An Experimental Design Approach for Determining Optimum Nutrient Medium Composition for Citric Acid Production from Pineapple Peels

Abstract

In this study, citric acid was produced from pineapple peels via solid state fermentation using Aspergillus niger and the optimum composition of the medium consisting of magnesium sulphate (MgSO4.7H2O) and potassium dihydrogen phosphate (KH2PO4) was determined using statistically designed experiments. Potassium ferrocyanide (K4Fe(CN)6) and ammonium oxalate ((NH4)2C2O4) were used to reduce the effect of inhibitory metals such as calcium, iron, zinc, copper and magnesium. A four variable Box-Behnken design (BBD) coupled with response surface methodology (RSM) was adopted to develop a statistical model for obtaining the maximum citric acid concentration as well as the optimum levels of the medium components. The results obtained revealed that the model was statistically significant (p<0.0001) with a low standard deviation (0.29) and did not show lack of fit (R2=0.996). Furthermore, all the medium components apart from magnesium sulphate had an overall positive effect on citric acid production. These effects were determined to be statistically significant (p<0.0001). Statistical optimization of the medium composition revealed that maximum citric acid production (36 g/l) was obtained at levels of 2.0 g/l (K4Fe(CN)6), 25 g/l ((NH4)2C2O4), 0.20 g/l (MgSO4.7H2O) and 2.26 g/l (KH2PO4). Results of validation experiments carried out showed that the optimum conditions obtained were similar to those predicted by the statistical model.