Origin of brown discoloration in the staves of oak used in cooperage – Characterization of two new lignans in oak wood barrels

The isolation and characterization of the lignans from Quercus petraea oak wood are described. This is the first report of isolariciresinol and secoisolariciresinol being detected in oak wood. Lignan trimethylsilyl ether derivatives were characterized by gas chromatography/mass spectrometry. Lyoniresinol lignans (two isomers) are the major lignan in oak wood; isolariciresinol and secoisolariciresinol were identified as minor lignan components. No lignan glycosides were identified in this matrix.The study of ellagitannins fraction by size exclusion chromatography (SEC) from staves presenting diffuse brown marks, and particularly the presence of polymeric ellagitannins fractions and also the presence of lignans permitted to explain the discoloration origin in oak wood for barrel making.