Biosensors for L-malate and L-lactate based on solid binding matrix Original Research Article

Biosensors for the selective determination of L-lactate and L-malate in wine based on robust solid composite transducers are presented. Transducers comprised a solid binding matrix having hydrophobic skeleton, e.g. 2-hexadecanone, graphite and NAD+. The enzymes, L-malate or L-lactate dehydrogenase and diaphorase, were placed onto the transducer surface and covered by a dialysis membrane, which substantially reduced interferences derived from easily oxidable compounds, e.g. polyphenols, of wine. Hexacyanoferrate(III) was used as a mediator. The electrode responses were linear up to 1.1 mM for L-malate and 1.3 mM for L-lactate. The detection limit was at about 10 μM. The biosensors showed an excellent long-term stability, after five months storage at room temperature, the L-malate sensor exhibited almost 100% and L-lactate 90% of the initial sensitivity. A multisensor composed of two enzyme electrodes allowing a simultaneous determination of L-malate and L-lactate was also constructed. The results obtained from the determination of both acids in wine samples by biosensors were in a good agreement with those obtained by liquid chromatography.