Effect of Harvesting Damages on Cyanide Levels in Different Tuber Zones of Two Commonly Cultivated Cassava Varieties in Mapalana, Sri Lanka

Abstract

Cassava is one of the staple foods consumed in developing countries. However, it contains cyanogenic glucoside which turns into toxic compound hydrogen cyanide (HCN) when damaged to the cells of cassava tubers. HCN levels of damaged and undamaged locally grown cassava varieties (MU 51 and Kirikawadi) were determined during harvesting using the titrimetric method. The results showed that the HCN level of undamaged MU 51 (14.69 ± 1.69 mgkg-1) was significantly higher (p<0.05) than that of the undamaged Kirikawadi (12.46 ± 0.58 mgkg-1) variety. The HCN level of damaged MU 51 (18.18 ± 2.83 mgkg-1) was also significantly higher (p<0.05) than the damaged Kirikawadi variety (15.07 ± 3.26 mgkg-1). Moreover, the HCN levels of both varieties were lower than the recommended safe limit of 50 mg HCN by Codex Alimentarius Commission. Further, it was found that the HCN levels of damaged tubers were significantly (p<0.05) higher than that of undamaged tubers of both varieties. The tuber cortex contained higher HCN levels followed by the parenchyma and pith. In addition, the proximal part (close to stem) of the tuber contained higher HCN levels compared to central and distal parts. However, radial HCN levels from cortex to pith showed a sharp negative gradient than the longitudinal HCN level from proximal to distal part of both cassava varieties. Further, HCN levels of damaged sites were found to be high and showed a reducing gradient from the damaged end of both varieties. Therefore, damaged cassava tubers can be consumed after removing peripheral parts at least up to 5 cm from the damaged end.