Abstract
The bark from Quercus faginea mature trees from two sites was chemically characterized for the first time. The barks showed the following composition: ash 14.6%, total extractives 13.2%, suberin 2.9% and lignin 28.2%. The polysaccharides were composed mainly of glucose and xylose (50.3% and 35.1% of all monosaccharides respectively) with 4.8% of uronic acids. The suberin composition was: ω-hydroxyacids 46.3% of total compounds, ɑ,ω-alkanoic diacids 22.3%, alkanoic acids 5.9%, alkanols 6.7% and aromatics 6.9% (ferulic acid 4.0%). Polar extracts (ethanol-water) had a high phenolic content of 630.3 mg of gallic acid equivalents (GAE)/g of extract, condensed tannins 220.7 mg of catechin equivalents (CE)/g extract, and flavonoids 207.7 mg CE/g of extract. The antioxidant activity was very high corresponding to 1567 mg Trolox equivalents/g of extract, and an IC50 of 2.63 μg extract/ml. The lipophilic extracts were constituted mainly by glycerol and its derivatives (12.3% of all compounds), alkanoic acids (27.8%), sterols (11.5%) and triterpenes (17.8%). In view of an integrated valorization, Quercus faginea barks are interesting sources of polar compounds including phenols and polyphenols with possible interesting bioactivities, while the sterols and triterpenes contained in the lipophilic extracts are also valuable bioactive compounds or chemical intermediates for specific high-value market niches, such as cosmetics, pharmaceuticals and biomedicine.
Highlights
The Quercus faginea Lam. (Portuguese oak) species is native to the Western Iberian Peninsula, and the North African countries of Morocco, Tunisia and Algeria, where it coexists with other oaks such as Q. ilex L., Q. suber L., Q. pyrenaica Willd., and Q. robur L
The bark samples were obtained from Quercus faginea trees selected from two stands located in the region of the species natural distribution in Portugal
The number of samples used in these studies is small and general conclusions have to be made cautiously, the results suggest a possible relation between tree age and suberin chemical composition: in older trees suberin is constituted by higher content of mid-chain substituted fatty acids, leading to a spatially lesscompact macromolecular structure [61]
Summary
The Quercus faginea Lam. (Portuguese oak) species is native to the Western Iberian Peninsula, and the North African countries of Morocco, Tunisia and Algeria, where it coexists with other oaks such as Q. ilex L., Q. suber L., Q. pyrenaica Willd., and Q. robur L. Its distribution has become fragmented in the last centuries [1], and there are concerns on a future area reduction with warming and reduced rainfall trends, since drought is the main limiting factor of subMediterranean oaks [2], and of Q. faginea [3,4]. Chemical composition of barks from Quercus faginea tree. The third author acknowledges a post-doc scholarship by FCT (SFRH /BPD/ 97970/2013)
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