Citric Acid Fermentation by Aspergillus niger

Abstract

From twenty soil samples collected, ninety six isolates were identified as Aspergillus niger. All A. niger isolates understudying were varied in their capability to produce citric acid on Czapek-Dox broth medium. Based on the productivity of citric acid in shake flask cultures after 3 days, the highest local A. niger MH368137, was selected for further experiments with the reference strain, A. niger EMCC132. The optimal time incubation for the maximum citric acid production reached statistically 5 days of fermentation. Through series of experiments were designed on various physicochemical fermentation parameters to establish the optimal conditions for citric acid overproduction, it could be summarized as: optimum temperature, 28˚C; initial pH 6.5; inoculums size 3.0×10⁶ spores/ml; shaking culture (100rpm); maltose as a carbon source 40 g/L; peptone as a nitrogen source 3 g/L; Sodium phosphate as phosphorus source; 2% of methanol as enhancer. Through these environmental and nutritional parameters, citric acid production was clearly improved and gave 14 times higher that reached to 13.33 mg/1ml comparing to the original yields 0.907 mg/ ml by Aspergillus niger MH368137 (FQW). When local agricultural wastes and byproducts (pineapple peel, sugarcane bagasse, potato peels; sugarcane molasses and dates molasses) utilized for citric acid production, local strain A. niger MH368137 (FQW) produced highest amount of citric acid, reached up to 256.94 mg/ ml when grew on sugarcane molasses as a sole carbon source