Assessment of antinutritional factors and bioavailability of calcium and zinc in wild yam (Dioscorea spp.) tubers of Nepal

The purpose of this study was to determine the antinutritional factors in four wild yam species (Dioscorea bulbifera, D. deltoidea, D. versicolor and D. triphylla) of Nepal. The ranges of antinutrient contents were found to be: oxalates (Ox) 67–197 mg/100 g fresh weight (FW), phytate (Phy) 184–363 mg/100 g dry matter (DM), cyanogens 3.2–6.0 mg of HCN/kg FW, trypsin inhibitor activity 4.1–20.9 mg of pure trypsin inhibited/g DM, and α-amylase inhibitory activity 78-147 IU/g DM. The ranges of Ox:Ca, Phy:Zn, Ca:Phy and [Ca] [Phy]/[Zn] molar ratios for yam tubers studied were: 1.1–2.2, 10.4–32.3, 5.0–14.1 and 0.27–1.9, respectively. The molar ratios indicated that the bioavailability of Ca and Zn in these tubers could be low. In general, the results tend to imply that the Nepalese wild yams may present a health-hazard potential, which in turn demands proper processing before consumption to eliminate the effects of the antinutrients.