Question

Physical and chemical parameters of fermentation process

Answer 1

Chemical Parameters

pH

Substrate concentration

Product concentration

O2 concentration (dissolved)

Waste gases concentration (e.g. CO2)

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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 CO2concentrations 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.


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.