Graphite-Teflon composite bienzyme electrodes for the determination of L-lactate: Application to food samples

A bienzyme amperometric graphite-Teflon composite biosensor, in which lacta te oxidase (LOD) and peroxidase, together with the mediator ferrocene, are incorporated into the electrode matrix, was developed for the determination of L-Iactate in food samples such as wine and yogurt by using both batch- and flow-injection modes. This bienzyme electrode was fabricated by simple physical inclusion of the enzymes and the mediator in the bulk of the graph ite-Teflon matrix. A Teflon content of 70%, an applied potential of 0.00 V, and a pH of 7.4 were employed as working conditions. The composite bioelec trode exhibited long-term operation because of the renewability of its surf ace by polishing. Reproducible amperometric responses were achieved with di fferent electrodes fabricated from different composite matrices, and no sig nificant loss of the enzyme activity occurred after 6 months of storage at 4 degrees C. Detection limits for L-lactate of 1.4 and 0.9 mu M were obtain ed by batch amperometry in stirred solutions and flow-injection with ampero metric detection, respectively. An interferences study with different subst ances which may be present in wine and yogurt together with L-lactic acid d emonstrated very good selectivity for the determination of this analyte. Th e bienzyme composite electrode was applied to the determination of L-lactic acid in red wine and shaken yogurt, and the methods were validated by comp aring these results with those obtained by applying a recommended reference method. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.