An automated flow injection analysis system for on-line monitoring of glucose and L-lactate during lactic acid fermentation in a recycle bioreactor

The study concerns on-line sequential analysis of glucose and L-lactate dur ing lactic acid fermentation using a flow injection analysis (FIA) system. Enzyme electrodes containing immobilized glucose oxidase and L-lactate oxid ase were used with an amperometric detection system. A 12-bit data acquisit ion card with 16 analog input channels and 8 digital output channels was us ed. The software for data acquisition was developed using Visual C++, and w as devised for sampling every hour for sequential analyses of lactate and g lucose. The detection range was found to be 2-100 g l(-1) for glucose and 1 -60 g l(-1) for L-lactate using the biosensors. This FIA system was used fo r monitoring glucose utilization and L-lactate production by immobilized ce lls of Lactobacillus casei subsp. rhamnosus during a lactic acid fermentati on process in a recycle batch reactor. After 13 h of fermentation, complete sugar utilization and maximal L-lactate production was observed. A good ag reement was observed between analysis data obtained using the biosensors an d data from standard analyses of reducing sugar and L-lactate. The biosenso rs exhibited excellent stability during continuous operation for at least 4 5 days.