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 degrees C) has been tested. The evolution of the same compounds in boiling methanol (65 degrees 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 degrees C and 94.1% for epicatechin at 100 degrees C). Phenolic compounds kept at the boiling point of methanol (65 degrees 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.