Selective determination of lactic acid in dry-fermented sausages using a sensor based on immobilized lactate oxidase

Selective determination of lactic acid in dry-fermented sausages is an indicator of quality and its presence prevents the growth of pathogenic bacteria. The analysis of lactic acid represents a high cost for the relevant food industries. The use of an enzymatic sensor would allow to reduce the time and cost of this analysis. An enzymatic sensor employing lactate oxidase (LacOx) with the immobilized enzyme system in combination with an oxygen electrode was optimized to determine the lactic acid content in dry-fermented sausages. In this study using LacOx from Pediococcus sp., a voltage of -600 mV, low volumes of reaction and the amperometric signal obtained due to the oxygen depletion (consumed oxygen) during the lactic acid oxidation was recorded at 15 s in the immobilized enzyme sensor so that the reaction rates (slope) were related to the lactic acid content. A positive linear relationship between the consumed oxygen as a function of time (mg O2/L*s(-1)) and the lactic acid concentration in the range of 250-600 mu M, with a coefficient ofR(2) = 0.9936 for the immobilized enzyme system, was determined. The immobilized enzyme sensor showed a high specificity K-M = 0.865 and sensitivity of 0.25 mM and was stable enough to allow the reutilization of the membranes up to 20 times without loss of activity, where 90% of its initial activity remained after 45 days. The analysis of lactic acid with the immobilized enzyme system in dry-fermented sausages revealed very good agreement with the determination performed through standard HPLC methodology using the same linear range in both methods, which validated the use of this sensor as an alternative technique to evaluate cured meat quality.