Figure 5. Pareto front of a multi-objective optimization of product flow and cofactor concentration in the cascade reaction sequence with varying generation number.
The optimal values shown in figure 5 vary from 1.3 mmol/l to 9.8 mmol/l for cofactor concentration and 0.49 mmol/(l∙h) to 2.84 mmol/(l∙h) for CCI space-time yield respectively. Moreover, our results identified a suitable operating window, as the CCI space-time yield rate significantly increases with a higher cofactor concentration. This remains true up to a value of approximately 4.2 mmol/l, after which the space-time yield difference is smaller than 1 % with increasing cofactor concentration. The lower operating window frame can be set according to a usual space-time yield value of 1 mmol/(l∙h) for industrial biotechnological processes and to a corresponding cofactor concentration of 1.4 mmol/l, thereby framing the most promising operating window with regard to the aforementioned two objectives.
Such optimization runs can now be performed for multiple experimental conditions and objectives, allowing for a profound understanding of the multi-enzyme cascade reaction sequence and the production process of CCI in the miniplant without the need for cost- and time-intensive experiments. To the best of our knowledge, multi-objective mathematical process optimization has not yet been applied to complex multi-enzyme cascade reactions in a miniplant-scale reactor setup.