Salts soaking treatment for improving the textural and functional properties of trifoliate yam (Dioscorea dumetorum) hardened tubers

ABSTRACT:  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.