Screening of Polyphenols in Grape Marc by On-Line Supercritical Fluid Extraction – Amperometric Detection with a PVC-Graphite Composite Electrode

Abstract

An on-line supercritical fluid extraction (SFE)-amperometric detection system was developed and applied to the screening of polyphenols in grape marc samples. A liquid trap was used as an interface between the supercritical fluid extractor and the amperometric detector. Epicatechin was selected as reference polyphenol compound for optimizing the extraction conditions as well as the amperometric detection, for which a previous voltammetric study was carried out. For the extraction process a temperature of 50 °C and a CO2 fluid density of 0.9 mg/mL, modified with 10% of purified water, were used. A saline buffer compatible for the amperometric detection was employed as solvent trapping. The proposed method was used to determine the total content of polyphenols in different types of grape marc. Linear calibration plots were obtained in the range 2.9–29 μg mL−1. The limit of detection was 3.57 μg mL−1 for epicatechin.