Parameters of Bioprocess and its Measurement

Read this article to learn about the various physical, chemical and biological parameters of bioprocess that can be measured during fermentation/bioprocessing.

There are a large number of physical, chemical and biological parameters that can be measured during fermentation/bioprocessing (Table 19.6) for data analysis and appropriate control. Some special sensors have been developed to carry out measurements in the bioreactors. The basic requirement of all the sensors is that they must be sterilizable. The measurements of the parameters (listed in Table) can be done either directly in the bioreactor or in the laboratory.

Important Parameters that can be measured during bioprocessing are :

Physical Parameters

Temperature

Pressure

Flow rates

Viscosity

Turbidity

Power consumption

Chemical Parameters

pH

Substrate concentration

Product concentration

O₂ concentration (dissolved)

Waste gases concentration (e.g. CO₂)

Ionic strength

Biological Parameters

Activities of specific enzymes

Protein concentration

Energetics (ATP concentration)

DNA/RNA content

pH measurement:

There are pH electrodes that can withstand high temperature (sterilization) pressure and mechanical stresses, and yet measure the pH accurately. Combination electrodes (reference electrode, glass electrode) are being used. In fact, electrodes are also available for measuring several other inorganic ions.

O₂ and CO₂ measurement:

Oxygen electrodes and CO₂ electrodes can be used to measure O₂ and CO₂ concentrations respectively. The electrodes are amperometric in nature. They are however, susceptible for damage on sterilization. In a commonly used technique, O₂ and CO₂ respectively can be measured by the magnetic property of O₂ and the infrared absorption of CO₂. This can be done by using sensors.

Use of Mass Spectrometer:

The mass spectrometer is a versatile technique. It can be used to measure the concentrations of N₂, NH₃, ethanol and methanol simultaneously. In addition, mass spectrometer is also useful to obtain information on qualitative and quantitative exchange of O₂ and CO₂.

Use of Gas-permeable Membranes:

The measurement of dissolved gases, up to 8 simultaneously, can be done almost accurately by using gas-permeable membranes. The advantage is that such measurement is possible to carry out in the nutrient medium.

Use of Computers:

Computers are used in industrial biotechnology for data acquisition, data analysis and developing fermentation models.

Data acquisition:

By employing on-line sensors and computers in fermentation system, data can be obtained with regard to the concentration of O₂ and CO₂, pH, temperature, pressure, viscosity, turbidity, aeration rate etc. Certain other parameters (e.g. nutrient concentration, product formation, biomass concentration) can be measured in the laboratory i.e. off-line measurements. The information collected from on-line and off-line measurements can be entered into a computer. In this fashion, the entire data regarding a fermentation can be processed, stored and retrieved.

Data analysis:

The data collected on a computer can be used for various calculations e.g. rate of substrate utilization, rate of product formation, rates of O₂ uptake and CO₂ formation, heat balance, respiratory quotient. Through computer data analysis, it is possible to arrive at the optimal productivity for a given fermentation system.

Development of fermentation models:

The computer can be used to develop mathematical models of fermentation processes. These models in turn will be useful to have a better control over fermentation systems with high productivity in a cost-effective manner.