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Quercus rotundifolia bark as a source of polar extracts: structural and chemical characterization
Publication . Sousa, Vicelina; Ferreira, Joana P.A.; Miranda, Isabel; Quilhó, Teresa; Pereira, Helena
Quercus rotundifolia bark was studied regarding anatomical, chemical, and antioxidant
properties from trees in two sites in southern Portugal and are here reported for the first time. The
general structure and anatomy of Q. rotundifolia bark showed a rhytidome with sequential undulated
and anastomosed periderms with a small proportion of cork, while the phloem included broad rays
with strong cell sclerification, groups of sclereids with embed large prismatic crystals, and abundant
druses in parenchyma cells. The mean chemical composition was 15.5% ash, 1.6% dichloromethane
extractives, 6.4% ethanol and 9.3% water extractives, 3.0% suberin, 30.5% total lignin, and 33.8%
carbohydrates. Carbohydrates included mainly glucose (50.7% of total monomers) and xylose
(23.8%), with uronic (3.0%) and acetic acids (1.0%). Suberin was mainly composed of !-hydroxyacids
(48.0% of all compounds) and ,!-diacids (19.5%). The main compounds found in the lipophilic
extracts were triterpenes (43.6%–56.2% of all compounds) and alkanoic acids (32.7%–41.7%). Phenolic
content was high especially in the ethanol extracts, ranging from 219.5–572.9 mg GAE/g extract and
comprising 162.5–247.5 CE/g extract of flavonoids and 41.2–294.1 CE/g extract of condensed tannins.
The extracts revealed very good antioxidant properties with IC50 values of 4.4 g ethanol extract/mL
and 4.7 g water extract/mL. Similar anatomical, chemical, and antioxidant characteristics were
found in the bark from both sites. The high phenolic content and excellent antioxidant characteristics
of polar extracts showed holm oak barks to be a promising natural source of antioxidants with
possible use in industry and pharmaceutical/medical areas
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Fundação para a Ciência e a Tecnologia
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OE
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37774