STATISTICAL DESIGN AND OPTIMIZATION OF METAL ION CONCENTRATIONS FOR SUBMERGED FERMENTATION OF CITRIC ACIDAuthor(s): K. ANAND KISHORE and G. VENKAT REDDY
The present investigation reports the statistical design and optimization of metal ions involved in the submerged fermentation of citric acid by Aspergillus Niger NCIM 705. Citric acid is one of the bulk chemicals synthesized by fermentation. The supply of natural citric acid is limited and hence the demand can be satisfied by fermentation processes. Since recent times, Aspergillus Niger is predominantly employed for large scale production of citric acid. The optimization of fermentation conditions has got lot of impact on the economy of the process. The study on interactions of different physical and chemical parameters of fermentation will permit satisfactory modelling and optimization of the process. Copper (Cu2+), zinc (Zn2+) and magnesium (Mg2+) are identified as the important metal ions in the biosynthesis of citric acid using Aspergillus Niger. Experiments conducted for investigating the effects of the ions in the form of CuSO4.5H2O, ZnSO4.7H2O and MgSO4.5H2O on the yields of citric acid are designed by Central Composite Design (CCD), one of the methods of Response Surface Methodology (RSM). The statistical Design-Expert software was used to generate a regression model to predict the combined effect of ions yield of citric acid. A second-order polynomial equation was fitted to the experimental data to construct the response surface model using multiple regressions. The response of ions was predicted by the polynomial equation. With the citric acid production values computed using polynomial equation, the significance of effect of each ion was analyzed using Analysis of variance (ANOVA). It was observed that copper and zinc ions showed good effect on citric acid production whereas magnesium had no impact. With the citric acid production values predicted by CCD second order equation, three-dimensional response surface curves were obtained using RSM. From the studies, 59.592 mg/L of maximum citric acid was fiund to be produced at the optimum ion concentrations of copper: 1.47 mg/L, zinc: 2.46 mg/L and magnesium : 1.25 mg/L.