Abstract
Objective: The present study aimed to evaluate dried pomegranate peels as a substrate for citric acid production by Aspergillus niger.
 Methods: The morphological study of Aspergillus niger was carried out by wet mount with lactophenol cotton blue and slide culture method. A preliminary qualitative screening of citric acid-producing ability of this fungal strain was also performed by using the Czapek-Dox agar medium containing Bromocresol green. Dried and finely powdered Pomegranate peel was used as a principal substrate for the production of citric acid by submerged fermentation. Classical method of citric acid recovery involved a precipitation technique using calcium hydroxide followed by filtration and subsequent treatment with sulphuric acid. The citric acid produced was also chemically detected and titrimetrically estimated by 0.1 N NaOH.
 Results: The present experiment demonstrated that pomegranate peels may serve as an inexpensive medium for the production of citric acid with a yield of 19.39 g/l by using Aspergillus niger.
 Conclusion: This study provided an alternative basis to recycle the fruit peel waste of pomegranate in order to achieve industrially feasible and environmentally sustainable bio-production of pharmaceutically significant citric acid.
Highlights
Citric acid is considered as one of the important organic acids that have a wide commercialization potential
Aspergillus niger provided by the Microbiology department of the Institute of Genetic Engineering was subcultured on PDA medium
The mycelial growth of Aspergillus niger was studied after growing in PDA media, by mounting with lactophenol cotton blue stain, which effectively stains the chitin of the fungal cell wall
Summary
Citric acid is considered as one of the important organic acids that have a wide commercialization potential. Currie in 1917 performed pioneering work on citric acid production. Citric acid is used in the food and beverage industry to flavour fruit juices, candy ice cream etc. Citric acid is used as an acidulant in mild astringent formulations, in rapid dissolution of active ingredients, as an anticoagulant, effervescent in powders and tablets in combination with bicarbonates, solubilization action for cathartics, antioxidant in vitamin preparations, metallic-ion chelator and buffering agent, as an antioxidant and cosmetic preparation. Major production of citric acid was conducted via microbial fermentation, as it was economical and easy to handle. The demand for citric acid is increasing faster than its production and more economical processes are required [4]
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