ELIMINATING CYANOGENS FROM CASSAVA THROUGH PROCESSING: TECHNOLOGY AND TRADITION.

The various traditional methods used for the removal of cyanogens from cassava in Latin America, Africa and Asia were reviewed from the mechanistic point of view. These methods lead to the hydrolysis of the glucosides to give hydrocyanic acid which is either volatilized or leached out through dissolution in water.

Grating was found to be very effective through bringing the enzyme and the substrate together intimately. Fermentation of cassava roots by soaking which is very popular in Africa is one of the most effective techniques for cyanogen removal, and when this is followed by drying, especially sundrying, it is possible to obtain a cyanogen-free product.

The hydrolysis by the endogenous linamarase enzyme is a reversible reaction facilitated by the growth of microorganisms that subsequently results in the gradual decrease of the pH of the medium from about 6.0 to 3.8. At the initial high pH values the forward reaction is favored, but as the pH decreases hydrolysis is impeded due to the fact that the reverse reaction is favored. Hence with most methods involving hydrolysis, unless it is combined with other methods it could be extremely difficult to eliminate all the cyanogens. Because of this, boiling, frying, cooking and drying directly are inefficient methods. Traditional methods always tend to combine one or two of the efficient methods with the other less efficient ones to give an almost cyanogen-free product.

Some of these traditional methods which originally depended on the culture, availability of water and cassava variety have now been modified to give a greater mechanical advantage, for example, the use of hydraulic jacks instead of stones for dewatering, belt-driven roller systems for grating instead of flat tins with holes.