New trends in measurement and control of biotechnological processes
To improve the biotechnological roduction processes, improved on-line anamainly on recent developments in on-line techniques, such as on-line aseptic sampling, on-line continuous flow analysis, on-line flow injection analysis, on-line HPLC, and online mass spectrometry. Methods for the determnation of the concentration and biological state of the cells are also taken into account as well as the necessity for sophisticated control. lysis techniques and better process contro P is necessary. The present review reports I NTRO D U CTI 0 N For the biosynthesis of cell mass, primary, and secondary metabolites as well as of enzymes for industrial and diagnostical applications and of proteins for therapeutical use, coordinated interplay of several enzymes is necessary. In order to achieve the full biological potential of the cells, the optimal environmental conditions of cell growth and product formation must be maintained in the bioreactor, at least with regard to the most important key parameters. The activity of a articular enzyme is controlled by the concentration of several cultivation medium compounds (e.g., ammonia), phosphates as well as induction of enzymes by their substrates. Generally speaking, high concentrations cause repression or inhibition, low concentrations reduce the growth and the product formation rate. At times, this optimal concentration range is very narrow. Several possibilities are available for controlling the concentration of key components: frequently, components of low solubility (e.g., peanut flour) are employed, or substrates are used (e.g., lactose) which can only be consumed slowly by the microorganisms. However, with strain improvement, the optimal concentrations of the key compoments may vary. Such flexible operation can only be realized by fast in situ or on-line process analysis suitable for process control. The control of the concentration of the limiting com onent is particularly difficult due to the low measurable components by means of a mathematical model. In the following, new in situ and on-line measuring techniques for fast analysis of medium components and characterisation of cell properties and their use for process control are presented. components. We P 1-known are enzyme regulations by carbon compounds (e.g., glucose), nitrogen concentration level. In that case, the concentration o P the key component often is calculated from ON-LINE MONITORING OF CULTIVATION M E D I U M COMPONENTS WITH LOW-MOLECULAR WEIGHTS In situ techniques are restricted to the measurement of dissolved oxygen (PO ), dissolved CO, (pCO,), hydrogen ion (pH), and redox otential (ref. 1). The concentration of t i e other medium septic, aseptic sampling from the reactor is necessary for on-line analysis. The most common on-line sampling systems use cross-flow filtration modules which are integrated into a medium recirculation loop (e.g., BIOPEM of B. Braun Diessel Biotech, Melsungen) (ref. 2 tubular in situ filters (e+, In situ Filter of ABC Bioverfahrenstechnik/ Biotechnologie, Puchheim (ref. 3). Contrary to the zn situ tubular filters, the cross-flow modules cannot be used for cultivations of shear-sensitive (e.g., animal) cells, microorganisms which quickly change their metabolism under oxygen-limited conditions (e.g., S. cerevkiue) and of recombinant microorganisms. components are measured ex sihc, outsi B e the reactor. Since most bioreactors are operated mono-