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Journal of Applied Biological Sciences 2 (3): 51-55, 2008
ISSN: 1307-1130, www.nobel.gen.tr
INTRODUCTION
There are more than 500 species of Quercus occurring in
North, Central and South America, Europe, Asia and northern
Africa. They occur in temperate and subtropical ecosystem
and in the tropics at high elevations. Most oaks are trees, but
many are shrubs, and some are little more than sprawling
ground covers. The oaks can be divided into two main groups;
red oak and white oak groups. There are approximately 200
species of red oaks (Quercus, section Lobatae) [1, 2] restricted
to the New World. Jensen [1] included 35 species of red oaks
in “Flora of North America,” north of Mexico. The northern
red oak (Quercus rubra) is a powerful and large deciduous
tree that normally develops a short trunk and round crown.
It sometimes is a dominant species in the forest, but usually
grows in association with other trees of the mixed forest at
low to moderate elevations in northeast and middle America.
Northern red oak is tolerant of urban air pollution and widely
planted as a street tree in the American Northeast and Midwest.
It is an important source of wood products. The acorns of this
species is also valuable food in wild life and human nutrition.
Oak species are characterized by unusually high levels of
morphological variability which often pose serious taxonomic
problems. This variation may be attributed to high intrinsic
levels of genetic variation, phenotypic plasticity and gene
fl ow potential among species [4]. A few molecular genetic
studies have been conducted on their diversity and phylogeny
of red oaks. Guttman and Weigt [5] found most red oak taxa
to be similar in mean number of alleles per locus, percent
polymorphic loci and mean heterozygosity. It was also reported
low levels of genetic differentiation among populations in
Quercus rubra [6] and between species in Wisconsin [7]. In
phylogenetic relationships within subgenus Quercus, individual
gene trees based on chloroplast DNA (cpDNA) restriction
sites, nucleotide sequences of the internal transcribed spacers
(ITS) and nuclear ribosomal DNA repeats were reported to be
complementary in supporting clades that generally correspond
to previously recognized taxonomic groups [8]. On the other
hand, fatty acid profi les in the seed oils have great importance
for chemotaxonomic differentiation in the plant kingdom [9].
Signifi cantly different concentrations, critical values, total
percentages and the relative ratios of saturated and unsaturated
fatty acids were suggested to be valuable tools to segregate
Quercus at the infrageneric level in accord with established
phylogenic associations [10]. Acorn steroids and acorn fatty
acids as biochemical markers provided strong evidence
to support fi eld observations of hybridization between Q.
wislizeni and Q. agrifolia and additionally indicated signifi cant
differentiation between Sierra Nevadan and coastal populations
of the former species [11]. Acorns were a staple food for many
people until after AD 1900 in Europe, Asia, North Africa,
the Middle-East, and North America and occured in the early
town sites in the Zagros Mountains and at Catal Huyuk (6000
BC) [3]. The acorn is low in protein and rich in fat and starch
[12] and a traditional product in the Spanishs Mediterranean
diet used in ice creams and other desserts and liqueurs [13].
Valuable quantities of essential amino acids compared to daily
requirements of FAO (Food and Agriculture Organization)
were also reported in Turkish Quercus acorns [14]. Although
great diversity of Quercus, a limited number of taxon (ca.40)
were examined for quantitative compositions of acorn oils
as recorded in SOFA (Seed Oil Fatty Acids), and stressed the
utility as potential alternative food reserves for crude vegetable
oil.
Apart from one unpublished study recorded in SOFA, no
paper was reported with respect to fatty acid concentrations of
Fatty Acid Composition in the Acorn Oil of Quercus rubra L. Cultivated in
NW Turkey
Tamer ÖZCAN*
Department of Biology, Division of Botany, Faculty of Science, Istanbul University, 34460 Istanbul, Turkey
* Corresponding Author Received: March 03, 2008
e-mail: tameroz@istanbul.edu.tr Accepted: April 30, 2008
Abstract
Total oil and fatty acid composition in the acorns of Quercus rubra L. was analysed in this study. Total percentage of acorn oil
found at the level of 7,41% (dry wt.%). The major fatty acids were oleic (48,25%), linoleic (35,61 %), and palmitic acids (11,22%)
respectively. Lower levels in stearic (1,49%) and α-linolenic acids (0,74%) were quantifi ed. The other fatty acids were also detected
in minor concentrations. Total percentage of the mono-unsaturated fatty acids was 49,19%. Poly-unsaturated (36,38%) and saturated
fatty acids (14,05%) showed relatively lower concentrations. Total unsaturated fatty acids observed at very high level (85,57%).
The ratio of unsaturated fatty acids to saturated ones was also relatively high (6:1). Characteristic fatty acid pattern in this species
may be useful in taxonomy of Quercus as additional chemometric data. The acorn oil contained valuable concentration of linoleic
acid as an essential fatty acid with respect to dietary reference intakes of FAO and may be evaluated as alternative co-product for
industrial purposes.
Key words: Quercus rubra, acorn oil, fatty acid, taxonomy, nutrition
T. Özcan / JABS, 2 (3): 51-55, 2008
52
the acorns in this species. A cultivated specimen of Quercus
rubra as an exotic species for actual fl ora of Turkey was analysed
in order to observe ecological variations of fatty acid quantities
of the acorn oil compared to the values of native population in
North America and the utility of these parameters in taxonomy
of this species in addition to nutritional product potential.
MATERIALS AND METHODS
Acorn specimens of Quercus rubra were picked at random
in the ripened stage from various branches of the cultivated tree
in Demirköy placed in Istranca mountain of Europe-in-Turkey.
Collected specimens kept in cool were transported to the
laboratory in polypropylene bags and packed in glass vessels
in the deep-freezer (-18 °C) until the analysis carried out. Air
dried mature acorn samples were dehulled, and the kernels
(dicotyledons) were ground into meal and homogenized with
pestle and mortar. Total oil content was detected with ‘‘Tecator
Soxtec System HT’’. Powdered material (3 g) from each sample
was added to oil in cartridge (W1) with 25–50 ml ether into a
weighted extraction pot (W2). Extraction was carried out for
15 min with rinsing for 30–45 min. The extracted seed meals
were air dried to remove traces of solvent and oven dried at 100
°C. The pots were cooled in a dessicator and weighed (W3).
The following equation was used to calculate percentages of
the oil: Oil % = [(W3-W2)/W1] x 100. The oil was transferred
into glass sealed amber dark bottles, capped and stored at
–18 °C until analyzed. The methyl esters of 33 fatty acids
(FAMEs) were prepared from the acorn oil and determined by
gas chromatography (GC) according to the method described
by Slover and Lanza [15], and Alasalvar et al. [16]. FAMEs
prepared using BF3 (20%) in methanol were extracted with n-
hexane and analyzed by GC. Sample (1 μl) was injected into
a Supelcowax 10 column (60 m × 0.25-mm i.d., 0.25-μm fi lm
thickness; Supelco, Bellefonte, PA) coated with poly- (ethylene
glycol). The column was connected to a Hewlett–Packard
5890 Series II (Little Falls, Willmington, DE) GC equipped
with a fl ame-ionization detector. The injector and detector
temperatures were 200 and 250 °C, respectively. Helium as the
carrier gas was used at a fl ow rate of 1.5 ml/min. The oven
temperature was programmed as follows: 180 °C for 2 min,
increased to 200 °C at 2 °C/min, held at 200 °C for a further 10
min, and then increased to 215 °C at 2 °C/min and kept there
for 10 min. Identifi cation and quantifi cation of fatty acid methyl
esters were accomplished by comparing the retention times of
the peaks with authentic standards. All chemical reagents and
standards were obtained from Sigma–Aldrich– Fluka Co. Ltd.
Each value of the experimental results is the average from
dublicate determinations.
RESULTS
High level of total oil (7,41%) was examined in the acorns.
The compositions and percentages of the fatty acids were
documented in the fi gure and table (Fig 1 and Table 1). The
major fatty acids were oleic (48,25%), linoleic (35,61 %), and
palmitic acids (11,22%) respectively. Stearic (1,49%) and α-
linolenic acids (0,74%) exhibited the lower levels. The other
fatty acids were also quantifi ed below 1%.
Figure 1. GC spectrum of the fatty acids in the acorn oil of
Quercus rubra L.
Highest total percentages were observed in the mono-
unsaturated fatty acids (49,19%). Poly-unsaturated (36,38%)
and saturated fatty acids (14,05%) showed relatively lower
concentrations. Unsaturated fatty acids in total was also found
at very high level in the acorn oil (85,57%). Characteristically
proportions between unsaturated and saturated fatty acids were
observed. The proportions of mono- (3,50), poly- (2,59) and
total unsaturated fatty acids (6,09) to saturated fatty acids in
total were determined at considerably high level.
Table 1. Total oil percentages, fatty acid compositions and
some of their ratios in the acorns of Quercus rubra
species
Q.rubra
(Subgen.
Erythrobalanus
sect.lobatae)
C6:0 Caproic acid 0
C8:0 Caprylic acid 0
C10:0 Capric acid 0
C11:0 Undecanoic acid 0
C12:0 Lauric acid 0,020
C14:0 Myristic acid 0,150
C15:0 Pentadecanoic acid 0,037
C16:0 Palmitic acid 11,227
C16:1 Palmitoleic acid 0,247
C17:0 Heptadecanoic acid 0,050
C17:1cis-10-Heptadecanoic acid 0,065
C18:0 Stearic acid 1,497
C18:1n9t Elaidic acid 0,021
C18:1n9c Oleic acid 48,258
C18:2n6t Linolelaidic acid 0
C18:2n6c Linoleic acid 35,616
C18:3n6 Gamma linolenic acid 0
C20:0 Arachidic acid 0,600
C18:3n3 Alpha linolenic acid 0,742
C20:1n9 cis-11-Eicosenoic acid 0,599
C21:0 Henicosanoic acid 0,052
C20:2 cis-11,14-Eicosadienoic acid 0,027
C20:3n3 cis-11,14,17-Eicosatrienoic acid 0
T. Özcan / JABS, 2 (3): 51-55, 2008 53
C22:0 Behenic acid 0,251
C22:2 cis 13,16 Docosadienoic 0
C20:4n6 Arachidonic acid 0
C22:1n9 Erucic acid 0
C23:0 Tricosanoic acid 0,043
C22:2cis-4,7,10,13,16,19-Docosahexaenoic
acid 0
C20:5n3cis-5,8,11,14,17-Eicosapentaenoic
acid 0
C24:0 Lignoceric acid 0,125
C24:1n9 Nervonic acid 0
C22:6n3 cis-4,7,10,13,16,19-
Docosahexaenoic acid 0
Undetermined % 0,373
Saturated % 14,052
Mono unsaturated % 49,190
Poli unsaturated % 36,385
Total unsaturated 85,575
Mono unsaturated /Saturated 3,500
Poli unsaturated /Saturated 2,589
Total unsaturated /Saturated 6,089
Mono unsaturated / Poli unsaturated 1,351
Linoleic acid / α-linolenic acid 48,000
Total oil amount % 7,41
Linoleic acid (AIs for life stage groups)
g/day 4,4-17
α-linolenic acid (AIs for life stage
groups) g/day 0,5-1,6
Each value of fatty acid concentrations is the average of
dublicate determinations
Higher concentration of mono-unsaturated fatty acids than
poly-unsaturated fatty acids was detected at the ratio of 1,35%.
Calculated some proportions of fatty acids refl ect more stable
pattern than individual fatty acid concentrations. Linoleic and
α-linolenic acid as essential fatty acids exhibited valuable
concentrations with respect to adequate intakes (AIs) of fatty
acids according to dietary refence intakes (DRIs) for different
life stage groups [17]. Higher proportion of linoleic acid to α-
linolenic acid (48,0) than the ratios of adequate intakes (AIs)
reported in DRIs was found. Investigated major fatty acids,
total ratios of saturated and unsaturated fatty acids and their
some relative proportions represent characteristic pattern as
additional chemometric data in the species concept of Quercus
rubra.
DISCUSSION
Red oak grows best in Euro-Siberian region of Turkey
presenting suitable conditions for its cultivation. The
distinguishing characteristics include an acorn cup that is fl at,
thin and papery leaves and winter buds on twig tips hairless and
not angled. It isn’t always possible to identify oaks to species
with complete certainty. Many other species of oaks are similar
to northern red oak, and several species are known to hybridize
with it. But, no hybrids were reported between Lepidebalanus
(white oaks) and Erythrobalanus (black and red oaks) [18].
Compositions and concentrations of fatty acids stored in seeds
express the characteristic patterns in biochemical systematic at
different plant groups [9]. Fatty acid pattern of the acorn oil of
Quercus rubra as additional chemotaxonomic data may refl ect
its genotype, apart from environmental conditions. It was
reported that most genetic variation and isoenzyme diversity
in red oaks was contained within the population. However, low
estimates of genetic diversity were reported between populations
of red oaks [19, 20]. On the other hand, the range of the areals
for any species may account for the reason of biochemical
polymorphism derived from both original genotypes and the
ecological factors. Some differences in fatty acid patterns may
be the result of disjunct distribution of the plant populations
indicating genetical divergency. In general, parallel results
with current study were announced in red oak group which
contain decreasing levels of major fatty acids; oleic, linoleic
and palmitic acids respectively [3,11,21,22]. Obtained results
for fatty acid concentrations and their some proportions are
generally correspond with the values from section Cerris
Loudon as red oak group in Flora of Turkey, apart from
Quercus cerris. Other sections exhibited completely different
profi les of the fatty acids [10]. Such similar patterns may
indicate the synapomorphy explaining phylogenetic relations
and common pathways involved in the biosynthesis and
accumulation of the fatty acids. Acorn fatty acids as diagnostic
parameters could also signifi cantly separated related species
from each other [11]. But, some ecological parameters should
be considered. A separation of xeric zone populations from
mesic populations based on fatty acid profi les was reported in
13 natural populations of Austrocedrus chilensis from Andean
Chile and Argentina. These differences were associated with a
greater abundance of C20 unsaturated acids in the mesic group
[23]. Signifi cant differences between the fatty acid results were
also found in different years for each species [24]. In general,
fatty acid results in the acorn oil of Quercus rubra from two
different continent are in good agreement. Our results from
cultivated specimen in Turkey are correspond with the fi ndings
of Ivanov and Aitzetmüller obtained from native population
of Quercus rubra in North America (SOFA data, unpublished
results, 1998) for oleic (63,80%), linoleic (18,40%), palmitic
(11,0%) and stearic acids (1,60%). But, lower level for oleic
(48,25%), higher concentration for linoleic (35,61%) and
similar values for palmitic (11,22%) and stearic acid (1,50%)
were determined in this study. Unsaturated fatty acids exhibited
some variations between two studies, while strictly agreement
present in saturated fatty acids. More variable quantities in
unsaturated fatty acids and consistent levels of saturated
fatty acids were also examined for two varieties of Quercus
cerris collected from three different populations in Turkey.
Signifi cantly differences at sectional level of Quercus were
reported for palmitic, stearic and oleic acid concentrations. In
addition, sectional differences were also signifi cant for some
relative concentrations of the fatty acids [10]. Saturated fatty
acids may be more stable parameters which are relatively little
affected from ecological conditions and determined primarily
with genetical factors.
The acorns of Quercus are rich in total oil. Some varieties
contain more than 30 percent oil, equal or greater than the best oil
olives [25, 26]. As reported in Q. rubra, acorn dominated diets
high in metabolizable energy provide optimal fat deposition for
winter survival in deers [27]. Considerably high level of total oil
in the acorns of Q. rubra (7,41%) was quantifi ed in this study.
T. Özcan / JABS, 2 (3): 51-55, 2008
54
The percentage of total fat may exhibit some variation with
respect to environmental factors. In cold climate conditions,
the higher level of seed lipid contents, and decreasing levels of
seed oils correlated with dry seasons were reported for different
plant groups exhibiting constant profi les of fatty acid quantities
in general [28, 29]. Such differences in total oil contents may
be partly explained with different geographical, ecological
and growing conditions in addition to ripening stages of the
seeds. It was reported that temperate variety oils are less
saturated due to a natural selection in northern latitudes for oils
with a higher energy storage capacity or which remain liquid
at a lower temperature [30]. Considering as a biomonitor or
marker specimen, our observations on this species provide the
information for the range of variation of fatty acid composition
in the acorn oils based on geographical and growing conditions
in order to evaluate the results for chemotaxonomic utility as
stable parameters. In general, parallel fi ndings with the native
population of this species growing in two different continent
of Holoarctic region may primarily indicate consistent and
genotypic characteristic of fatty acid pattern in the acorn oil.
Data reported by Garcia and Buron [32] show that acorn
oil should be classifi ed as a non-drying oil, with its density
similar to peanut oil, its viscosity similar to corn, sunfl ower
and soybean oils, and with many other physical and chemical
parameters similar to olive oil. The unsaturated/saturated ratio
in the acorns of Quercus rubra was relatively high, at 6:1,
and the relatively high content of linoleic acid as essential
fatty acid (35,61%) makes acorn oil of this species especially
prone to oxidation. However, this profi le may have nutritional
implications and benefi cial effects in the prevention of coronary
heart disease. Actually, Portuguese legislation [31] includes the
acorn oil in the category of directly alimentary oils, although no
industrial oil is produced. FA profi le of Quercus rubra was very
similar to those of other edible vegetable oils such as peanut,
olive, hazelnut, avocado, tea seed, and kapok seed. This species
can be planted for use as food, in addition to valuable feed for
domestic animals, birds and wildlife. In suitable conditions,
the yield of acorns per acre compares well with grains and
acorn production can be very high, with yields of more than
5,280 kg/ha [3]. High acorn yields can be maintained on hilly
lands where annual grain crops cause severe soil erosion. The
production of acorn oil could add value to an underutilized
agricultural product. Turkey that is in the same latitudes with
the native populations of Quercus rubra exhibits suitable
climatic conditions for the cultivation of this species. High
ecological tolerance as observed with high acorn production
in the northern district of Europe-in-Turkey may imply its
alternative utility in forestry.
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