Antinutritional factors changes occurring in trifoliate yam (Dioscorea dumetorum) tubers after harvest

Studies were conducted on the changes in antinutritional factors occurring during the storage of Dioscorea dumetorum (cv. Yellow) yam tubers. The tubers were harvested and stored under prevailing tropical ambient conditions (19–28 °C, 60–85% RH) for 0, 2, 5, 7, 14, 21, 28, 42 and 56 days. The samples were evaluated for total phenols, tannins, phytic acid, α-amylase inhibitors, trypsin inhibitors and oxalates. Results showed that, during storage, total phenols and tannin contents decreased by approximately 22–28% after 56 days of harvest, due to the hardening phenomenon and sprouting. Phytate and α-amylase inhibitor levels declined, respectively, from 690–416 mg/100 g and 1013–659 AIU/g, while oxalates and trypsin inhibitor contents increased during the first week of storage (days 0–7) and, after this period, they started to decrease progressively. Since sprouting of most tubers was observed after 28 days of storage, the results suggest that post-harvest hardening and sprouting influence antinutritional composition of D. dumetorum tubers.