4. "Factors regulating production of glucose oxidase by Aspergillus niger".
D. G. Hatzinikolaou and B. J. Macris.
Enzyme and Microbial Technology, vol. 17, pages 530–534, (1995).   View at publisher's site   Request copy
Abstract: Certain factors affecting production of extracellular and cell-bound glucose oxidase by Aspergillus niger were investigated. The intention was to maximize total glucose oxidase activity of academic and potential commercial application by the selection of the appropriate strain and consecutive optimization of growth media and conditions. It was possible to identify combinations resulting in the utilization of molasses as the best carbon source and enhancing enzyme activity approximately 40-fold. Glucose oxidase activities as high as 5.7 U^.ml⁻¹ were produced, comparing favorably with those reported for other enzyme-producing microorganisms. These activity levels were obtained with molasses, indicating an economically attractive process for enzyme production. In addition, our work identified CaCO₃ as a particularly strong inducer of glucose oxidase activity.

3. "Optimizing Multienzyme Production".
D. G. Hatzinikolaou and B. J. Macris.
Annals of the New York Academy of Sciences, vol. 672, pages 595–602, (1992).   View at publisher's site   Request copy
Abstract: The possibility of optimizing certain fermentation conditions towards the total unit productivity of several enzymes has been investigated. As a model system, we used a particular strain of Aspergillus niger capable of simultaneously producing significant levels of superoxide dismutase, glucose oxidase and catalase. The fermentation parameters used in the optimization were the fermentation time, and the concentration of carbon and nitrogen source. The optimum set of fermentation parameters for maximum production of each enzyme has initially been determined. The introduction of a value factor for each enzyme unit of specific purity, yields to the conclusion that there is a point in the parameter space, different from that of optimum production for each separate enzyme, where a maximum exists for the total unit value of the three enzymes produced. This result suggests that multi-enzyme optimization in fermentations may effectively reduce the cost of the production process.

2. "Extractive Fermentation Systems for Organic Acids Production".
D. G. Hatzinikolaou and H. Y. Wang.
Canadian Journal of Chemical Engineering, vol. 70, pages 543-552, (1992).   View at publisher's site   Request copy
Abstract: Basic characteristics of on-line extractive fermentation of organic acids were examined using a general model for the integrated process in order to illustrate the effects of various process parameters and operational modes on system performance. The strong pH dependence of both the fermentation kinetics and the extraction efficiency has been outlined and taken into account by inclusion of a model equation which predicts the pH profile. Simulation results using data from butyric acid fermentations show that our complete model system is adequate to evaluate different operational modes of the process, including simple batch fermentation, batch or fed-batch fermentation with extractive recycle, and continuous fermentation with extractive recycle. In the case where a second undesired acidic byproduct is also produced, our model predictions suggest that on-line extractive fermentation using a suitable solvent results in an effective gross separation of the two acids.

1. "Quantitative Evaluation of the pH Profile in Organic Acid Fermentations".
D. G. Hatzinikolaou and H. Y. Wang.
Biotechnology and Bioengineering, vol. 37, pages 190-195, (1991).   View at publisher's site   Request copy
Abstract: One of the most important considerations in designing an integrated process for the production of organic acids is the strong pH dependence of the process parameters. The release of the acidic products during the fermentation alters the pH of the broth and subsequently affects the kinetics of cell growth and product formation. In addition, some parameters (such as the distribution coefficient of the products during extraction, their solubility constants during precipitation, etc.) in the subsequent separation processes following fermentation are also strong functions of pH. A pH profile predicting model for organic acids fermentation could be used in combination with specific separation process equations, in order to perform simulations concerning the feasibility of the whole process or the evaluation of the system's performance. In this work, such a general pH profile predicting model has been developed. The model requires knowledge of the fermentation medium composition and the kinetics of cell growth and product formation. The model has been verified for (but by no means restricted to) the case of butyric acid fermentation.