Simultaneous monitoring of glucose and L-lactic acid during a fermentation process in an aqueous two-phase system by on-line FIA with microdialysis sampling and dual biosensor detection

The production of L-lactic acid by Lactococcus lactis (ATCC 19435) during fermentation in an aqueous two-phase system (ATPS) was monitored on-line using microdialysis sampling coupled to a dual flow-through electrochemical cell housing glucose and lactate biosensors, which enabled the simultaneous and selective monitoring of both glucose and L-lactic acid. The amperometric biosensors were based on the co-immobilisation of glucose oxidase (GOD) for the glucose sensor and L-lactate oxidase (LOD) for the lactate sensor, respectively, with horseradish peroxidase (HRP) in a carbon paste matrix. The sensors characterised regarding the sensitivities, pH optima and operational stabilities were found to be satisfactory within the required range and time of measurements. The on-line setup was found to be a flexible system for the monitoring of both glucose and L-lactic acid simultaneously, allowing a sampling frequency of 15 h(-1) and with a delay between sampling and detection of less than 3 min. Comparison of the on-line measurements with a standard off-line analysis using HPLC agreed well suggesting the suitability of the system for application in very complex matrices. (C) 1998 Elsevier Science B.V.