Evaluation of Cassava Peels as a Substrate for Citric Acid Production by Aspergillus niger in Anambra State

Cassava processing generates large volumes of peels as a byproduct in Anambra State, South East Nigeria, creating disposal challenges while representing a potential low-cost fermentation substrate. This study evaluates cassava peels as a substrate for citric acid production by Aspergillus niger ATCC 16404 using solid-state fermentation. Cassava peels were collected from garri processing centres in Onitsha and prepared by drying, milling, and supplementing with nitrogen and phosphate sources. Fermentation was conducted at moisture contents of 50, 60, and 70 percent, pH levels of 3.5, 4.5, and 5.5, and temperatures of 28, 32, and 36 degrees Celsius, using a central composite design. Citric acid yield was determined by the pentabromoacetone method. The optimum conditions identified were 65 percent moisture, pH 4.5, and 30 degrees Celsius, producing a citric acid yield of 18.7 g per 100g dry substrate after 120 hours. The study also characterised the compositional changes in the substrate during fermentation. The results demonstrate the feasibility of value-added utilisation of cassava peels for biotechnological citric acid production, contributing to both waste management and the domestic supply of a widely used food additive. The study draws on recent literature on solid-state fermentation of agricultural wastes in Nigeria. Findings have implications for the food additive industry and agro-industrial waste management policy in Anambra State. Keywords: citric acid, cassava peels, solid-state fermentation, Aspergillus niger, Anambra State