Cyanogenic glycosides and cassava processing: a review and comparative analysis of different processing approaches on the safety and quality of high quality cassava flour

Abstract

Cassava is one of the most important root and tuber crops, providing nourishment for more than half a billion people the world over. It derives its importance from the fact that it is a valuable source of less costly calories, widespread and an integral contributor to food security in developing countries. The crop has received attention as a raw material for a wide range of industrial applications including the production of bioethanol, adhesives, pharmaceuticals, plastics as well as pelletized animal feed. One of the drawbacks of the root crop for use as food is its potential toxicity, a phenomenon which stems from the cyanogenic glycoside content of the crop. These compounds undergo enzymatic degradation to produce HCN which is lethal at 35 - 150 μmol/kg. Sub-fatal doses over a long period affect the nervous system and thyroid glands. Cyanogenic compounds also account for bitterness in certain cassava varieties. Detoxifying cassava presents an avenue for expanding its domestic and industrial potential as a raw material. These techniques involve a combination of unit operations that trigger the by endogenous enzymes into HCN, which is subsequently evaporated (by heating) or dissolved in water (depending on the processing method under consideration). Processing breaks down cyanogens markedly and reduces their potency. This, however, depends on the starting material and the method and extent of processing. Recent attempts at making cassava a more useful as a raw material for industrial applications has been to process into unfermented High Quality Cassava Flour (HQCF). This flour is useful for bakery products, production of glucose syrup and starch but its safety and quality are not streamlined because of the different approaches adopted in its processing. In this study, the effect of different processing techniques on some safety and quality parameters were evaluated. Two size reduction methods (grating and slicing) and two drying methods (mechanical and solar drying) used to process cassava into flour were compared