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The Influence of Solvent and Extraction Time on Yield and Chemical Selectivity of Cuticular Waxes from Quercus suber Leaves
Publication . Simões, Rita; Miranda, Isabel; Pereira, H.
The cuticular lipid compounds, usually named cuticular waxes, present in the cuticular
layering of Quercus suber adult leaves were extracted with solvents of different polarities (n-hexane,
dichloromethane and acetone) and analysed by GC–MS. Q. suber leaves have a substantial cuticular
wax layer (2.8% of leaf mass and 239 g/cm2), composed predominantly by terpenes (43–63% of all
compounds), followed by aliphatic long chain molecules, mainly fatty acids, and by smaller amounts
of aliphatic alcohols and n-alkanes. The major identified compound was lupeol (1.2% of leaves in
n-hexane extract). The recovery and composition of cuticular lipids depended on the solvent and
extraction time. The non-polar or weak polar solvents n-hexane and dichloromethane extracted
similar lipid yields (77% and 86% of the total extract, respectively) while acetone solubilised other
cellular compounds, namely sugars, with the lipid compounds representing 43% of the total extract.
For cuticular lipids extraction, solvents with a low polarity such as n-hexane are the more suitable
with an adequate extraction duration, e.g., n-hexane with a minimum extraction of 3 h
Effect of Seasonal Variation on Leaf Cuticular Waxes’ Composition in the Mediterranean Cork Oak (Quercus suber L.)
Publication . Simões, Rita; Miranda, Isabel; Pereira, Helena
Quercus suber L. (cork oak) leaves were analyzed along one annual cycle for cuticular wax
content and chemical composition. This species, well adapted to the long dry summer conditions
prevailing in the Mediterranean, has a leaf life span of about one year. The cuticular wax revealed a
seasonal variation with a coverage increase from the newly expanded leaves (115.7 g/cm2 in spring)
to a maximum value in fully expanded leaves (235.6 g/cm2 after summer). Triterpenoids dominated
the wax composition throughout the leaf life cycle, corresponding in young leaves to 26 g/cm2
(22.6% of the total wax) and 116.0 g/cm2 (49% of the total wax) in mature leaves, with lupeol
constituting about 70% of this fraction. The total aliphatic compounds increased from 39 g/cm2
(young leaves) to 71 g/cm2 (mature leaves) and then decreased to 22 g/cm2 and slightly increased
during the remaining period. The major aliphatic compounds were fatty acids, mostly with C16
(hexadecanoic acid) and C28 (octacosanoic acid) chain lengths. Since pentacyclic triterpenoids are
located almost exclusively within the cutin matrix (intracuticular wax), the increase in the cyclicto-
acyclic component ratio after summer shows an extensive deposition of intracuticular waxes in
association with the establishment of mechanical and thermal stability and of water barrier properties
in the mature leaf cuticle
Insights into cork weathering regarding colour, chemical and cellular changes in view of outdoor applications
Publication . Miranda, Isabel; Lourenço, Ana; Simões, Rita; Athayde, João; Pereira, Helena
A comprehensive analysis of outdoor weathering and soil burial of cork during 1-year experi-
ments was carried out with measurements of CIELAB color parameters, cellular observa-
tions by scanning electron microscopy, and surface chemical features analysed by ATR-
FTIR and wet chemical analysis. Cork applied in outdoor conditions above and below
ground retained its physical structure and integrity without signs of deterioration or fractur-
ing. The cellular structure was maintained with some small changes at the one-cell layer at
the surface, featuring cellular expansion and minute cell wall fractures. Surface color and
chemistry showed distinct results for outdoor exposure and soil burial. The weathered cork
surfaces acquired a lighter color while the soil buried cork surfaces became darker. With out-
door weathering, the cork polar solubles increased (13.0% vs. 7.6% o.d. mass) while a sub-
stantial decrease of lignin occurred (about 28% of the original lignin was removed) leading
to a suberin-enriched cork surface. The chemical impact on lignin is therefore responsible
for the surface change towards lighter colors. Soil-burial induced hydrolysis of ester bonds
of suberin and xylan, and the lignin-enriched cork surface displayed a dark brown color.
FTIR and wet chemical results were consistent. Overall cork showed a considerable struc-
tural and physical stability that allows its application in outdoor conditions, namely for build-
ing fac¸ades or other surfacing applications. Architects and designers should take into
account the color dynamics of the cork surfaces.
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Fundação para a Ciência e a Tecnologia
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OE
Número da atribuição
PD/BD/128259/2016