Conclusion and Outlook
The world-wide growing demand for natural flavors poses a chance for
enzyme-based production processes to be implemented to specialty and
fine chemicals industry. In vitro multi-enzyme cascade reactions
are a promising part of such novel, enzyme-based approaches, in that
they present a chance for process integration. Within our research
group, a three-enzyme cascade reaction sequence with integrated cofactor
regeneration and integrated intermediate extraction in a two-phase
system has been successfully established and scaled up for application
in a miniplant at the example of the ester cinnamyl cinnamate. Due to
their high complexity compared to conventional chemical synthesis
routes, however, such enzyme-based processes are difficult to
mathematically describe. On the other hand, mathematical modeling is an
important prerequisite for the industrial application of novel
production processes.
Therefore, in this contribution the authors introduce an Aspen Custom
Modeler® - implemented mathematical model to describe
the aforementioned complex biotechnological production process for a
miniplant-scale reactor setup. Here, sub-models for each thermodynamic
phase and for the integrated extraction step respectively are connected
through differential mass balance equations, resulting in one holistic
mathematical model describing the cascade reaction. In this study,
successful validation of the model with independent experimental data
obtained from the miniplant is presented for the first time. Using this
validated model, multi-objective mathematical optimization runs were
performed with the in-house-developed optimization tool Adv:PO. As a
result, the authors can now identify optimal process operating windows
for any given multi-objective function within the cascade reaction. The
Pareto-optimal dependency of cofactor concentration on cinnamyl
cinnamate space-time yield is analyzed and shown in this work as a
representative example for such optimization results, obtaining a
suitable cofactor concentration range of 1.4 mmol/l to 4.2 mmol/l.
Future research will now further investigate the optimal operating
settings for the miniplant-scale production process. Specifically,
integration of the product separation step will be the focus of our
work: promising results for cinnamyl cinnamate separation from the
product mixture were already achieved using annular chromatography.
Incorporating the downstream process into the mathematical model for
process optimization will show the full potential of this novel process
specifically, and the benefits of applying mathematical modeling and
optimization to biotechnology in general.