In fermentations, where it is necessary to provide increasing high density biomass (for example, it is typical for recombinant protein biosynthesis, using E.coli strains), the choice of optimal substrate feeding profile is substantial. Scientific publications describe specifically created experimental systems for implementation of fermentations with automatically controlled feeding, based on mathematical models. Despite this, commercially available bioreactor controllers only provide possibilities for operators to set feeding profiles by time and to control substrate feeding speed depending on the рО2 sensor readings.
A particularity of the fermentation processes is the impossibility of providing fully repeatable fermentations, even under absolutely identical cultivation conditions. This is both due to the properties of the strain of cultivated microorganism used and due to other not always known factors. As a result, for ensuring optimal feeding profile it must be constantly corrected depending on the particular fermentation process implementation. It means that the evaluation and input of updated feeding profiles directly depend on the skill of the operator. Considering that this operation requires a very high level of training and skill of the operator, the risk of error is relatively large, which is contrary to the requirements of GMP. It means that solutions must be sought in order to reduce dependence on the operator, when performing the above technological operation.
In order to solve this problem, we have created a fermentation control system according to the following flowchart.
This flowchart assumes that the user already has a complete bioreactor in order to implement fermentations. The platform scales are connected to the controller (based on Siemens Simatic) via serial port RS485 using exchange protocol Modbus RTU. The software SCADA for substrate feeding control must run simultaneously (up to several minutes) when starting the fermentation process.
In our control system, the software SCADA is connected to the feeding simulation software developed on the MATLAB base. Before starting the fermentation process, the initial data must be put into the software SCADA — the volume of the culture medium, the biomass and glucose (or other source of sugars) concentration, and also the initial feeding profile must be set (calculated using the MATLAB).
During the fermentation process, samples are taken in order to input the current results of the tests on biomass and glucose (or other sugars) in the software SCADA. Performed the input of the results of the tests, the software MATLAB performs automatic comparison of these results with the results of calculations according to the adopted mathematical model. If the deviations are above the set standards, the software MATLAB performs calculation of the new feeding profile. The updated feeding profile is automatically uploaded into the controller, and the substrate feeding is further implemented according to the new profile (up to a following update).
E.coli fermentations were carried out using this control system. Automatic substrate feeding cultivation processes were compared to the processes whose optimal feeding profiles were set by the operator, before starting the cultivation.
The above fermentation process control system can be successfully used at the stage of technology development, as well as in the industrial fermentations that meet the modern requirements of GMP.