MICROBIAL SENSOR FOR ONLINE DETERMINATION OF MICROBIAL-POPULATION IN A FERMENTER

The beer yeast cell population in a fermenter has been determined continuously by using an electrode flow system. This system comprises a flow cell and electrodes consisting of a platinum anode and a glassy carbon cathode inserted in a solution of K3Fe(CN)6 and K4Fe(CN)6. The principle of cell-number determination is based on sensing a redox dye reduced by the microorpnism. The electrode is immersed in a phosphate buffer solution (0.1 mol/l, pH 6.2) containing a redox dye (2,6-dichlorophenol-indophenol) and the generated current is measured. The response time of the electrode system is 5 min and the generated current is proportional to the cell population from 10(6) to 10(7) cells/ml. The currents are reproducible. The method is simple and rapid, and the sample does not need any pretreatment. Furthermore, the beer yeast cell population measured with the electrode flow system is in good agreement with results obtained by means of visual counts with a haemocytometer and a microscope.