Biochemical Changes in Micro-Fungi Fermented Cassava Flour Produced from Low- and Medium-Cyanide Variety of Cassava Tubers

Abstract

Comparative studies were carried out on the ability of pure strain of Rhizopus oryzae and Saccharomyces cerevisae to alter the nutritional quality of cassava flour produced from low-and medium-cyanide variety of cassava tuber. Low- and medium-cyanide variety of cassava tubers were collected from International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. These tubers were washed, peeled, grated and aseptically inoculated with pure strains of Rhizopus oryzae and Saccharomyce cerevisae in nutrient solution respectively, before allowing them to ferment aerobically for 3 days. The fermented mash was subsequently dried and milled into cassava flour. Subsequently, the proximate, mineral and the antinutrinet composition of the cassava flour were determined. The results of the study revealed that the unfermented flour from low-cyanide cassava variety had higher protein, fibre, ash, fat, Ca, Na and K; while those produced from medium-cyanide variety, had higher antinutrinet (tannin, cyanide & phytate), Zn, Mg and Fe content. However, solid substrate fermentation of the cassava mash using Rhizopus oryzae and Saccharomyces cerevisae respectively caused a significant (P<0.05) increase in the protein and fat content. The nutrient enrichment was significantly higher (P<0.05) in flour produced from low-cyanide cassava variety. In addition, Saccharomyces cerevisae fermentation brought about a higher increase in the nutrient content than Rhizopus oryzae fermentation. Conversely, fermentation of the cassava caused a significant decrease (P<0.05) in the antinutrient content of the flour; although, the level of decrease was more in the flour produced from low-cyanide variety than medium-cyanide variety. Nevertheless, there was no significant difference (P>0.05) in the ability of the fungi to decrease the antinutrient (except phytate) of the cassava flour. Furthermore, micro-fungi fermentation did not cause a significant change (P<0.05) in mineral content (except Mg and K) of the fermented cassava flour. In conclusion, unfermented cassava flour produced from low-cyanide cassava tubers had high nutrient composition and low antinutrient content and more susceptible to micro-fungi nutrient enrichment and detoxification than medium-cyanide variety. Furthermore, Saccharomyces cerevisae was more efficient in the nutrient enrichment of the cassava flour than Rhizopus oryzae.