SIMULTANEOUS MONITORING OF GLUCOSE AND L-LACTIC ACID DURING A FERMENTATION PROCESS IN AN AQUEOUS 2-PHASE SYSTEM BY ONLINE FIA WITH MICRODIALYSIS SAMPLING AND DUAL BIOSENSOR DETECTION

The production of L-lactic acid by Lactococcus lactis (ATCC 19435) dur ing fermentation in an aqueous two-phase system (ATPS) was monitored o n-line using microdialysis sampling coupled to a dual flow-through ele ctrochemical cell housing glucose and lactate biosensors, which enable d the simultaneous and selective monitoring of both glucose and L-lact ic acid. The amperometric biosensors were based on the co-immobilisati on of glucose oxidase (GOD) for the glucose sensor and L-lactate oxida se (LOD) for the lactate sensor, respectively, with horseradish peroxi dase (HRP) in a carbon paste matrix. The sensors characterised regardi ng 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 monitori ng of both glucose and L-lactic acid simultaneously, allowing a sampli ng frequency of 15 h(-1) and with a delay between sampling and detecti on of less than 3 min. Comparison of the on-line measurements with a s tandard off-line analysis using HPLC agreed well suggesting the suitab ility of the system for application in very complex matrices. (C) 1998 Elsevier Science B.V.