Estimation of Fermentation Biomass Concentration by Measuring Culture Fluorescence

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Abstract
The fluorescence of a fermentation culture was studied for its application as an estimator of biomass concentration. The measurement was obtained by irradiating the culture with UV light (366 nm) through a glass window and detecting fluorescent light at the window surface at 460 nm. Over 1/2 of the fluorescent material was intercellular NADH, with the remainder being NADPH and other unidentified intercellular and extracellular fluorophores. The culture fluorescence was a function of biomass concentration, together with environmental factors, which presumably act at the cellular metabolic level to modify intercellular NADH pools (e.g., dissolved O2 tension, energy substrate concentration and inhibitors). When these environmental conditions were controlled, a linear relationship was obtained between the log of the biomass concentration and the log of the fluorscence. Under these conditions, this relationship has considerable potential as a method to provide real-time biomass concentration estimates for process control and optimization since the fluorescence data is obtained on line. When environmental conditions are variable, the fluorescence data may be a sensitive index of overall culture activity because of its dependence on intercellular NADH reserves and metabolic rates. This index may provide information about the period of maximum specific productivity for a specific microbial product. [Saccharomyces cerevisiae, Streptomyces and Thermoactinomyces were used in these studies.].