Production of gluconic acid by fungal species isolated from soil in Keffi, Nigeria

This investigation aimed at production of gluconic acid by fungal species isolated from soil in Keffi. Standard microbiological methods were employed for isolation and identification of the fungal isolates. The yields of gluconic acid produced by the different isolates of the fungi were determined using gas chromatograph and mass Spectrometry. The occurrence of fungi showed that Rhizopus oryzae was 100%, Aspergillus carneus was 75.0%, Aspergillus niger was 75.0% and Aspergillus terreus was 100% while Trichoderma viride was 25.0% and Fusarium moniliforme was 25.0%. The result further demonstrated that three species of the fungal isolates Aspergillus niger, Aspergillus carneus and Fusarium moniliforme were found to produce gluconic acid. Screening for gluconic acid production showed that Aspergillus carneus isolated from locations As1, Cs1 and Cs2, Aspergillus niger isolated from locations Bs1, Bs2 and Cs4 were able to produce gluconic acid. Result of effect of temperature, pH, substrate concentration and fermentation time on production of gluconic acid showed that Aspergillus niger Bs2 produced highest amount of gluconic acid at 28oC, similarly highest amount for gluconic acid produced by Aspergillus carneus As1 was at 28oC, whereas Fusarium moniliforme Bs4 produced highest at 30OC. pH 6.5 was found to the best optima pH for production of both gluconic acid for the fungi studied namely Aspergillus niger Bs2 and Aspergillus carneus As1 and Fusarium moniliforme Bs4 produced highest gluconic acid at pH 5.5. The substrate concentration showed highest production of gluconic acid was produced by Aspergillus niger Bs2 at substrate concentration of 25%. Aspergillus carneus As1 produced highest at substrate concentration of 20% and Fusarium moniliforme Bs4 produced highest at substrate concentration of 20%. The fermentation time showed highest production of gluconic acid by Aspergillus niger Bs2 and Aspergillus carneus As1 was after 144 hours whereas F. moniliforme Bs4 produced gluconic acid after 120hrs respectively. The fungi species isolated from soil in keffi revealed great ability in production of gluconic acid.