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Abstract

Citric acid (2-hydroxy propane 1, 2, 3-tricarboxylic acid) is among the topmost important natural and generally regarded as safe (GRAS) organic acid. It has widespread use in various industries. Several microorganisms have been used to produce citric acid but Aspergillus niger has lingered as the primary choice for commercial citric production by submerged fermentation technique. A total of 14 fungal cultures were isolated from various sources via spread plate method. Among all the isolates, 20% were screened as citric acid producer, whereas a fungal isolate Aspergillus niger RAM 7 was recognized as the potent producer of citric acid that showed the large yellow halo on bromo cresol purple media and was selected for further experimentation. The strain RAM 7 showed 25% (96 h) production of citric acid in the sucrose-based medium that reached up to 55.36% after 168 hrs (6 days) of cultivation under submerged fermentation. To make the process economical twelve discarded starchy substrates such as banana peels, potato peels, sugarcane bagasse etc. were selected and incorporated in the fermentation media. Amongst all the agro waste, the A. Niger RAM 7 was found capable of producing 48.64% of citric acid within 144 hrs in the presence Grapefruit peel. The effect of several physical and chemical parameters on production of citric acid was examined. The maximum production of citric acid was observed at 144hrs. of incubation time, Temperature at 30℃ (53.67%), pH of 5 (53.12%), 5% of grapefruit peels concentration (50.24%), carbon source as Sucrose (51.24%), nitrogen source as Ammonium Nitrate (NH4NO3) (51.84%), 5% inoculum size (54.4%) and by utilizing 48 hrs. old inoculum (55.04%). Further the citric acid has been purified by the method of precipitation which yields 0.434 g of citric acid from 350ml of filter broth. Later, produced citric acid was estimated by TLC having Rf value of 0.72. Finally, the qualitative tests have been performed for citric acid confirmation.

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