Characterization of flavan-3-ols in seeds of grape pomace by CE, HPLC-DAD-MSn and LC-ESI-FTICR-MS

► The winemaking process do not give rise to (-)-catechin and (+)-epicatechin enantiomers. ► (epi)Catechin-ethyl trimers and tetramers have been reported in winery byproducts for the first time. ► LC-ESI-FTICR-MS turns out to be an appropriate method to analyze the complex phenolic composition of grape seeds.