An on-line system for glucose monitoring during fermentation was developed. The system employed flow-injection analysis coupled with a wall-jet electrode. Glucose was converted enzymatically in a tubular reactor packed with controlled pore glass beads containing immobilized glucose oxidase. The hydrogen peroxide produced was detected amperometrically. A filtration/sampling module operated by a peristaltic pump enabled sample withdrawal from the fermenter. The system was interfaced to a programmable language controller which was in turn linked to a microcomputer. The dual injection valve of the flow system was operated in a novel configuration to achieve sample dilution, by dispersion, and standardization simultaneously.
The developed system was characterized for dilution factor, stability and linearity of response. After conditioning of the reactor, sample peak heights were found to have a precision of 1.07% (R.S.D., 25 determinations) when the glucose concentration was 1.32 g 1-l. Under the conditions studied, linear response to glucose concentration from 0.062 to 4.0 g 1-l was obtained. Sample throughput was about 7 per hour. Interferences from the fermentation media were negligible after filtration through the sampling module and dilution. The on-line system was applied to glucose monitoring during E. coli fermentation.
Good results were obtained as shown by the high cell density COD,,, = 168 in 9 h fermentation), constant specific growth rate ( p = 0.66) and lower acetate accumulation (less than 2 g 1-l when OD,,, was over 50).