Variability in starch physiochemical and functional properties of yam (Dioscorea sp) cultivated in Ivory Coast

Native starches were extracted from 21 cultivars of four yam species representative of the yam population of Ivory Coast. They were first characterized for their proximate composition, starch physico-chemical properties (amylose content, particle size distribution, crystallinity, thermal properties and intrinsic viscosity). Some functional properties (swelling, solubility and pasting behaviour and paste clarity) were then determined. Analysis of variance and principal component analysis showed that three homogenous groups could be distinguished, mainly based on starch physico-chemical properties. The first group contained all yam starches of the D alata and the D cayenensis-rotundata complex species. It was characterized by a large diameter grain (approximately 25 [mu]m), a high amylose content (around 25% db), a high intrinsic viscosity (mean of 190 cm3 g-1), and a high apparent viscosity and clarity of the paste. The second group contained the D esculenta varieties, characterized by a small granule size (diameter 6 [mu]m), a low intrinsic viscosity (121 cm3 g-1), a high gelatinization enthalpy change (19 J g-1) and a low paste viscosity. The D dumetorum sample differed from the D esculenta group by having a pure A-type crystalline form and an opaque paste. A multiple regression showed that the volume fraction of the dispersed phase and native granule size (or amylose content) could account for close to 80% of the variability of paste apparent viscosity. Gel clarity appeared mainly linked to granule size, small granules from D dumetorum and D esculenta giving the most opaque gels. (Résumé d'auteur