Citric acid Production from Agricultural Wastes using Aspergillus niger Isolated from some Locations within Kaduna Metropolis, Nigeria

Abstract

This investigation was carried out to assess citric acid production by Aspergillus species isolated in some locations within Kaduna metropolis Nigeria using standard methods. Fungal isolates identified as Aspergillus niger were obtained from samples collected from four (4) different locations.  Isolates were subjected to substrate preference test using local substrates such as wheat straw, rice straw and potato peel powder. Wheat straw supported the highest growth value of 41%. Screening of A. niger isolates for the production of citric acid showed that the isolate from Kawo (Kw) gave the highest yield of citric acid (0.38g/100ml) on basal screening media. Optimization of pH and temperature were carried out and the optimum temperature and pH for citric acid production by isolate Kw was 30^OC (0.65g/100ml) and pH 6.0. The wheat straw treated with 5 N HCl produced a high yield of citric acid with a value of 25.60g/kg while the untreated wheat straw produced a yield of 13.3g/kg. Molecular characterization to confirm the identity of the fungal isolates was carried out by the amplification and sequencing of the 5.8S gene of the ribosomal RNA and the two intergenic spacers ITS1 and ITS2 of the strains. By comparison (BLAST) of Aspergillus niger isolate to reference sequence in the gene bank, a sequence similarity of 99% to 100% of other Aspergillus niger strain was obtained. Various methods of strain improvement techniques could be adopted to increase citric acid production by the A. niger isolates obtained from this study.