, and amylose/amylopectin ratio. Brabender amylogram of each starch showed no distinct peak viscosity, and the general amylograph pattern was distinctly different from typical amylographs of cereal starches. Amylose fractions from each starch variety exhibited variable degree of fl-amylolysis limits ranging from 92-97.5%, and an average molecular weight for amylose triacetate of 210,000 to 265,000. Amylopectin fractions subjected to debranching by pullulanase gave essentially two chain populations of polysaccharides with degree of polymerization of approximately 13-27 and 47-65, respectively. Average unit chain length of the amylopectins ranged from 19 in Dioscorea rotundata to 24 in Dioscorea dumetorum.

Water-soluble nonstarchy polysaccharides (WSNP) and waterinsoluble nonstarchy polysaccharides (WINP) of pearl millet (Pennisetum typhoides) were isolated, purified and characterized for carbohydrate composition. Gas-liquid chromatographic analysis of the derived alditol acetates obtained from hydrolyzed WSNP, WINP and their respective DEAE-cellulose fractions revealed similarities in carbohydrate content, but marked differences in distribution pattern. Rhamnose, ribose, L-arabinose, xylose, mannose, galactose, and glucose were detected. Sepharose 4B chromatography confirmed arabinoxylan as the predominant polysaccharide, with significant amounts of arabinogalactan, and glucan noticeable in some fractions. UV spectral analysis and thin-layer chromatography showed ferulic acid as the major phenolic compound, in addition to caffeic acid and two other unidentified phenolic acids.

alpha-Amylase from germinating tubers of a yam Dioscorea dumetorum was extracted and purified by four steps of purification. A total yield of 23.1% was obtained with over 1,600-fold increase in specific activity. Three distinct amylolytically active protein forms were resolved upon treatment of the preparation on DEAE-cellulose ion exchange chromatography at pH 8.3. All the partially purified alpha-amylase fractions have similar physical properties with respect to pH optimum, Km values, molecular weights, and energies of activation. Qualitative paper chromatographic analysis of the alpha-amylase-amylose digest revealed variable product specificity for the three alpha-amylase fractions. One form exhibited a dual product specificity for the formation of maltose and maltohexaose, while another form produced exclusively maltopentaose from polysaccharide substrates. The third amylase fraction showed usual action pattern characteristic of most alpha-amylases.