keywords: Glucose, groundnut cake, methanol, orange peel, pawpaw peel, sucrose
Citric acid (CA) is a valuable organic acid used in many pharmaceutical and industrial food products. The increased demand for its use has led to search for yielding fermentable strains of microorganisms to meet up with the demand. This study evaluated the potentials of groundnut cake and soyabeans as nitrogen supplements on production of CA with pawpaw peels (PP) and orange peels (OP) substrates using Aspergillus niger. Isolation of fungal strain from spoilt fruit sample was done with Potato Dextrose Agar. They were screened for CA production on Czapek-Dox Agar (CZA) and identified morphologically. Each substrate was oven dried at 60ºC for 2 h and analyzed for their proximate composition. Glucose and sucrose at 1, 3 and 5% concentrations were added to each of the substrates and inoculated with the isolate. The effect of groundnut cake and soybean flour was studied at 1, 1.5 and 2% in combination with the highest CA producing carbon source. Methanol was further added to the best carbon and nitrogen source to formulate the solid state fermentation (SSF) medium for CA production. Addition of 5% sucrose proved better than 5% glucose on each substrate with a yield of 73.17 g/kg of CA on PP and 41.27 g/kg on OP after fermentation. Similarly, addition of 2% groundnut cake to the media, gave a higher yield (104.36 g/kg) on PP than OP in the presence of 2% methanol. SSF media of PP containing 5% sucrose and 2% groundnut cake proved better for CA production when optimized with methanol.