OPTIMIZATION OF SOLID-STATE CULTURE FOR CITRIC ACID PRODUCTION USING SOME LOCAL STARCHY MATERIALS
This study compares the production of citric acid in different starchy materials; cassava flour, corn flour and rice grain. The effect of nutrient supplementation, initial pH and alcohol addition on citric acid production by Aspergillus niger under solid-state culture was studied. The data obtained indicated that the production of citric acid from different starchy materials (cassava flour, corn flour and rice grain) was significant at (P<0.05) level. Better citric acid production (31.5g/kg) was obtained with cassava flour at optimal pH of 5.5 when compared with 17g/kg and 20.5g/kg produced with rice grain and corn flour, respectively. Production of citric acid from these starchy substrates was ranked as follows: cassava flour > corn flour > rice grain. Increase in incubation period at room temperature resulted in the increased citric acid production up to 120 hours. Supplementation with nutrient cocktail with NH4NO3 as nitrogen sources has better yield of citric acid (53.0g/kg). The highest concentration of citric acid was accumulated when methanorl was added in cassava flour with NH4NO3 as nitrogen source (58.5g/kg).