ENZYME ASSAYS FOR THE PHENOLIC CONTENT OF NATURAL JUICES

The properties of a fungal laccase have been exploited to develop two enzyme assays for the phenolic content of natural beverages: first, by monitoring the fall in oxygen tension after addition of enzyme to a diluted juice sample in an end-point batch assay; second, by monitoring the current due to reduction of products after injection of sample into a flow injection analysis (FIA) system which incorporates the immobilized enzyme. Using apple juices, a linear (R > 0.9) correlation was observable between these enzyme assays and the Folin-Ciocalteu wet chemical assay for total phenol content. Using purified substrates, a study has been made of those phenolic constituents measured in the two enzyme assays. Oxidative treatment of juices with laccase was shown by HPLC to specifically remove these phenolics. These enzyme assays may prove helpful to predict the stability of natural beverages.