Valorisation of bark lipophilic fractions from three Portuguese Salix species: A systematic study of the chemical composition and inhibitory activity on Escherichia coli

Abstract

Salix (Salicaceae) species bark extracts are traditionally consumed due to their anti-inflammatory and analgesic benefits, mainly attributed to phenolic compounds. However, this biomass could be further exploited calling upon other extractive components, namely the lipophilic fraction. Hence, the present study highlights, for the first time, the chemical characterisation and the inhibitory effect of S. viminalis L., S. atrocinerea Brot. and S. fragilis L. bark lipophilic dichloromethane extracts against the Gram-negative bacterium Escherichia coli. Gas chromatography-mass spectrometry allowed the identification and quantification of 63 compounds, from which 36 were reported for the first time in these Salix species, namely 15 aromatic compounds, 4 fatty acids, 4 long chain aliphatic alcohols, 1 diterpene, 4 pentacyclic triterpenes, 4 tocopherols, 3 long chain aliphatic aldehydes and 1 sterol. Long chain aliphatic aldehydes represent the prevalent family, with triacontanal as the major component in S. fragilis L. and S. atrocinerea Brot. barks. Additionally, β-sitosterol was the major component identified in S. viminalis L. bark lipophilic extract, followed by lupeol. This last extract exhibited the highest inhibitory effect against E. coli viability, being probably related with these bioactive components. In contrast, aromatic compounds were detected at high abundances in S. atrocinerea Brot. and S. fragilis L. barks, with piceol as the predominant component. These findings can contribute to valorise bark of the three endogenous Portuguese Salix species, based on their chemical composition and biological properties.