PROCESSING OF CASSAVA ROOTS IN BRAZIL: SAFETY IMPLICATIONS

Cassava is widely used in Brazil, in homes and industries, resulting in a variety of food products (Figure 1). Sweet and bitter cultivars are produced by small holders for culinary purposes. On plantations, which are mainly in the south of Brazil, only bitter ones are produced; this is for industrial use. Sweet and bitter cultivars are related with, respectively, low and high cyanogen levels.

In the food industry, cyanogen level reduction is achieved by heating and drying, whilst traditional processing relies on fermentation processes. All processed cassava foods used in Brazil, like farinha d'água, carimã, puba, farofo, tupicupi and starch, are safe in relation with cyanide toxicity. Sun- or artificially dried chips can retain some residual cyanogens. The chips are used for animal feed or as a raw material for industrial uses. The traditional form of cooking cassava in Brazil is to cut the peeled roots in big pieces, and to put it in cold water and boiling it. In other types of food, cassava roots are ground, fermented or pressed and the toxic substance is eliminated. If the roots are fried without previous cooking, most of the toxic compounds may remain.

The amount of cassava wastes generated depends on the processing method adopted. Culinary uses do not produce significant amounts of wastes. Waste quality and quantity vary a lot because of many factors, such as plant age, time after harvesting, type and setting of industrial equipment. Industrial processing forms a serious environmental problem. Even the very small factories such as "Casas de farinha", the smallest flour factories, produce significant quantities of residues. Sour or fermented starch factories are concentrated in two districts of Minas Gerais State, and are an example for that. Paranavai, a district from Paraná State has about 150 flour industries of different dimensions. Residues generated can be solid or liquid. The solid wastes are brown peel, inner peel, refuse, crude fiber, bagasse and flour refuse. The liquid waste is root extract, manipueira. The water used on starch extraction dilute manipueira, reducing its organic load and cyanide content, but increasing its volume. Manipueira has a variable composition, mainly in cyanogen content, which depend on the cassava cultivar used. It contains the majority of soluble substances and some insoluble substances in suspension. All residual starch (2 to 10%) should be removed from manipueira before its spilling or treatment. In Santa Catarina State cassava starch industries produce effluents with chemical oxygen demand of about 25,000 mg O₂ per liter, and which correspond to a pollution caused by 460 inhabitants. Several forms of use and treatment of these wastes are studied in the São Paulo State University.