Cassava Processing: Safety and Protein Fortification

Abstract: Cassava (Manihot esculenta Crantz) is an important and cheap source of carbohydrate in tropical regions, particularly in Sub-Sahara Africa. Cassava as a human food is a good source of energy as it has a comparable high energy density of about 610 kJ/100 g fresh root. The crop has growth advantages and production can take place in soil where other crops such as maize, sorghum and sweet potatoes cannot grow. In the region, cassava is used mainly by the farmers themselves as a subsistence crop because the fresh cassava roots have a short shelf-life (1 to 2 days) after harvest. Consequently, the manufacture of cassava-based industrial products may be of interest as a potential way of boosting the economic value of the crop. Producing a valuable, nutritional and safe food from cassava involves certain challenges. Cassava has a poor protein content (1% fresh root weight) and contains cyanogenic glucosides that may cause intoxication. This thesis reports on work aimed at overcoming these negative aspects of cassava. The report begins by describing how cassava can be detoxified through processing. Secondly, we propose a new method to facilitate the control of residual toxic compounds in cassava products, and finally we describe a methodology for protein fortification of cassava products while preserving consumer-perceived textural properties. The cyanogens in cassava are hydrolyzed into volatile free cyanide by allowing contact between the cyanogenic substances localized in the vacuoles of the cells with hydrolyzing enzymes in the cell walls. This can be achieved by damaging the cells mechanically or by fermentation. Studies carried out in Nampula, Mozambique showed that heap fermentation of cassava roots may reduce toxic compounds by up to 96%. Another process used for the removal of toxic compound in cassava roots is shredding of roots, which is also an efficient detoxification method (98% reduction). Assessment of toxic compounds in cassava products is of crucial importance but most existing methodologies have been shown to depend either on analytical equipment or on laborious and slow procedures. In this study, a simple cyanide detection sensor synthesized from Vitamin B12 is proposed. The new reagent detected the cyanide in seconds and has the advantages of being simple and not toxic. If the economic value of cassava is to be increased, industrial production of cassava-based products is essential. In this study we chose to process cassava into the traditional product known as rale (a dry, pre-gelatinized and granulated product). Protein was added to this product to improve its nutritional value. Addition of protein to shredded cassava roots before roasting resulted in hard agglomerates, a feature that is undesirable for the product. Pre-treatment of protein suspension such as heating and reducing the pH changes the microstructure in such a way that a protein-fortified product could be obtained without properties that the consumer perceives as negative.