A Highly Sensitive Caffeic Acid Fluorescent Probe for Detecting Laccase in Grape Juice and Mushrooms

Abstract

Laccase is a kind of copper-containing polyphenol oxidase with similar properties of different sources, of which catalytic reaction requires only oxygen and releases only water. The most widely used method for laccase detection is spectrophotometric assay with limited sensitivity. Herein, we report a highly sensitive fluorescent method for detecting the activity of laccase. This probe shows high selectivity, reliable accuracy as well as a good linear relationship toward different concentrations of laccase. Upon reaction, a new absorption peak appears around 420 nm accompanied by a significant fluorescence increase at 470 nm, which was consistent with the conjugation extension after the polyphenol structure was oxidized to quinone. The effects of different inhibitors and metal ions on the activity of laccase were assessed and this probe was compared with a commercial laccase detection kit showing higher sensitivity. Further, this method was successfully used for the determination of laccase in grape musts with different degrees of fermentation as well as in three kinds of mushroom extracts.