Amperometric determination of total assimilable sugars in fermentation broths with use of immobilized whole cells

A microbial sensor consisting of immobilized living whole cells of Brevibacterium lactofermentum and an oxygen electrode was prepared for continuous determination of total assimilable sugars (glucose, fructose and sucrose) in a fermentation broth for glutamic acid production. Total assimilable sugars were evaluated from oxygen consumption by the immobilized microorganisms. When a sample solution containing glucose was applied to the sensor system, increased consumption of oxygen by the microorganisms caused a decrease in the dissolved oxygen around the Teflon membrane of the oxygen electrode and the current of the electrode decreased markedly with time until steady state was reached. The response time was ≈ 10 min by the steady state method and 1 min by the pulse method. A linear relationship was found between the decrease in current and the concentration of glucose (<1 mM), fructose (<1 mM) and sucrose (<0.8 mM). The ratio of the sensitivity of the microbial sensor to glucose, fructose and sucrose was 1.00:0.80:0.92. The decrease in current was reproducible to within 2% of the relative standard deviation when a sample solution containing glucose (0.8 mM) was employed for experiments. The selectivity of the microbial sensor for assimilable sugars was satisfactory for use in the fermentation process. The additivity of the response of the microbial sensor for glucose, fructose and sucrose was examined. The difference between the observed and calculated values was within 8%. The microbial sensor was applied to a fermentation broth for glutamic acid production. Total assimilable sugars can be determined by the microbial sensor which can be used for more than 10 days and 960 assays.