SCREENING OF POLYPHENOLS IN GRAPE MARC BY ON-LINE SUPERCRITICAL FLUID EXTRACTION-FLOW THROUGH SENSOR

An on-line supercritical fluid extraction continuous flow manifold including a flow through sensor was used and applied to the quantitative determination of total polyphenols in grape marc samples. A clean, highly selective supercritical fluid extraction (SFE) method for the isolation of phenols from grape marc samples was optimised. Dried, ground, and sieved grape marc (0.1 g) were subjected to SFE with CO2 modified with 5% methanol at 350 bar and 50°C(CO2 density 0.9 g ml(-1) for 15 min at a liquid flow-rate of 4 ml min-1. Diatomaceous earth was used to reduce the void volume of the extraction vessel. The analytes were concentrated on a PorapackQ or ODS trap and subsequently eluted with methanol. The influence of extraction variables such as modifier content, pressure, temperature, flow-rate, extraction time, and collection/elution variables, were studied. Total phenol extracts were determined by using a direct measurement at 270 nm as screening method.