Winfried Storhas

On-line carbon balance of yeast fermentations using miniaturized optical sensors.

Monitoring of microbiological processes using optical sensors and spectrometers has gained in importance over the past few years due to its advantage in enabling non-invasive on-line analysis. Near-infrared (NIR) and mid-infrared (MIR) spectrometer set-ups in combination with multivariate calibrations have already been successfully employed for the simultaneous determination of different metabolites in microbiological processes. Photometric sensors, in addition to their low price compared to spectrometer set-ups, have the advantage of being compact and are easy to calibrate and operate. In this work, the detection of ethanol and CO(2) in the exhaust gas during aerobic yeast fermentation was performed by two photometric gas analyzers, and dry yeast biomass was monitored using a fiber optic backscatter set-up. The optical sensors could be easily fitted to the bioreactor and exhibited high robustness during measuring. The ethanol content of the fermentation broth was monitored on-line by measuring the ethanol concentration in the fermentation exhaust and applying a conversion factor. The vapor/liquid equilibrium and the associated conversion factor strongly depend on the process parameter temperature but not on aeration and stirring rate. Dry yeast biomass was determined in-line by a backscattering signal applying a linear calibration. An on-line balance with a recovery rate of 95-97% for carbon was achieved with the use of three optical sensors (two infrared gas analyzers and one fiber optic backscatter set-up).

A Bilinear Hybrid Model for Diauxic Production of ß-Galactosidase by E.coli in Biotechnological Plants

In this paper, a complete dynamical model for a bioprocess in pharmaceutical industry is proposed. The obtained model is bilinear and hybrid. Thus, the process forms a good application example for both, the field of bilinear systems and the field of hybrid systems. It is therefore possible to improve the control system performance by using nonlinear hybrid control techniques. Validation of the model shows satisfying results. In addition, as the model is valid for all fermentation processes and its derivation is performed step-by-step this paper can also serve as introductory example for teaching process modeling.

Advanced In Situ Microscopy for On-Line Monitoring of Animal Cell Culture

Cell concentration is one of the key parameters to be monitored during cell cultivation processes. This is very often done off-line by sterile sampling and subsequent counting using a hemocytometer or an electronic cell counter. A direct optical measurement of cell density via an in situ microscope (ISM) eliminates the need for sampling and allows for continuous monitoring of this key parameter. Two such systems have been described in the literature, one of them has been developed at Mannheim University of Applied Sciences. This system has the advantage of not using any moving mechanical parts within or outside the fermentation vessel. Here we show two examples of advanced applications of a new version of this ISM with unprecedented resolution and frame rate: Adaptation to double glass jacket equipped bench top reactors and longer term application in a perfused 30 L steel reactor. Results in both cases show the performance of the ISM, the comparability of cell culture data obtained by ISM and traditional methods and the potential for further development of the ISM.

A Laboratory Experiment for Teaching Bioprocess Control -- Part 2: Bioprocess Design, Modelling, Simulation, and Fermentation Execution

Abstract This second paper on the development of a biotech teaching experiment focuses on the bioprocess itself: After identification of requirements of a bioprocess to be suited for a laboratory experiment for students, the mathematical models of the chosen process are presented in detail for batch, fed-batch, and continuous mode of operation. Linearization of the nonlinear dynamics reveals the system neither to be completely controllable nor to be completely observable – with biological reasons and solutions to this problem given. For fed-batch operation, the capabilities of the Simulink simulation environment to simulate different feeding strategies are shortly depicted. With specially tailored learning materials (“from students for students”), mastering the differences between “nice” simulation data and real-world sensor signals is addressed. Some comments on the development of an adapted strain of the microorganisms to the medium as the basis for a successful fermentation execution conclude this paper.

Optical Sampling in-situ Microscopy for on-line Monitoring of Animal Cell Cultures

Cell concentration and cell vitality are key parameters to be monitored during cell cultivation processes. Common techniques used for these purposes are often based on sterile sampling and subsequent off line measurements. Extraction and preparation of samples is labour-intensive and risk-entailing. These disadvantages are avoided if the cell culture is directly inspected by using an in-situ technique, e.g. an in-situ microscope (ISM). An ISM delivers a wealth of image data which can be evaluated so as to provide automatic monitoring of the cell density and of morphological parameters as the cell-size. In-situ microscopy can either employ periodic opening and closing of a probe chamber inside the reactor or, alternatively, flash illumination and optical depth of field in order to define a virtual probe zone. Here, we describe optics and software of an advanced version of such an ISM with unprecedented resolution and frame rate. Fast collection of online-galleries of individual cell-portraits even at low cell concentrations enables online morphological analysis without sample extraction. Cell density data obtained by the ISM and traditional counting are shown in comparison, revealing the advantage of the ISM with respect to statistic deviations.

On setting-up a portable low-cost real-time control system for research and teaching with application to bioprocess pH control

This paper describes the design and the setup of a portable low-cost real-time control system. All design decisions as well as the solutions to all practical problems, arisen during the implementation phase, are described in detail; therefore, this paper can serve as a guideline, helping the reader to have own systems up and running sooner.