Stability of phenolic compounds during extraction with superheated solvents

The stability of nine phenolic compounds in the extraction with superheated methanol at different temperatures (40, 50, 100 and 150°C) has been tested. The evolution of the same compounds in boiling methanol (65°C) in contact with air was also determined. All the assayed phenolic compounds were stable under the extraction conditions with the exception of catechin and epicatechin (recoveries: 87.4% for catechin and 86.0% for epicatechin at 150°C and 94.1% for epicatechin at 100°C). Phenolic compounds kept at the boiling point of methanol (65°C) showed lower recoveries: gentisic acid (85.5%), syringic aldehyde (92.8%), catechin (63.7%) and epicatechin (63.4%). Extraction with superheated solvents was also applied to the extraction of phenolic compounds from solid wastes of the winemaking process.