Hydrolysis of Native Starch of Some Wild Yam (Dioscorea) Species of Ivory Coast

The starch extracted from the tubers of some wild yam species Dioscorea praehensilis; Dioscorea hirtiflora; Dioscorea burkilliana; Dioscorea dumetorum; Dioscorea bulbifera and Dioscorea minutiflora are studied according to their sensibility to the hydrolysis acid (HCl 2.2 N at 35°C). Hydrolysis curves have two parts, a part with strong slope and another part with weak slope. The form of these curves agrees with the physical structure of the starch granule which has an amorphous zone and a crystalline zone. The acid hydrolysis of the amorphous zone corresponds to the part of the curve with the strong slope and that of the crystalline zone corresponds to the part with weak slope. The intersection of the weak slope portion tangent with vertical axis (Y-axis) is the starch easily hydrolyzed fraction. Fractions easily hydrolyzable (HF) are 5% (Dioscorea burkilliana); 10% (Dioscorea praehensilis); 12 % (Dioscorea minutiflora); 22 % (Dioscorea bulbifera (tuber); 22 % (Dioscorea bulbifera bulbil); 30 % (Dioscorea hirtiflora) and 36 % (Dioscorea dumetorum). The sensibility to the acid hydrolysis of the starch extracted from the various wild yam species studied varies in the following order: Dioscorea dumetorum > Dioscorea hirtiflora > Dioscorea praehensilis > Dioscorea bulbifera bulbil > Dioscorea bulbifera to tuber > Dioscorea minutiflora > Dioscorea burkilliana. It would be related to the size and the chemical composition of the grain of the starch. The studied starch of wild yam species altogether resists to the acid hydrolysis. © 2013 Agric. sci. dev. All rights reserved for TI Journals.