A green bean homogenate immobilized on chemically crosslinked chitin for determination of caffeic acid in white wine

A new green bean (Phaseolus vulgaris) tissue homogenate-based biosensor was developed for the square-wave voltammetric determination of caffeic acid in white wine. The biosensor was constructed by immobilization of green bean tissue homogenate, as a source of peroxidase, in a chemically crosslinked chitin matrix with epichlorohydrin and glutaraldehyde that was incorporated in a carbon paste electrode. In the presence of hydrogen peroxide the peroxidase catalyses the oxidation of caffeic acid to quinone and the electrochemical reduction of the product was obtained at a fixed potential of +0.10 V versus Ag/AgCl (3.0 mol L-1 KCl). The response characteristics and optimization of the bioelectrode design were evaluated. The recovery of caffeic acid from three samples ranged from 91.0 to 103.1 % and a rectilinear calibration curve for caffeic acid concentrations from 2.0 x 10(-5) to 2.0 x 10(-4) mol L-1 (r = 0.9990) was obtained. The detection limit was 2.0 x 10(-6) mol L-1 and the relative standard deviation was 2.2% for a solution containing 1.2 x 10(-4) mol L- 1 caffeic acid and 2.0 x 10(-3) mol L-1 hydrogen peroxide in 0.1 mol L-1 phosphate buffer solution at pH 7.0 (n = 10). The long-term stability of the biosensor was 300 days. (c) 2006 Elsevier Inc. All rights reserved.