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Mirror mirror: Online monitoring of fermentation processes

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Dagmar Behmer, marketing manager Bruker, examines the online monitoring of fermentation processes using FT-NIR spectroscopy.  

Fermentation, ‘the anaerobic conversion of sugar to carbon dioxide and alcohol’ is commonly associated with producing beer or wine. In the pharmaceutical environment, cell fermentation is used to manufacture a large number of APIs, targeting a wide range of medical indications from anti-cancer drugs to vaccines and many other medications. It is always used, when the synthetic route is very complex and requires significant and time-consuming development stages.

Basis for the synthesis of an active pharmaceutical ingredient (API), like biopharmaceuticals or biologics are GMOs (genetically modified organisms). Under optimal conditions, they are cultivated in a nutrient solution to maximise the cell growth and thus the productivity of the organisms. For an optimal result − and to apply to the strict regulatory requirements in the pharmaceutical industry − it is necessary to measure, control and adjust the parameters, like glucose, lactate, protein content and more during the fermentation process from the start-up media to the final product.

Challenging measurement conditions and how to solve them

Fermentations are initially transparent but become increasingly opaque as the cultivation progresses. The challenging measuring conditions of fermentation processes require smart technical solutions. Neither transmission nor reflection probes are suitable for monitoring the entire process. To provide reproducible measurements even for opaque slurries and emulsions, transflection probes are advised, which combine the benefits of transmission and reflection measurements.

This is becoming clear when looking at the measurement principles of probes (Figure 1). Transmission probes (left) guide the light once through the medium at a given path length - ideal for clear liquids. Reflection probes (right) illuminate the sample and collect the scattered light – ideal for solid samples. Since the fermentation starts as a clear broth and changes over time to a very turbid liquid, neither of these probes will perform well through the complete process of fermentation. A transflection probe (Figure 1, middle) solves this by combining these two options. At the beginning, it behaves like a transmission probe when the light is reflected by the built-in mirror. The more turbid the solution becomes, the more the light is being reflected by the cells.

These probes can usually be adapted to different process conditions, flange types, immersion depths and steel types. Also, FDA-compliant sealings as well as fully autoclavable versions are available. In combination with the advanced measuring modes of modern fourier transform near-infrared (FT-NIR) spectrometers, which can suppress the influence of gas bubbles on the spectra, reliable results can be obtained.

Summary

Cell fermentation processes are today a reliable production method for small molecules and protein-based APIs, allowing pharmaceutical companies to optimise the production process and time to market. FT-NIR spectroscopy can help to tightly control e.g. fed-batch fermentations by monitoring parameters such as:

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