EFFECT OF GROUNDNUT CAKE AND SOYA BEANS ON ENHANCED CITRIC ACID PRODUCTION FROM PAWPAW AND ORANGE PEEL BY MUTANTS OF ASPERGILLUS NIGER

This present study was concerned with the biosynthesis of citric acid (CA) with mutant strain of Aspergillus niger using pawpaw and orange peel as substrates by solid state fermentation process. The A. niger strain isolated from spoilt orange was identified, screened for CA production on Czapek-Dox Agar and subjected to mutation by ethidium bromide. The effect of carbon sources, nitrogen sources and substrates were also determined.  Among the mutant strains, A. niger PJ-02 A120 was found to be the best mutant that produced citric acid (65.00±0.58f) after 48 hours in Vogel’s medium. The effects of carbon sources (sucrose and glucose) on CA production from each substrate (orange and pawpaw peel) using mutant A. niger PJ-02 was determined and sucrose, the best carbon source was combined with two the nitrogen sources (groundnut cake and soyabeans) to determine the most suitable supplement for CA production. Groundnut cake enhances the production of citric acid while soyabeans was inhibitory. Citric acid was further produced in pawpaw peel and orange peel medium containing sucrose (5 %) groundnut cake (2 %), methanol (1.5 %) and the mutant strain. The orange peel substrates yielded 112.07g/kg of CA while 107.17g/kg was recorded for pawpaw peel when fermented for 5 days at 30°C. The Production of citric acid with mutant Aspergillus niger proved better with orange peel than pawpaw peel when optimized with alcohol.