Real-Time Monitoring of Yeasts Growth Based on Bioimpedance Spectroscopy

Industrial bioprocesses usually occur in bioreactors, where the stages of a microorganism growth must be monitored to optimize the whole process. Off-line analytical methods are considered gold standard for such monitoring, but they are time consuming and may postpone important decisions making. Thus, there is always demand for the development of real time (on-line) monitoring methods for bioprocesses. Despite the existence of some real time methods used to measure the concentration of biomass in real time, such as optical density or turbidimetry, many of them are not able to distinguish living microorganisms from other materials, including dead microorganisms. This work proposes an on-line method for monitoring of total biomass, as well as the amount of viable cells, using a bioimpedance spectroscopy based on the current response to a step voltage excitation. To evaluate the proposed method, we performed an experiment of growth with yeast strain Saccharomyces cerevisiae species with initial inoculum of 0.1 and 0.5 g/L. The total amount of microorganism (using Neubauer chamber), the number of viable ones (using dyeing with methylene blue), and bioimpedance data were collected every hour during a period of 12 h. For each initial inoculum, series of data were collected. The results indicate the proposed technique presents good prediction of the total amount of microorganism (\( r = 0.918 \)) and of the number of viable ones (\( r = 0.858 \)).