Structural Elucidation of Suberin from the Bark of Cultivated Willow (Salix sp.)

Although extractives have been symbolized as major bioactive pharmacological compounds from Salix (Salicaceae) bark, we speculated that these pharmaceutical effects cannot be solely attributed to phenolic components and their derivatives, but the long-chain suberin acids also contribute to their therapeutic effects. Hence, isolation and deconstruction of suberin were conducted, for the first time, to enrich our knowledge about the macromolecular components at the cell wall of willow bark. Saponification was adopted to obtain suberin extracts at a yield of approximately 5 wt % based on the bark of the studied hybrids. Gas chromatography-mass spectrometry allowed qualification and quantification of 23 compounds from the released suberin monomers, from which fatty acids represented majority of the isolated suberin, namely, fatty acid methyl esters (C17-C19); mono-carboxylic acid (C7-C16); alpha, omega-dicarboxylic acid (C7-C16); and omega-hydroxy long-chain fatty acids (C16-C22). Additionally, the lipophilic extractive was dominated by piceol, heptacosane, β-sitosterol, and fatty acids (C16-C28) from the studied hybrids. These findings could boost our integrative approach toward full valorization of willow bark.