Determination of flavanols in beers with tissue biosensors

Various plant tissues containing polyphenol oxidase were incorporated in carbon paste electrodes to make biosensors for the determination of catechol related components in beers, principally flavanols such as catechins and their dimers and trimers. Calibration graphs were produced for each plant tissue with both catechol and (-) epicatechin as standards. The response of the banana based sensor was rather erratic and showed a large zero error, probably due to flavanols in the banana. Potato, wet apple and dried apple were all satisfactory. The response with dried apple was 60% that of wet apple, but showed greater stability. The response of (-)epicatechin was 1.4 to 1.5 times that of catechol with wet or dried apple. Banana and potato based sensors were used for the determination of total flavanols in a range of commercial beers and lagers. Results with the banana were rather high due to the zero error. Good analytical data were obtained with potato, comparable to those obtained using colorimetric or liquid chromatographic analyses.