Abstract
In microbial cultivations there is a great need for online biomass determination, especially in such cases, where classical methods have limitations. Capacitance-based sensors are developed and widely used in stem cell and other cell cultures [1, 2]. In the present study we have tried to apply such a capacitance-based online biomass determination (Incyte, Hamilton AG) for many microorganisms of different types. Since the signal of this sensor is dependent on the polarizability of the measured cells, the applicability of the sensor should be checked for every species. Thus, we developed a method as a preliminary sensor application test which is faster and simpler than testing this sensor directly in real cultivations. We have tested an Incyte sensor with prokaryotic species (Lactobacillus sp., Clostridium) and eucaryotic strains (Saccharomyces cerevisiae, Cryptococcus albidus, Rhizopus oryzae, Chlorella vulgaris, Nannochloropsis oculata). Furthermore, according to our best knowledge this is the first report of a capacitance sensor application for microalgae. Finally, via conductivity measurements of the same sensor, we could even follow product formation in some cases too.
Highlights
The monitoring of microorganism concentration is one of the key tasks during fermentations and one of the biggest challenges too
We have developed a rapid experimental method, which can be applied without running long fermentations, and which support decision, whether the given strain in the suggested media is able to reach as high a concentration as required by the sensor for the successful determination of online viable cell counts (OVCC) or not
3 Results In some real microbial fermentations the final biomass concentration we detected was too low, and one could conclude that the sensor is inappropriate for those cultures
Summary
The monitoring of microorganism concentration is one of the key tasks during fermentations and one of the biggest challenges too. Because of the discrete character of the measured data, for kinetic evaluation purposes (i.e. determination of specific growth rate, production rate etc.) the fitting of continuous functions to the data points was necessary via non-linear regression [3]. These transformations can be avoided if nearly continuous measurements are possible, for which on-line sensors can play an important role. Process Analytical Technology (PAT) is more often used as a tool to achieve the Quality by Design (QbD) principle [4, 5] These require fast online measurements, especially in terms of biomass. Control of the fermentation requires rapid and reliable determination of the viable cell count
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