C. I. S. Fernandes, M. J. F. Rebelo^*

CCMM -Faculdade de Ciências da Universidade de Lisboa, Campo Grande, C 8, 1749-016 Lisboa, Portugal

Received 6 January 2009; accepted 5 May 2009

Abstract

New developments in the utilization of a laccase based polyphenolic biosensor were done in order to optimize its application in wines. Laccase was immobilized on polyether sulphone membranes and applied on an Universal Sensors (US) electrode base system containing a platinum working electrode and silver, silver chloride electrode.

Caffeic acid was dissolved either in tartarate standard buffer solution at pH 3.5 or in 12% ethanol tartarate standard buffer solution at pH 3.5. The referred values of pH and ethanol percentage are the average values of table wines.

Wines from different regions of Portugal, namely Grão Vasco (Dão), A P_Cabernet (Setúbal), C P_Castelo de Syrah (Setúbal), Ol (Alentejo), A P (Alentejo) and Quinta dos Poços (Douro), were studied. Grão Vasco was taken as a reference. It was observed that Grão Vasco (Dão) wine presented a caffeic acid equivalent concentration superior to the other studied wines, followed by a Douro wine: Quinta dos Poços (values of 17.00 and 12.18 mg/L, respectively, were found). It was also possible to verify that the two latter referred wines did not inhibit the biosensor, which could be reused after having been dipped in those wines. However, the wines from Setúbal and Alentejo, studied in this work, have a caffeic acid equivalent concentration lower than the other two mentioned before and seemed to inhibit the system, since the biosensor response decreased after being used in them. It was, thus, not possible to do several assays with the same membrane, when those wines were used. Reproducibilities were better for caffeic acid standard solutions, Grão Vasco and Quinta dos Poços wines, than for the other wines. In fact RSDs (Relative standard deviations) of the order of 1.1, 1.4 and 5.0% were obtained for caffeic acid standard solution, Grão Vasco and Quinta dos Poços wines,whereas 20% was found in the Setúbal and Alentejo studied wines. Two particular wines, A P_Cabernet and A P, were studied in more detail. Cyclic voltammograms and biosensor responses of these two wines indicate that A P has more caffeic acid equivalents than the A P_Cabernet.

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^*Corresponding author.: E-mail address: mjrebelo@fc.ul.pt