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.http://dx.doi.org/10.4314/njt.v34i4.

Dynamic Modelling and Simulation of Citric Acid Production from Dilute Acid Hydrolysed Corn Starch Using Aspergillus Niger

The modelling of batch production of citric acid from corn starch hydrolysate using Aspergillus niger ATCC 9142 was carried out in this work. A validated mathematical model was developed to describe the process. Four kinetic models, Monod, Haldane, logistic and hyperbolic for simulating the growth of the Aspergillus niger cells were explored. The validity of the models in terms of predicting the growth of Aspergillus niger cells was determined by fitting each kinetic model to experimental data. Comparison of experimental results to model predicted results revealed that only the hyperbolic model was able to accurately replicate the experimental results. This was evident from the high level of correlation between the experimental and model predicted results. The kinetic parameters for cell growth, substrate consumption and product formation µmax, Yx/s, Yp/x, Ks and Kp as calculated by the hyperbolic model were 0.0130h-1, 0.711g/g, 13.671g/g, 0.001g/L, and 0.257 g/L respectively. Results of simulating the model showed that the production of citric acid was a growth associated process.  Optimum pH, initial sugar concentration and temperature for citric acid production obtained were5.5, 40w/v and 30oC respectively.http://dx.doi.org/10.4314/njt.v33i2.1

Antibacterial Activity of Vernonia amygdalina and Vernonia cinerea Leaf Extracts through Microwave-Assisted Extraction Technique

The occurrence of multi-drug-resistant bacteria has been a great challenge facing public health care in recent times. Therefore, this study investigated the antibacterial activity of extracts from two species of Vernonia (Vernonia amygdalina and Vernonia cinerea) against Bacillus cereus, Enterococcus faecalis, Pseudomonas aeruginosa, and Escherichia coli. The results obtained showed that the tested bacteria were sensitive to extracts from both plant samples in the concentration range of 6 to 30 mg/mL. Higher sensitivities were seen at a concentration of 30 mg/mL. Moreover, the sensitivities were more in the extract from V. amygdalina leaf as compared to V. cinerea leaf extract. In addition, the minimum inhibitory concentration (MIC) showed a higher susceptibility of B. cereus and P. aeruginosa to V. amygdalina and V. cinerea leaves extracts, respectively. The plant extracts exhibited antibacterial effects against the tested organisms with a potential of being used as antibiotics