A fully automated method for in real time determination of laccase activity in wines

An automated method for determining laccase activity in musts and wines is here presented. The method is based on the Flow Injection technique using the mode of stop-flow at the detector with monitoring of the absorbance change caused by the oxidation of the substrate (syringaldazine). All the units that form the autoanalyser are controlled by a computer program for automating continuous processes developed by the authors. This work was aimed at providing wineries with a new tool for evaluating the degree of infection by Botrytis cinerea that overcomes the disadvantages involved in the determination of gluconic acid. In addition, a study of the relationship between the content of gluconic acid and laccase activity was carried out and no relationship was found. Thus, this acid is not an appropriate marker for evaluating infection by Botrytis. The analytical method was characterised and the limit of detection and limit of quantification were 0.2 and 0.6 U ml−1, respectively. The linear range was 0.6-24.0 U ml−1. This range is enough for the application of the method to wine; nevertheless, an enlargement of the range, if required, could be obtained with a higher dilution factor. Repeatability and reproducibility, expressed as relative standard deviation, were 4.0 and 6.5%, respectively. The total time necessary per analysis is 12 min. The method can be used as a routine method at grape reception in wineries.