A contradiction-based Approach for Air Temperature Choice in Thin-layer Drying of Cassava Roots

Abstract

Setting the drying temperature of cassava slices remains up to now a matter of personal decision from authors, varying from an author to another and for the same author, varying from an experiment to another one. The primary aim of this manuscript is to introduce a decision-making instrument for determining the optimal temperature setting during the thin-layer drying process of cassava slices in general, the thin-layer drying process of bitter cassava roots slices in particular. The thermal conditions for drying should be higher than 37 °C to permit the hydrolysis of cyanogenic compounds into hydrogen cyanide (HCN) and it should not be higher than 30 °C to favor the elimination of HCN upon that of water and prevent the denaturation of thermosensitive nutrients in cassava slices. The TRIZ separation in time method provided a set of three steps for solving that problem. First step, in a preliminary action, cassava slices were introduced in water set at 37 °C for 6 h. The HCN was produced and a large quantity eliminated by solubilization. Second step, during that period, a cassava moisture prior compensation was also achieved: cassava slices uptook additional water, favoring the elimination of the residual HCN at a unique drying temperature, without any particular care. Third and last step, cassava slices were then dried at 35 °C, 40 °C and 45 °C, values of the residual HCN content were 7.23 ± 1.30 mg HCN/kg, 6.42 ± 2.4 mg HCN/kg and 8.06 ± 1.1 mg HCN/kg, respectively. All those values are less than 10 mg HCN/kg, the maximum admissible value for human consumption, set by the World Health Organization.

Keywords: Thin-layer drying, Temperature, Physical contradiction, Cassava cyanide, TRIZ