Salts Soaking Treatment for Improving the Textural and Functional Properties of Trifoliate Yam ( Dioscorea dumetorum ) Hardened Tubers

Processing of Dioscorea dumetorum hardened tubers into flour could be a means of adding a longer-term value to this tropical plant with a high nutritional potential, but which presents a postharvest hardening problem characterized by a hard-to-cook defect. In an attempt to investigate the changes leading to salts soaking treatment of hardened tubers, the central composite rotatable design for K= 2 was used to study the combined effect of NaCl concentration (0% to 6%) and pH (4 to 10) on tubers cooked hardness, and 6 kanwa alkaline salt concentrations (1:3 (w/v); 0%, 0.2%, 0.5%, 0.8%, 1%, and 1.5%; pH 11.3 +/- 0.2) were used to study the effect of kanwa treatment on tuber cooked hardness and functional properties of resulting flours. The results showed that salts soaking treatment significantly decreased (P</= 0.05) tubers cooked hardness, independently of the solution pH, but could not totally overcome the tubers hardening phenomenon, as a consequence of the multiple mechanisms of D. dumetorum tuber hardening. Nevertheless, kanwa concentrations of 0.8% to 1.5% could be used to tenderize hardened tubers prior to its transformation in flour. Except oil absorption capacity, initial soaking of hardened tubers in kanwa solutions significantly influenced (P</= 0.05) the functional properties of the resulting flours. Water absorption capacity increased with increasing of kanwa concentration while the other properties evaluated (water solubility index, hydrophilic-lipophilic index, bulk density, swelling capacity, least gel-forming concentration) decreased.