Micromorphological and Chemical Characterization of Starches in Dioscorea rotundata L. (White Yam)

Abstract

Starches isolated from twenty samples of Dioscorea rotundata L. (Dioscoreaceae) comprising ten local and hybrid cultivars each, were studied using micromorphological and chemical techniques. There is a marked polymorphism of granule shapes in all the samples, while the dimensions are more clear-cut, with granules exhibiting sizes >40 ?m accounting for 42.2% and 12% in local and hybrid cultivars, respectively. Solubility and swelling power are characteristic in the cultivars and follow similar increase patterns along the temperature gradient under investigation. However, the swelling power was relatively higher in the hybrid, than in the local cultivars, that suggest the chemical properties of D. rotundata starches are less affected by granule micromorphology, but more by the molecular and associative forces, which are intrinsic in the particular cultivar. The intergrading nature of granule morphology makes it an unsuitable attribute for discrimination among the cultivars. Therefore, solubility and swelling power, in combination with granule dimensions, may provide a secure technique for yam cultivar diagnosis, to be used in quality control and assurances, as well as in forensics. Okun, Sasanbula, Efuru and TDr97/00940 cultivars, which show lower solubility values could be important to diabetics and other health-conscious individuals while, Kokumo, Odo, Amula, Amuo, TDr98/01230, TDr95/18544, TDr95/9177, TDr8902565, TDr98/01217 cultivars which display higher solubility and swelling power may be important for dietary improvement and uses in pharmaceutical formulations.