A multi-enzyme bioelectrode for the rapid determination of total lactate concentration in tomatoes, tomato juice and tomato paste

This work presents a new multi-enzyme bioelectrode for the combined determination of d(−)-l(+)-lactic acid in samples of whole tomatoes, chopped tomatoes, tomato paste and tomato juice. The principle of the biosensor is based on the catalytic activity of the enzymes l(+)-lactic acid oxidase (LOD), d(−)-lactic acid dehydrogenase (D-LDH) and horseradish peroxidase (HPO). The three enzymes are immobilized on the tip of an amperometric oxygen selective electrode. The total concentration of d(−)-l(+)-lactic acid is proportional to the amount of O2 consumed. The biosensor has been tested for standard solutions of d(−)-l(+)-lactic acid, as well as for real samples. The latter set of experiments has been carried out in three different laboratories, indicating a good repeatability and reproducibility of the obtained results. The main characteristics of the lactate biosensor on real samples (whole tomatoes, chopped tomatoes, tomato paste and tomato juice) have been compared, in terms of both analytical and practical features, with those of a traditionally employed enzymatic-spectrometric technique, based on the oxidation of d-l-lactic acid, catalysed by d-lactate dehydrogenase and l-lactate dehydrogenase, with production of pyruvate and NADH, and on the subsequent spectrometric determination, at λ= 340 nm, of the NADH formed.