Title : Saponins profiling of yam (Dioscorea spp.) using UHPLC-DAD-MS as related to their nutritional quality
Abstract:
Yam, a member of the Dioscoreaceae family and the Dioscorea (D.) genus, is an edible tuber well known to be one of the main sources of steroidal saponins in the plant kingdom. In rodents, consumption of yam or dioscin extracts has been shown to reduce food intake and obesity and to improve the control of diabetes. To cope with the global obesity epidemic, which heavily affects some tropical countries, yam could play an important role in limiting metabolic diseases. The saponin profile was established using freeze-dried yam powder from six cultivars belonging to four different species grown in Guadeloupe (French West Indies): Grande Savane and Jano (D. rotundata), Pas possible (D. esculenta), Adon (D. bulbifera), Caribinra and Goana (D. alata). The Jano and Caribinra cultivars are new hybrids which were developed by INRAE (National Research Institute for Agriculture, Food and Environment) for their resistance to fungal diseases. An optimized extraction process and a new saponin analysis method were developed and validated using negative mode ion trap UHPLC-MS. Compounds were identified by comparing them to commercial standards and to the molar masses of steroidal saponins already identified in yams. Total variance in saponin content was mainly explained by cultivar (Chi²>62.9; p<0.001) and species (Chi²>52.7; p<0.001). The species D. rotundata had the highest concentration of saponins with 843 mg/kg of yam pulp for Jano and 463 mg/kg for Grande Savane. Pas possible contained 361 mg/kg, Adon 18.6 mg/kg and D. alata had the lowest concentrations with 2.8 mg/kg for Goana and 1.6 mg/kg for Caribinra. Cooking in boiling water showed significant differences in saponin content for only two of the cultivars' minority saponins (Chi² mean = 7.92; p<0.001), indicating that the yam cooking method traditionally used in the West Indies does not destroy saponins.
Keywords: yams, cultivars, saponins, UHPLC-DAD-MS, dioscin, optimized extraction, health benefits
