Effect of variety and plant age on the cyanide content of whole-root cassava chips and its reduction by sun-drying

Abstract

The cyanide content of fresh whole-root chips of two cassava varieties (CMC-40, low-cyanide, and CMC-84, high-cyanide) as affected by plant age (9–12 months) was determined monthly, as was the effect of sun-drying, either on concrete floors (plain or black-painted) or on inclined trays, on cyanide elimination. Total cyanide contents in fresh chips of variety CMC-84 were always higher (772 ± 167 vs. 436 ± 111 mg/kg DM) than those of variety CMC-40, and in both varieties cyanide contents in chips decreased as plant age increased. Most of the cyanide in fresh chips was found as bound cyanide (66% for CMC-40 and 79% for CMC-84), but the proportion of free cyanide was higher than values previously determined in the separate root tissues. Sun-drying on inclined trays normally required less time than on a concrete floor; at the fresh chip loading rate used (8.5–9.0 kg m −2) for floor drying, no appreciable differences in drying times and cyanide elimination were found between plain and black-painted concrete surfaces. Sun-drying on a concrete floor eliminated more cyanide (86–93% of initial level), for both varieties, than on inclined trays (61–87%). Most of the remaining cyanide in chips dried on a concrete floor was found as free cyanide (62 ± 16% for CMC-40 and 59 ± 18% for CMC-84), but in chips dried on trays these values were considerably lower (25 ± 11% for CMC-40 and 19 ± 8% for CMC-84). Results are discussed in relation to the maximum hydrocyanic acid concentration (100 mg kg −1) that has been set as a quality standard for cassava chips or pellets.