Cooking effects on oxalate, phytate, trypsin and α-amylase inhibitors of wild yam tubers of Nepal

Wild yams (Dioscorea spp.) are widely consumed and hold important place in the diet of local people of Nepal. The objective of this work was to investigate on the effect of different domestic cooking methods on antinutrients, such as oxalate (Ox), phytate (Phy), trypsin inhibitor activity (TIA) and α-amylase enzyme inhibitor activity (AIA), contents in these wild tubers. Four yam varieties (D. bulbifera, D. versicolor, D. deltoidea and D. triphylla), available in mid-central region of Nepal, were studied. The effect of three domestic cooking (boiling, pressure cooking and baking) on Ox, Phy, TIA and AIA was determined on raw and cooked samples. The different cooking methods studied showed considerable extent of deviation of antinutrients from the uncooked condition. The average reduction ranges on cooking were 10–45, 5–20, 90–95 and 10–25%, for Ox, Phy, TIA, and AIA, respectively. Cooking showed considerable reduction in TIA and OX, but Phy and AIA were fairly affected. The reduction of antinutrients on cooking is expected to enhance nutritional value of these wild tubers. The antinutritional factors, though showing a high concentration in raw tubers, should not pose a problem in human consumption if the tubers are properly processed.