SIMULTANEOUS FLOW-INJECTION ANALYSIS OF L-LACTATE AND L-MALATE IN WINE BASED ON THE USE OF ENZYME REACTORS

The simultaneous determination of L-malate and L-lactate, by enzyme-supported flow injection analysis (FIA), was developed using two enzyme reactors in parallel and a single oxygen electrode. NADH formed in the reaction of malate dehydrogenase (MDH) was regenerated to NAD+ with dissolved oxygen, using vitamin K3 and diaphorase (DI). L-Lactate was determined using the enzyme lactate oxidase (LOD). when sample solutions were simultaneously injected into the two reactors (the MDH-DI-reactor and the LOD-reactor) with a controlled residence time, a "train" of two peaks corresponding to L-lactate and L-malate were seen in the FIA-gram. The peak currents were linearly related to the L-malate and L-lactate concentration in the range 0.05-1.2 mM and 0.01-0.5 mM, respectively. The present system was applied to the determination of L-lactate and L-malate in wine. The results showed good agreement with those obtained using a conventional method (F-kit method), suggesting that this system may be applicable to the monitoring of malo-lactic fermentation during wine production.