Fermentation of Saccharomyces cerevisiae (bakers’ yeast)In biotechnology, especially during fermentation, the methods of measuring physical and chemical parameters such as temperature, pH-value, dissolved oxygen (DO), CO2 have been welll established. On the other hand process-suitable methods for the monitoring of biological parameters such as cell concentration or metabolic changes are still not wide spread.
Using a fiber optical instrumental setup consisting of a combined fluorescence / light scattering probe, a CCD spectrometer and a Xenon lamp it was possible to monitor both the culture fluorescence and the cell concentration for a 29-hour batch fermentation of S. cerevisiae. The optical probe is equipped with two spectral filters. The short pass filter (F1) in the excitation pathway has significant transmission only in the spectral regions between 300 to 400 nm (fluorescence excitation) and 700 to 850 nm (light scattering signal), but it blocks the output of the Xenon lamp in the region between 400 to 700 nm to avoid an interference with the fluorescence emission of the biofluorophores. The transmitted light irradiates the yeast suspension in front of the probe, where it excites intracellular fluorophores such as reduced nicotinamide adenine dinucleotide (NAD(P)H), pyridoxine derivatives, flavins (FAD, FMN) and porphyrins. The fluorescence emission is shifted towards longer wavelengths in comparison to the excitation spectrum. A small fraction of the fluorescence light reaches the detection fiber of the probe, where the long pass filter blocks all light below 435 nm.
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