Amperometric carbon paste biosensor based on plant tissue for the determination of total flavanol content in beers

Apple tissue containing polyphenol oxidase was incorporated in carbon paste matrix to make a biosensor for the analysis of flavanols in beers. The electrochemical and structural properties of different carbon paste compositions were assessed using ac impedance, other electrochemical techniques and scanning electron microscopy. Results are discussed regarding electroactive surface, mechanical stability, impedance parameters and surface roughness of the carbon pastes. From these results, an optimum graphite/Nujol ratio of 4 was chosen and applied to the construction of apple-based biosensors. The electrochemical, morphological and analytical properties of these sensors were investigated with respect to biomolecule loading. The analytical properties (sensitivity, Imax) of these biosensors increased with plant tissue loading. This result was correlated with ac impedance parameters, electroactive surface and carbon paste morphology. A biosensor using a plant tissue/carbon paste ratio of 0.086 was used to assess sensitivity and selectivity to various flavanols and phenolic compounds.