Application of Box-Behnken Design for Optimum Citric Acid Production from Cocoyam Starch Hydrolysate using Aspergillus niger

Abstract

This study investigated the use of design of experiment (DOE) for response surface methodology (RSM) to analyse and optimise the production of citric acid from cocoyam starch hydrolysate. The effect of three factors, temperature, pH and inoculum density on citric acid production was determined using a three variable Box-Behnken design (BBD). The BBD was used to develop a statistical model to describe the production of citric acid and the fermentation conditions were then optimised using RSM. The model was statistically significant (p<0.0001) with a low standard deviation (0.52) and did not show lack of fit (R²=0.997). Citric acid production was favoured by intermediate levels of temperature, high levels of pH and low levels of inoculum density. The initial pH positively influenced citric acid production while the reverse was the case for inoculum density. The optimum values of temperature, pH and inoculum density were 32.98 ^oC, 8.0 and 0.5×10⁶ spores/mL respectively. Under these conditions, the citric acid concentration was obtained as 26.2 g/L. Validation of the statistical model showed no significant difference between experimental and model predicted results.

Keywords: Citric acid, Submerged fermentation, Box-Behnken design, Optimisation, ANOVA