Use of superheated liquids for the extraction of non-volatile compounds from wood: liquid chromatography studies

A study of the extraction of non-volatile compounds from oak wood using superheated water–ethanol mixtures ranging from 10 to 60% ethanol is reported. Identification and characterization of the extracted compounds have been made by high performance liquid chromatography. The extraction has been performed using the static mode by single or repetitive cycles. The variables affecting the extraction process have been studied and their optimum values established (extraction time: 50 min; pressure: 40 atm; extraction temperature: 180 °C). The study allows comparing the non-volatile polyphenol fractions obtained in this way with those present in commercial samples with fully agreement between them. In addition, the method makes possible manipulation of the extract composition by changing the working pressure, temperature and water–ethanol ratio.