Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 2(9), 5-8, Sept. (2012) Res.J.Chem. Sci. International Science Congress Association 5 Assessment of relative importance of Process variablesin Citric Acid Fermentation by Plackett-Burman design Kola Anand Kishore and Goli Venkat ReddyDepartment of Chemical Engineering, National Institute of Technology, Warangal-506004, AP, INDIAAvailable online at: www.isca.in Received 2nd May 2012, revised 16th May 2012, accepted 6th June 2012Abstract Citric acid fermentation process is controlled by different operating variables: Initial sucrose concentration, Initial pH, Stirrer speed, Incubation time, Fermentation temperature, O2 flow rate, moisture content, particle size, inoculum density, methanol concentration, spore age etc. The present work reports the evaluation of the parameters by Plackett-Burmandesigns, one of the factorial design methods using design expert softwareto screen the strongly influencing variables for their subsequent optimization to improve the citric acid fermentation from Sucrose using Aspergillus Niger NCIM-705. Plackett-Burman is a specialized design for 2 to 31 variables where each variable can be varied over two levels. The lower and upper limits of eleven variables stated above were identified from the literature. The variables with their operational range were processed in Plackett-Burmandesign software until a point where the design matrix evaluation for factorial main effect model was obtained. All trials were performed in triplicate and citric acid yield hs been treated as response variable. The main effect of each variable was calculated as the differencce between the average of measurements made at the high setting(+) and at the low setting(-) of that factor. The six variables; Initial sucrose concentration, initial pH, stirrer speed, incubation time, fermentation temperature and O2 flow rate were found to be the most influencing parameters on the yields of citric acid. Keywords: Citric acid, Aspergillus Niger, fermentation, operating variables, factorial design and plackett-Burman design. IntroductionA variety of carbon sources can be used for citric acid fermentation. Molasses, sucrose or glucose syrups are favored commercially. Citric acid is widely used in the food and beverage industries as an acidifying and flavor-enhancing agent, pharmaceutical industry and elsewhere. The entire worldwide demand for citric acid is met by fermentation mainly by the process involving the filamentous fungus A. niger as it is the most commonly employed organism for citric acid fermentation. For an efficient citric acid production, the growth of Aspergillus in pellet form is desirable and this can be achieved by process optimization. A well defined statitistical experimental design is considered to be necessary for optimization of a fermentation process. The development of the fermentation process has got its impact on the economy and practability of the process. Hence, the optimization of operating conditions has become a challenging task for the researchers in the recent years. The diversity of combinational interactions of physical and chemical fermentation parameters and production do not permit satisfactory detailed modeling. In the present work, we report the optimization procedure for citric acid production by A. niger through response surface methodology, a statistical Optimization method as an effective tool for fermentation engineering. The largest industrial consumers of Citric acid include food, beverage, chemical, pharmaceutical and other industries. The effects of pH, temperature, time of fermentation, sugar concentration, nitrogen concentration and potassium ferrocyanide on citric acid production were investigated using response surface methodology. Regression equations were used to model the fermentation to determine the optimum fermentation conditions. Higher yields were obtained after optimizing media components and conditions of fermentation. Maximum citric acid production was obtained at pH 5.35, 29.76°C, 5.7 days of fermentation with 221.66 g of substrate/l, 0.479 g of ammonium nitrate/l and 2.33 g of potassium ferrocyanide/l. Although many microorganisms can be used to produce citric acid, A. niger remains the main industrial producer. Specific strains that are capable of overproducing citric acid have been developed for various types of fermentation processes. The Plackett-Burmandesigns (PBD) have been widely used for screening process variables that make the significant impact on a process. PBD is a set of small and efficient experimental designs, which is very much reliable, widely applicable and especially well suited for bioresearch and development. Recent reports on the use of PBD include its application toward improving antibiotic, Saccharopolyspora spinosa macrolide, Colletotrichum coccodesspores. Screening studies by PBD considers the ratio of the number of experiments to be conducted to the number of variables being studied. This design allows for the study of k= (N-1)/ (L-1) factors, each with L levels with N experimental trials. The usefulness of the design lies in the fact that in determining the effects of one variable, the net effects of changing other variables cancel out so that the effect of each variable on the system can be independently