FLOW-INJECTION ANALYSIS OF MICROMOLAR CONCENTRATIONS OF GLUCOSE AND LACTATE IN FERMENTATION MEDIA

Flow-injection analysers for glucose and lactate were optimized for the measurement of very low concentrations in complex fermentation media. The analytes were enzymatically oxidized and the hydrogen peroxide formed was detected by chemiluminescence. The enzymes were immobilised on a nylon tube and by measuring the flow-rate dependence of the conversion of hydrogen peroxide by catalase the performance of differently knitted enzyme reactors was evaluated. In the resulting glucose and lactate analysers the limits of determination in aqueous solutions were 50-mu-g l-1 lactic acid and 150-mu-g l-1 glucose. When measuring glucose concentrations in the range 0.5-10 mg l-1 the purity of the enzyme used in the analyser must be high. The analysers were used to study bacterial and yeast fermentations, in particular the product formation pattern at very low glucose concentrations and the microbial preference for alpha- and beta-glucose.