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Simultaneous quantification of allantoin and steroidal saponins in yam (Dioscorea spp.) powders

Lebot V., Faloye B., Okon E., Gueye B.. 2019. Journal of Applied Research on Medicinal and Aromatic Plants : 8 p..

Wild yams (Dioscorea spp.) are medicinal plants rich in secondary metabolites of pharmacological interest, mostly allantoin and steroidal saponins. Their natural populations are overexploited and endangered. Cultivated yams could represent an alternative source of metabolites if interesting varieties could be selected. The objectives of the present study were to develop an HPTLC protocol for the simultaneous quantification of allantoin and steroidal saponins in dried yam powders, to compare species and varieties originating from distant geographical origins and to assess their potential as a source of secondary metabolites. Overall, 1151 accessions belonging to six cultivated species were analysed (1000 acc. from Nigeria, and 146 acc. from Vanuatu) and were compared to five commercial powders of wild yam (D. villosa). Allantoin, dioscin, gracillin, protodioscin, protogracillin and five unknown saponins were quantified. Dioscorea villosa powders varied in content and composition, with allantoin ranging from 0.23 to 22.35?mg/g (DW) and total saponins from 37.36 to 129.97?mg/g. Allantoin was present in the six species, with highest values in D. bulbifera bulbils (20.38?mg/g) and D. cayenensis tubers (17.12?mg/g). Steroidal saponins were quantified in three species, D. cayenensis, D. esculenta and D. rotundata, but were absent in D. alata, D. bulbifera and D. dumetorum. Mean total saponins contents were 42.15?mg/g in D. cayenensis, 17.65?mg/g in D. esculenta and 17/44?mg/g in D. rotundata, with accessions presenting very high values in D. cayenensis (78.31?mg/g) and D. rotundata (69.65?mg/g). For both allantoin and saponins, variation was observed within tubers and the tuber peel was richer than the flesh. Cultivated yam species represent a sustainable source of allantoin and steroidal saponins which could be further increased through conventional breeding.

Mots-clés : métabolite secondaire; allantoïne; saponine; pharmacologie; composition chimique; poudre; igname; dioscorea; vanuatu; nigéria

Thématique : Composition des produits alimentaires; Autres thèmes; Génétique et amélioration des plantes

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