Composite amperometric tyrosinase biosensors for the determination of the additive propyl gallate in a reversed micellar medium

The use of a composite graphite-Teflon-tyrosinase biosensor for the determination of the additive propyl gallate in fatty food samples is reported. The compatibility of this composite biosensor with predominantly nonaqueous media allowed the use of reversed micelles-formed with ethyl acetate as the continuous phase, a 5% of a phosphate buffer solution of pH 7.4 as the dispersed phase, and 0.10 mol L−1 dioctyl sulfosuccinate (AOT) as the emulsifying agent-as a suitable working media for the determination of propyl gallate. Monitoring of the enzyme reaction involving the additive was performed by electrochemical reduction (at −0.10 V) of the corresponding o-quinone formed during the catalytic oxidation of propyl gallate. Composite bioelectrodes allow the regeneration of the electrode surface by polishing and exhibit long-term operation (70 days). Moreover, the behaviour of PG as an inhibitor-like of the phenol oxidation reaction catalysed by tyrosinase was studied from an analytical point of view. This process is due to a competition of the two substrates for the enzyme active centers. The analytical characteristics were very similar using both measurement methodologies (the direct amperometric and the inhibition-like responses). Performance of the composite biosensor for the analysis of propyl gallate in foodstuffs was checked using lard as a sample. An aliquot of the analyte extract in ethyl acetate was transferred directly to the electrochemical cell containing the reversed micellar medium.