Optimising the Effect of Stimulants on Citric Acid Production from Cocoyam Starch Using Aspergillus Niger
Additives such as low molecular weight alcohols, trace metals, phytate, lipids etc have been reported to stimulate citric acid production. Hence the objective of this study was to investigate the effect of stimulating the metabolic activity of Aspergillus niger for the purpose of improved citric acid production from cocoyam starch. A three-variable, three-level Box-Behnken design (BBD) was used to develop a statistical model to study the effects of Zinc (II) ion, Iron (III) ion and methanol on the production of citric acid. Response surface methodology (RSM) was used to optimise the effects of these stimulants. The results of analysis of variance (ANOVA) carried out on the model showed that the model was statistically significant (p< 0.0001) and did not show lack of fit (R2=0.997). The results also showed that citric acid production increased when the levels of zinc and methanol were increased. Intermediate levels of iron were required to produce citric acid at optimum levels. Results obtained from RSM showed that the optimum levels of zinc, iron and methanol were 4.5 g/L, 6.87 g/L and 3.0 %v/v respectively. Under these conditions, the maximum citric acid concentration was obtained as 108 g/L. Validation of the model indicated no significant difference between predicted and experimental values.