Optimisation of Media Components using Central Composite Design for Increased Citric Acid production from Yam Peels using Aspergillus niger

In this study, design of experiment (DOE) for response surface methodology (RSM) was used to analyse and optimise the compositions of the nutrient medium (calcium ion, peptone, ethanol and manganese ion) for citric acid production from yam peels via solid state fermentation (SSF) using Aspergillus niger. A four variable, central composite design (CCD) was used to develop a statistical model for the process while RSM was used to optimise it. The results obtained showed that the model was statistically significant (p<0.0001) and displayed a good fit with the experimental observations (R2 = 0.997). Citric acid production was significant at high levels of ethanol and calcium while the reverse was the case for manganese and peptone. The optimum values of ethanol, manganese, calcium and peptone were 7.0% v/v, 1.0 g/l, 0.1 g/l and 0.1 g/l respectively. Under these conditions, the citric acid concentration was obtained as 66 g/l. Validation of the statistical model showed an insignificant difference between experimental and model predicted results.