Measurement Techniques in Bioprocess Monitoring

d. Carbohydrate Measurement. The operational mechanism of a direct reading glucose sensor described by Solomons (1969b) was based on the activity of the enzyme glucose oxidase (Updike and Hicks, 1967). Hydrogen peroxide is produced during the reaction and is detected using electrochemical amperometric detectors. This technique has been used to develop a number of reactions for both offline and online measurement. With the allegedly growing methods for biochemical conversion of carbohydrates (such as cellulose-glucose and starch-glucose conversions) for a variety of applications, the significance of these sensors should be underlined. An online functioning glucose analyzer with a sterilizable probe was introduced by Leeds & Northrup, which is seen to be a significant development and will be covered later. On the basis of present patterns, it is envisaged that dialysis membrane-based continuous culture One approach to resolving the challenge of sample removal and treatment prior to wet chemical tests in fermentation technology is broth sampling (cf Section III, D, 2, c). e. Cell Mass Measurement. The automatic measurement of fermentation broth cell mass remains one of the most challenging issues. The most typical method is to gauge how much light can pass through the soup. The approach is based on the idea that the turbidity, which is connected to the number of cells present, is proportionate to the intensity of the transmitted light. The following list of restrictions applies to all devices created in the last ten years, including Turbidostat from New Brunswick

Scientific Co. and Nephelostat by Peraino and Eisler. (1) Only discrete "spherical" things may be detected; filamentous fungi cannot be quantified with current technology. Devices are useful for specific bacterial, yeast, or mammalian cell cultures. (2) Only clear solutions can be used with the procedure. molasses, calcium carbonate, starch, and maize steep liquor are examples of insoluble and opaque elements that may be present in industrial culture media but are not appropriate to soluble culture media. (3) Above a cell concentration of 5 gm/liter, the relationship between cell concentration and light transmittance typically deviates from linearity. The use of such machinery for broad scientific research is constrained by these issues. Separate evaluations must be performed to establish the relationship between the transmitted light intensity and the actual cell population or mass present in those circumstances when application is feasible. The literature typically presents data in dry weight (DW) or cell numbers (for example, 103 cells/ml). Engineering-wise, the latter dimension is favoured because it allows for a material balance. Then the yield of conversion can be determined. Dry cell mass has not yet been directly determined automatically and successfully for broad use in the literature. 2. Off-Line Automatic Analyzers Due to challenges in the development of steam sterilizable on-line reading sensors for the detection of different metabolites, off-line analytical systems that repeatedly and/or continuously sample exhaust gases to monitor particular parameters are now used. Sampling devices typically consist of a sterile conduit that connects the specific analyser to the gases emitted by the culture. The methodologies that have withstood the test of initial field experience and are

likely to be utilised in the future for quasi-online chemical analysis of chemicals of interest in biological processes are discussed in the following paragraphs. a. Gas Chromatography. According to multiple studies (Hamer, 1967; George and Gaudy, 1973; Abbott et al., 1973), off-line measurement of several volatile chemicals (such as methane, acetaldehyde, and ethanol) using gas chromatographs has been successfully tested in biochemical processes. O'Brien and Cecchini (1970) described one of the most elegant applications when they examined the metabolic processes of bacteria by identifying their end products (alcohols, di-, and tricarboxylic acids), and then used this "finger print" for taxonomy identification. Although this application has not yet been documented in the literature, it is interesting to highlight that this approach may also have practical implications for the identification of specific types of contamination in pure culture. Gas Chromatograph (GC) technology has recently advanced to the point that it is now possible to link them to the exit gas lines of fermentors. Hewlett-Series Packard's 5830A, Reporting Gas Chromatograph, is one example. With an automatic sampler, this instrument can be connected to up to 16 sample lines. It features a dual thermal conductivity detector, an oven temperature controller, and automatic data integration and reporting in alphanumeric and/or graphical representations. For computer interaction, signals can also be retrieved in binary coded decimal (BCD) form. The effects of C/N feed ratios on protein and ethanol production for yeast growing on molasses have been verified using an HP5830A GC. Figure 6 displays the GC profile of a C. utilis culture taken at 15-minute

intervals for N2, C02, H20, acetaldehyde, and other gases (G. M. Toth and L. K. Nyiri, unpublished observation). ethanol. For molecular weights up to ethanol, take note that the overall sample retention time was little under 3 minutes. Gas chromatography has the benefit of allowing for the automatic determination of a sizable variety of chemicals. Since the reporting frequency is determined by the retention time and the number of compounds being analysed, its drawbacks include (1) the discontinuous signal produced and the time between signals; (2) the relatively high cost, which can be partially offset if several fermentors are to be monitored; and (3) the practical issue, which requires investigation for each scale of use: to what extent do the volatile compound concentrations in the exit gas ref When ethanol and acetaldehyde are used as an example, the At a specific gas flow rate, one might calculate the liquid-gas distribution ratio.