The present study was aimed to isolate and screen the ability of citric acid producing Aspergillus spp from soil. Citric acid is the most important organic acid, used as a natural preservative and conservative. It is also used to add an acidic or sour taste to foods and soft drinks. In this study, fungal samples were isolated from soil samples, using serial dilution agar plating method and the isolates were identified based on their microscopic and morphological characteristics. From the isolates, the dominant fungal species, Aspergillus niger and Aspergillus fumigatus were sub-cultured using Potato Dextrose Agar (PDA) medium and the fungal species were used for citric acid production. The spores were mixed in the fermentative medium for 72 hours at 30±1° C. After incubation, the citric acid content was estimated by titrimetric method. Among the two species, higher citric acid production was shown by Aspergillus niger S-6. Then it was undertaken for optimisation under various pH, temperature, Carbon and Nitrogen sources. In this assay, the maximum production of citric acid was observed in Aspergillus niger S-6 at pH 6.0, temperature 30±1° C, Carbon source Glucose and Nitrogen source Ammonium sulphate.
The aim of the present study was to compare three carbon sources for Citric acid (CA) production by using mutant strain of Aspergillus niger S-6. UV rays at a wavelength of 365 nm were used as the mutagen on a locally isolated Aspergillus niger strain, arbitrarily named as A. niger S-6. The fungus was exposed to 30 minutes of UV irradiation. Cane molasses, pumpkin and sweet potato were taken as the carbon sources for preparation of fermentation media. CA yield was quantitatively estimated by calculating total titrable acidity (TTA) of fermentation media. Mutagenesis with UV radiation led to more than twofold higher CA production in all fermentation media. Sweet potato medium showed higher CA production of 11.84 + 0.13 g% in comparison to cane molasses (11.37 + 0.11 g %) and pumpkin (10.15 + 0.06 g %) Sweet potato.
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