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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.

Mineral lubricating oils are widely used in various industrial sectors for their applications in maintenance and functioning of machineries. However, indiscriminate dumping of these used oils has resulted in polluting the natural reservoirs which subsequently destroys ecological balance. Bacteria can emulsify or lower surface tension between phases of immiscible substrates and can acquire them as their carbon and energy sources. Such a phenomenon is mediated by synthesis of extracellular polymeric substances which can function as eminent surface active compounds based on their surfactant or emulsifying nature. The comparison between bacterial strains (Gram-positive Bacillus stratosphericus A15 and Gram-negative Ochrobactrum pseudintermedium C1) on utilisation of pure straight chain hydrocarbons, waste mineral lubricating oils as sole carbon source and chemical characterization of the synthesized surface active compounds is studied. Characterization analysis by Ultraviolet Visible spectrophotometry, Fourier-transform infrared spectroscopy, Nuclear Magnetic Resonance spectroscopy, Carbon-Hydrogen-Nitrogen analysis has given detailed structural elucidation of surface active compounds. The contrasting nature of bacterial strains in utilisation of different hydrocarbons of spindle oil was observed in Gas Chromatography-Mass Spectroscopy. The variation between both strains in utilisation of hydrocarbons can be manifested in a difference in chemical structure and properties of the synthesized surface active compounds. Scanning Electron Microscopy gives detailed insight into the difference in morphological nature of the compounds. The utilisation of these lubricating oils can address waste disposal problem and offer an economical feasible approach for bacterial synthesis of surface active compounds. Additionally, their distinctive nature and properties can maneuver applications in bioremediation of toxic environmental pollutants and as biomaterials in pharmaceutics.