Optimization of Cultural Parameters for Cost Effective Production of Kojic Acid by Fungal species Isolated from Soil

Abstract

Two different species of Aspergillus are able to produce kojic acid at higher concentrations under static conditions in the present study. Various physicochemical parameters which influence the production of kojic acid are optimized by means of One-factor-at-a-time method. The other objective of this research is to examine the prospects of using novel substrates like Cassava, Ipomea batatas, Alocasia macrorrhiza tubers and rice bran, wheat bran for the production of value added products like kojic acid. The kojic acid concentration is quantitatively estimated by Bentley’s colorimetric method. It is observed that the maximum yield of kojic acid crystals, 22.5 g/L is obtained with the substrate Cassava and by the isolate Aspergillus flavus. The optimized physicochemical parameters are initial pH - 6.0, Time - 28d, Temperature - 28ºC, Substrate concentration – 100 g/L, Nitrogen source concentration-2 g/L, MgSO4.7H20-0.5 g/L and KH2PO4-2.0 g/L under static conditions. After the fermentation is completed, the fermented broth samples are subjected to crystallization and the isolated kojic acid crystals are examined by Fourier transform infrared spectroscopy and X-ray crystallographic methods. The FTIR spectrum of the sample kojic acid showed bands at functional groups at 3270.8 cm-1, 3179.43 cm-1 (-OH), 2925.17 cm-1, 2854.05 cm-1 (aliphatic-CH), 1660.59 cm-1 (cyclic-C=O), 1611.11 cm-1 (C=C), 1472.61 cm-1 (deformation of-CH2), 1074.04 cm-1 (cyclic C-O-C), 943.58 cm-1, 863.66 cm-1 and 775.65 cm-1 (1,4 α -disubstituted ring). The X-ray diffraction spectrum of the sample is similar to standard sample and reveals seven distinctive peaks appeared at 2θ angles 8º, 19.27º, 21.71º, 27.73º, 31.15º, 36.13º, 39.09º. The result confirms the presence of kojic acid. Antimicrobial activity of kojic acid is tested on some Gram positive and Gram negative bacteria. The culture Escherichia coli and Staphylococcus aureus show equal susceptibility to the antimicrobial compound kojic acid.