PHYSICOCHEMICAL CHARACTERISTICS OF YAM STARCHES

Abstract

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 β-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.