Comparative Production of Citric and Itaconic Acids from Cassava Peels by Aspergillus spp. and the Indigenous Microflora

Abstract

Plant biomass is a major renewable natural resource of the world and represents a major source of renewable organic matter. Cassava peels which constitute a nuisance to the community can be utilized by microorganisms to produce valuable products like organic acid yet they remain unexploited. This study compared the citric acid and itaconic acid production efficiency of Aspergillus spp. and the indigenous microflora in the cassava peels through solid state fermentation. Source-segregated cassava peels were collected from Garri processing factory in Ibadan, Oyo State, Nigeria, washed with distilled water, sun-dried, grounded and analysed for basic physico-chemical properties using standard procedures. The locally isolated fungal strains of A. niger and A. tereus were isolated from the topsoil using the pour plate method. Citric/Itaconic acid producing strain of A. niger and A. tereus were identified by the use of Czepak-Dox Agar. Aspergillus niger fermentation extract, Aspergillus tereus fermentation extract and crude fermentation extract  were obtained from 5 g of cassava peels after 13 day fermentation using acids-producing strain of Aspergillus niger and Aspergillus tereus, respectively and indigenous microflora in the cassava peels. Assay for citric/itaconic acid was carried out using standard methods and amount produced was derived by translation of absorbance values on the standard curve. The concentration of citric acid in the A. niger fermentation extract increased from 0.02 M on Day 1 to 0.05 M on Day 9 and then decreased to 0.04 M while that of A. tereus increased from 0.02 M on Day 1 to 0.04 M on Day 11 and then decreased along the fermentation days due to utilization of the substrate. In the crude fermentation extract, the concentration of acids increased from 0.02 M on Day 1 to 0.06 M on Day 11 and then decreased to 0.05 M. A. niger fermentation had a slightly higher acid production than A. tereus fermentation, however, both were lower than the crude fermentation. Cassava peel wastes could be used to produce resource materials (organic acid) that are of public health importance. Therefore, the cheaply available substrate for fermentation and the low cost of the fermentation process in obtaining the crude fermentation extract using the indigenous microflora potentially makes its use more economically acceptable.