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Chemical Papers 63 (4) 406–413 (2009)
DOI: 10.2478/s11696-009-0035-5
ORIGINAL PAPER
Chemical evaluation of seeded fruit biomass of oil pumpkin
( L. var. )
Zuzana Košťálová, Zdenka Hromádková*, Anna Ebringerová
Institute of Chemistry, Center for Glycomics, Slovak Academy of Sciences, Dúbr a vská cesta 9, 845 38 Br atislava, Slovakia
Received 18 September 2008; Revised 7 November 2008; Accepted 11 November 2008
Oil pumpkin (Cucurbita pepo L. var. Styriaca) is an economically important horticultural plant
cultivated for oil production. After harvesting seeds, the residual biomass has a limited application
and is usually left in the field. An experimental study was performed to ev aluate the chemical
composition of the seeded fruit oil pumpkin biomass (OP) dried by solven t-exchange using ethanol.
The sugar composition of polysaccharides obtained by sequential extraction with water and dilute
alkali indicated the prevalence of pectic polysaccharides. Hemicelulloses were released in higher
amounts in the alkaline step. The chemical composition of OP and its individual tissues (peel,
flesh and hairy flesh) was in vestigated and compared to the corresponding preparations of standard
pumpkin (SP, Cucurbita pepo L.). The content of components (on ov en-dry basis), calculated from
the analysis data of the individual tissues, was estimated for OP: 7.9 % ash, 7.6 % Klason lignin,
19.3 % pectin (as uronic acids), 34.1 % neutral carbohydrates, and 27.4 % α-cellulose and for SP:
6.4 % ash, 4.0 % Klason lignin, 20.9% pectin (as uronic acids), 38.1% neutral carbohydrates, and
29.2 % α-cellulose, respectively. The OP biomass showed a higher proportion of hemicelluloses.
c
2008 Institute of Chemistry, Slov a k Academy of Sciences
Keywords: Cucurbita pepo L. var. Styriaca, seeded pumpkin fruit, polysaccharides, pectin
Introduction
During the last decades, great attention has been
given to the concept of sustainable economic systems
including the valorization of local biomass. Agricul-
tural byproducts are cheap and abundant lignocellu-
losic feedstocks for the production of polysaccharide-
based materials as well as of antioxidants and other
compounds used in food, medicine and other areas.
Pumpkin (Cucurbita pepo L. var. Styriaca) is an eco-
nomically important horticultural plant cultivated for
oil production in Slovakia. This hull-less seed pumpkin
variety discovered in the late 19th Century (Teppner,
2000) is a spontaneous mutant of standard pumpkin
(Cucurbita pepo L.). After harvesting seeds, the resid-
ual biomass has a limited application and is usually
left in the field.
Pumpkin has been cultivated throughout the world
as vegetable as well as for medical purposes. Its phar-
macological activities comprising antidiabetic, antihy-
pertensive, antitumor, antimutagenic, immunomodu-
lating, antibacterial, antihypercholesterolemic, intesti-
nal antiparasitic, antalgic, and antiinflammation ef-
fects, and utilization possibilities of various pumpkin
species have been reported (Fu et al., 2006; Esuoso et
al., 1998). Important physiological effects of pump-
kin fruit and seeds are connected with the present
proteins, oil and antioxidants (Fahim et al., 1995;
Murkovic et al., 2002), and the cell wall polymers con-
stituting the dietary fiber components (Essien et al.,
1992; Ratnayake et al., 1999; Li et al., 2005; Fu et
al., 2007; de Escalada Pla et al., 2007). Recent studies
werefocusedontheextraction and characterization
of pectin-rich fiber products isolated from pumpkin
(Curcubita moschata) (de Escalada Pla et al., 2007),
and of pectins from other pumpkin species (Fu et al.,
2007; Shkodina et al., 1998; Jun et al., 2006). Their
biological activity (Jun et al., 2006), viscosity and
gelling properties (Evangeliou et al., 2005; Ptitchkina
et al., 1994), and applicability as bread making addi-
*Corresponding author, e-mail: chemhrom@savba.sk
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tive (Ptitchkina et al., 1998) were also explored. The
studies on pumpkin fruits are non-systematic as the
concerned texture changes during storage and cook-
ing of C. maxima (Ratnayake et al., 1999), and chem-
ical and biochemical changes of C. moschata affected
by osmotic stress (de Escalada Pla et al., 2005). The
bioactive materials of pumpkins were suggested to be
polysaccharides, including protein-bound polysaccha-
rides (Fu et al., 2006, 2007). In addition, pumpkin
polysaccharides were reported to have significant an-
tioxidant potential (Fu et al., 2006). From this point of
view, phenolic substances such as phenolic acids and
lignin, which might be covalently linked to cell wall
pectins and hemicelluloses, are of great importance
(Oosterveld et al., 2000).
Among the various Cucurbita species, there are
only a few reports on C. pepo and its hull-less seed mu-
tants dealing with their history, histology, and genet-
ics of the whole plants (Teppner, 2000) and their seed
coat (Stuart & Loy, 1983; Zraidi et al., 2003). Chemi-
cal composition has only been reported for their seed
coats (Stuart & Loy, 1983), and the phenolics and cell
wall polysaccharides from pumpkins (Cucurbita sp.)
were studied to evaluate the fruit product authenticity
(Kurz et al., 2008). In continuation of our studies con-
cerning the exploitation of lesser-known and underuti-
lized agricultural plants, the aim of the present work
was to create a sound basis for future technological ap-
plications of the fruit biomass from oil pumpkin, par-
ticularly the non-cellulosic polysaccharides. For this
purpose, chemical composition of the seeded oil pump-
kin biomass and of its different tissues was studied and
compared to those that of the standard pumpkin tis-
sues. Emphasis has been put on the pectic polysaccha-
rides and hemicelluloses as well as on the associated
phenolic components.
Experimental
Standard pumpkin (Cucurbita pepo L.) and hull-
less seed oil pumpkin (Cucurbita pepo L. var.Styri-
aca) were harvested in September 2005 at the local
fields belonging to the scholar enterprise Kolíňany in
Kolíňany (Slovakia). Gallic acid and d-galacturonic
acid were obtained from Fluka (Germany). All other
chemicals used in this study were of analytical grade.
The citrus pectate and methyl esterified citrus pectin
(DE 20 %) used as standards were prepared and do-
nated by Dr. A. Malovíková (Institute of Chemistry,
Slovak Academy of Sciences, Bratislava, Slovakia).
Fresh fruits of standard pumpkin (SP) and oil
pumpkin (OP) were cleaned with tap water and then
rinsed with distilled water. After halving the fruits,
the seeds were carefully removed and the resulting
biomass of SP and OP were grated into small pieces
(0.6–0.8 mm). The grated OP was dewatered by: (i)
drying on air at 24
◦
C for 2 days yielding air-dried
biomass (DOP) and (ii) the solvent exchange method
using ethanol to remove water from OP. To the OP
biomass, containing 90 % of water, 95 % ethanol was
added and after 2.5 h, the ethanol–water extract was
decanted. To the residue, another portion of 95 %
ethanol was added and after 3 h, the suspension was
decanted again. The insoluble fiber residue and solu-
tions from decantation were filtrated. After the last
treatment, the insoluble fiber mass was dried on air
yielding ethanol-dried biomass (EOP). The filtrate
and decanted solutions were collected and evaporated
under vacuum at 40
◦
C yielding the ethanol-soluble
fraction which was further dialyzed in cellulose tubing
(MWCO 12.4 kg mol
−1
, Sigma–Aldrich). The reten-
tate was lyophilized yielding fraction of EsOPD. This
fraction was further separated into water-soluble (ws-
EsOPD) and insoluble parts (wis-EsOPD) by a disso-
lution of EsOPD (0.2 g) in 10 mL of distilled water at
24
◦
C for 3 h and a following centrifugation at 12000
min
−1
for 7 min. Both fractions were lyophilized.
Distilled water (35 mL) was added to EOP (0.5 g)
and left to soak overnight at 24
◦
C followed by stir-
ring for 1 h at 35
◦
C. The suspension was subjected
to centrifugation at 12000 min
−1
for 7 min. The su-
pernatant was dialyzed using a cellulose membrane
(MWCO of 12.4 kg mol
−1
, Sigma–Aldrich) against
distilled water to a constant conductivity value of the
diffusate which was lyophilized yielding the water-
soluble fraction EOP-W. The water-insoluble pump-
kin residue was further extracted with 1 % NaOH (31
mL) for 1 h at 60
◦
C under stirring. The alkali-insoluble
residue (EOP-R), separated from the extract by cen-
trifugation, was acidified with acetic acid extensively
washed with distilled water and oven-dried at 105
◦
C
for 3 h. The alkaline soluble extract was neutralized
with acetic acid to pH approximately 7.3, subjected
to dialysis, and the retentate was lyophilized yielding
the alkali-soluble fraction EOP-A.
From the seeded pumpkin halves of both fruits, the
peel (P) was manually cut off. Then, the mesocarp
tissue – flesh (F) was separated from the endocarp
tissue – hair-like flesh (HF), where the seeds had been
located. The obtained pumpkin tissues were grated
and dried according to procedure (ii). The residual
moisture content of all dried samples was taken as
weight loss after heating at 105
◦
Cfor2h.
Sugar composition analysis of the pumpkin sam-
ples was performed by the two-step acid hydrolysis
(72 % H
2
SO
4
at ambient temperature for 2 h and after
dilution to 4 % H
2
SO
4
for 4 h under reflux). The acid-
insoluble residue obtained by filtration was quantified
gravimetrically as Klason lignin. The polysaccharide
fractions were hydrolyzed with 2 M trifluoroacetic acid
under reflux for 2 h. The sugars released by both
hydrolytic procedures were qualitatively analyzed by
paper chromatography (PC) using systems S
1
ethyl
acetate–pyridine–water (ϕ
r
=8:2:1)andS
2
ethyl
acetate–acetic acid–formic acid–water (ϕ
r
=18:3:1:
4). The neutral sugar composition of hydrolyzates was
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408 Z. Košťálová et al./Chemical Papers 63 (4) 406–413 (2009)
determined by GC of their alditol trifluoroacetates us-
ing a Hewlett–Packard Model 5890. The above men-
tioned methods were described in more details in a
previous paper (Hromádková & Ebringerová, 2003).
The total carbohydrate content (TC) was deter-
mined by a modified version of the phenol–sulfuric
acid method (Rao & Pattabiraman, 1989), which com-
prises also treatment of the aqueous suspension of the
sample with concentrated sulfuric acid. A part of the
hydrolyzate was diluted with distilled water and then
sulfuric acid and phenol were added. Glucose was used
as a standard.
The uronic acid content (UA) was determined us-
ing 3-hydroxybiphenyl as a reagent (Ahmed & Labav-
itch, 2007) and galacturonic acid as a standard.
The content of extractive substances (ES) was de-
termined gravimetrically by Soxhlet extraction with
chloroform–ethanol (ϕ
r
= 2 : 1) for 6 h. The nitro-
gen content was determined using an elemental an-
alyzer Fisons instrument EA1108, and the ash con-
tent was determined gravimetrically by combustion at
850–900
◦
C. The total phenolics content (TP) was de-
termined by the Folin–Ciocalteau assay (Thaipong et
al., 2006) using gallic acid as a calibration standard.
The α-cellulose content was determined by modifica-
tion of the novel hydrolytic technique based on hydrol-
ysis with an acetic acid–nitric acid mixture (Brendel et
al., 2000). This modification introduced a new extrac-
tion step with diluted acetic acid adjusting pH to 2.5
in order to enhance the release of pectic polymers as
well as the centrifugation speed (12000 min
−1
). Spec-
trophotometric measurements were carried out on a
Spectronic 20 Genesis (Rochester, USA) spectrome-
ter. Fourier transform infrared (FTIR) spectra were
obtained on a NICOLET Magna 750 spectrophotome-
ter with a DTGS detector and OMNIC 3.2 software
using 128 scans at the resolution of 4 cm
−1
.Thesam-
ples (2.0 mg) were pressed into KBr pellets (200 mg).
Results and discussion
Effect of the drying method
The effect of drying on the composition of grated
OP biomass was tested using (i) drying on air at
ambient temperature and (ii) solvent exchange with
ethanol (Fig. 1). Analytical data of the obtained sam-
ples are summarized in Table 1. In comparison to the
air-dried biomass (DOP), the ethanol-dried biomass
(EOP) showed a significantly higher content of Kla-
son lignin and higher proportion of glucose, whereas
the content of extractive substances (ES) was similar
and protein content was slightly lower. Glucose repre-
sents mainly cellulose, some amounts might however
originate from the hemicellulose cell wall components
(xyloglucan, glucomannan) (Ebringerová et al., 2005)
as well as from starch found in pumpkins (de Escalada
Pla et al., 2005). It has to be noted that the Klason
Fig. 1. Scheme of drying and isolation of easy extractable non-
cellulosic polysaccharides from the seeded fruit biomass
of oil pumkin (OP).
lignin values are overestimated because proteins, ash
and some phenolics forming acid-insoluble substances
during the hydrolytic step contribute to these values.
As expected, with respect to other reports on pump-
kin fruits (de Escalada Pla et al., 2005, 2007), EOP
is rich in pectic polysaccharides indicated by the high
content of uronic acids consisting predominantly of
galacturonic acid (detected by PC in system S
2
)andof
arabinose and galactose, both constituting the neutral
polysaccharide side chains of the pectin molecule (Vor-
agen et al., 1995). High proportion of xylose in DOP
indicates the presence of xyloglucan, xylan, and/or the
xylogalacturonan component of pectic polymers found
in watermelone (Mort et al., 2002).
Differences in composition of DOP and EOP can
be explained by the removal of aqueous-ethanol sol-
uble compounds (EsOPD) during the ethanol treat-
ment and the following dialysis step. This fraction con-
tained uronic acids (10 %), arabinose, and galactose
as dominating neutral sugars, and minor amounts of
mannose, rhamnose, glucose, and xylose. Its protein
content, estimated from the nitrogen content w(N) =
(6.25 %), was more than three times higher than that
in both DOP and EOP (Table 1). A part of nitro-
gen might belong to polyamines found in the fruit of
normal and a hull-less seed varieties of pumpkin (Be-
zold et al., 2003). The sugar composition indicated
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Tabl e 1 . Effect of drying on the oil pumpkin biomass (OP) dried on air (DOP) and by solvent exchange with ethanol (EOP)
Content, w
i
/%
a
Neutral sugars, x
r
/mole %
Sample
Lignin
b
Ash Protein ES
c
UA
d
Rha Ara Xyl Man Glc Gal
DOP 2.0 7.9 11.3 6.6 14.4 tr 6.3 28.6 3.3 46.5 15.3
EOP 6.8 6.1 8.8 6.9 20.4 tr 4.4 10.9 4.4 75.0 5.3
EsOPD
e
0 nd 35.0 3.6
f
10.1 4.2 37.9 4.1 12.4 5.2 36.2
Analytical data are means of at least three experiments. a)Calculatedonair-drybasis;b) Klason lignin as acid-resistant portion
after hydrolysis; c) substances isolated by chloroform–ethanol extraction; d) uronic acids determined by the 3-hydroxybiphenyl
assay; e) ethanol-soluble fraction from the ethanol drying process after removal of dialyzable substances; f ) total phenolics (TP)
determined by the Folin–Ciocalteau assay; tr – traces detectable by PC, nd – not determined.
Fig. 2. FTIR spectra of (a) oil pumpkin biomass dried on air
(DOP) and by (b) ethanol exchange (EOP), (c) aqueous
ethanol-soluble material after dialysis (EsOPD), (d)
wis-fraction of EsOPD and (e) ws-fraction of EsOPD;
(
) amide II band; AG – typical spectral pattern of
arabinogalactan.
that EsOPD comprised fragments formed through
metabolic pathways from various pectic polysaccha-
ride components (homogalacturonan, rhamnogalac-
turonan RG-I, xylogalacturonan, arabinan, galactan,
and arabinogalactan) and glycoproteins rich in ara-
binose and mannose (Fu et al., 2007). These were
present in the water phase of the grated pumpkin
biomass comprising up to 95 % of the fresh pump-
kin tissues (Mc Cance & Widdowson, 1991) and they
were not precipitated by an addition of ethanol during
the solvent-exchange drying process.
FTIR spectrum of the ws-EsOPD fraction (Fig. 2)
confirmed this suggestion showing absorption bands
of carboxylate (1604 cm
−1
) and ester (1740 cm
−1
)
groups and bands in the mid-infrared region typical
of pectic arabinogalactans at 1074 cm
−1
, 1045 cm
−1
,
and 864 cm
−1
(Kačuráková et al., 2000). The small ab-
sorption band at 1510 cm
−1
in the spectrum of EOP
is related to aromatic ring vibrations, confirming the
presence of lignin and other phenolics. The band at
1546 cm
−1
corresponds to N—H deformation (amide
II) vibration of protein and/or polyamine (amide I vi-
bration of protein might be overlapped by the car-
bonyl stretching) and those at 2958–2854 cm
−1
to
methyl and methylene stretching vibrations of lipids,
respectively. As can be seen, proteins and lipids are
accumulated in the insoluble fraction (wis-EsOPD).
This is in accordance with the, only slightly, increased
level of extractives in EOP in comparison to DOP (Ta-
ble 1), caused by partial removal of extractives during
the ethanol-drying treatment. In accordance with the
aim of this study, drying by solvent exchange has the
advantage of alcohol-insoluble residue (EOP) contain-
ing the bulk cell wall polymers, which is of importance
for the characterization of non-cellulosic polysaccha-
ride components of the oil pumpkin biomass.
Fractional extraction of seeded oil pumpkin
fruit biomass (EOP)
In order to isolate easily extractable non-cellulosic
polysaccharides, EOP was subjected to a simple two-
step extraction procedure using water in the first and
1 % NaOH at elevated temperature in the second step
(Fig. 1). The yield and analytical data of the released
cell wall polysaccharide fractions EOP-W and EOP-
A, respectively, and of the extraction residue (EOP-
R)aresummarizedinTable2. Extracted polysaccha-
rides contained about 2–3 % of total phenolics (TP),
however, no Klason lignin was determined. This lignin
(20.9 %) remained in the extraction residue EOP-R.
The sugar composition of both fractions unequivocally
indicated the prevalence of pectic polymers with a
high proportion of arabinose and galactose represent-
ing neutral side chains in both fractions. These agrees
with the results of Ptitchkina et al. (1994), who found
a high level of neutral sugar side chains in pumpkin
pectin. Xylose-containing hemicelluloses (xyloglucan
and xylan) were released in somewhat higher amounts
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410 Z. Košťálová et al./Chemical Papers 63 (4) 406–413 (2009)
Tabl e 2 . Yield and analytical data of non-cellulosic water-extractable (EOP-W) and alkali-extractable (EOP-A) polysaccharide
fractions of oil pumpkin biomass (EOP) and its extraction residue (EOP-R)
w
i
/% Neutral sugars, x
r
/mole %
Sample
Yield
a
N
b
TP
b
UA
b
Rha Fuc Ara Xyl Man Glc Gal
EOP-W 2.1 2.5 2.1 27.9 3 2 34 11 6 11 33
EOP-A 12.9 3.5 3.3 36.1 5 2 41 18 0 13 20
EOP-R 53.2 nd 20.9
c
nd 0 0 0 3 5 88 4
Analytical data are means of at least two experiments. a) Related to oven-dried EOP; b) calculated on air-dry basis; c) phenolics
determined as Klason lignin. TP – total phenolics content, nd – not determined. See footnote in Table 1.
Tabl e 3 . Analytical data of peel (P), flesh (F), and hair-like flesh (HF) of standard pumpkin (SP) and oil pumpkin (OP) biomasses
Content, w
i
/%
a
Neutral sugars, x
r
/mole %
Sample
Ash ES TC
b
UA Rha Fuc Ara Xyl Man Glc Gal
SP/P 8.4 20.2 7.8 33.8 2.8 1.6 26.2 8.8 7.7 33.0 19.9
SP/F 5.5 20.7 4.6 62.4 1.6 0.7 9.2 7.3 6.5 58.1 16.6
SP/HF 9.0 23.8 7.9 45.8 4.5 1.0 9.1 12.3 5.4 53.5 14.2
OP/P 11.0 20.1 9.2 31.8 10.0 Tr 13.4 13.0 8.1 43.9 11.6
OP/F 6.6 18.9 4.7 67.7 1.9 0.9 4.3 5.8 10.3 68.0 8.8
OP/HF 10.0 21.8 6.0 50.2 4.2 1.7 13.3 17.5 6.4 39.4 17.5
Values are means of at least two experiments. a) Calculated on oven-dry basis; b) determined by the modified phenol–sulfuric acid
assay. See footnote in Table 1.
Fig. 3. FTIR spectra of (a) water-extracted (EOP-W) and (b)
alkali-extracted (EOP-A) polysaccharides of oil pump-
kin biomass, (c) citrus pectate, and (d) 20 % methyl
esterified citrus pectin; (
) amide II band; P – typical
pectin bands.
in the alkaline step. Fucose is indicative of xyloglu-
can which is the predominating hemicellulose compo-
nent in pumpkin primary cell walls (Ratnayake et al.,
1999).
FTIR spectra of the EOP-W and EOP-A frac-
tions (Fig. 3) confirmed the prevalence of pectin by
intense bands at 1144 cm
−1
, 1100 cm
−1
, 1070 cm
−1
,
1047 cm
−1
, 1017 cm
−1
, and 956 cm
−1
(Kačuráková
et al., 2000). Supported by the spectral pattern of
standards (methyl esterified pectin and pectate), data
in Fig. 3 indicate that the pectin polysaccharides in
EOP-W are partially methylated (νC
—
—
Oesterat
1740 cm
−1
), while those in the EOP-A fraction ap-
pear to be in the carboxylate form (ν
as
COO
−
at
1604 cm
−1
). The typical bands of xylan (1043 cm
−1
,
1082 cm
−1
, 1162 cm
−1
), xyloglucan (1153 cm
−1
, 1118
cm
−1
, 1078 cm
−1
, 1041 cm
−1
), and arabinogalactan
(1139 cm
−1
, 1074 cm
−1
, 1045 cm
−1
) (Kačuráková et
al., 1999, Kačuráková et al., 2000) are overlapped by
pectin bands. Sugar composition of EOP-R with pre-
vailing glucose and high lignin content corresponds to
the crude lignin-containing cellulose.
Composition of the main pumpkin tissues
In the further part of the study, the fresh seeded
fruit biomasses of SP and OP were separated into
three tissues – peel (P), flesh (F), and inner hair-like
flesh (HF), with the aim to characterize their contri-
bution to the composition of the whole biomass. The
separated tissues were dried by the ethanol method
described above for OP and were, therefore, accom-
panied by the mass loss caused by dissolution and
decantation of low-molar mass, ethanol-soluble com-
pounds.
Relative proportions of the isolated tissues and
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Tabl e 4 . Comparison of SP and OP composition data derived from the proportions and compositions of the P, F, and HF tissues
Content, w
i
/%
Sample
AshLigninPectin
a
NC
b
α-Cellulose
SP 6.4 4.0 20.9 34.1 27.4
OP 7.9 7.6 19.3 38.1 29.2
Composition data (in % on oven-dry basis) are calculated from analysis data of the P, F, and HF tissues (Table 3); a) expressed
as uronic acid content; b) neutral carbohydrates (NC) content was calculated as a difference between total carbohydrates content
and the content of pectin.
Fig. 4. Content (% of oven-dried sample) of lignin (full)
and polysaccharide components – pectin, expressed as
uronic acids content (dotted), neutral carbohydrates
(empty), and α-cellulose (dashed) in the peel (P), flesh
(F), and hair-like flesh (HF) of standard pumpkin (SP)
and oil pumpkin (OP). The relative proportions of the
tissues are expressed in percentage.
their main components are illustrated in Fig. 4 and
summarized in Table 3. In comparison to SP, OP
showed a higher proportion of P (27 % vs. 20 %),
about the same proportion of F (69 % vs. 70 %) and
a lower proportion of HF (4 % vs. 10 %). As shown in
Fig. 4, the distribution patterns of lignin, pectin (as
UA content), and α-cellulose components, when com-
paring the corresponding P, F, and HF tissues of OP
and SP, are very similar, but there are differences in
the content of the components.
Differences in the lignin content between SP and
OP were observed in all tissues. The peel of both, SP
and OP, was rich in lignin; its content was by about
60%higherinOPthaninSP.Thefleshcontainedlow
amounts of lignin, but its amount in OP was twice that
in SP. On the contrary, HF of the oil cultivar (mutant)
showed a very low content of lignin (2.2 % vs. 5.3 %
in SP) and a higher content of extractives (7.9 % vs.
6.0 % in SP, Table 3). The differences observed in
the lignin content between HF of SP and OP are in
correlation with the lignin content reported for the
seed coat (testa) of standard pumpkin and its hull-
less mutant (Stuart & Loy, 1983; Bezold et al., 2003),
which was lower in the seed coat of the mutant.
In case of peel tissues from OP and SP, there is
a discrepancy between the contents of neutral carbo-
hydrates and α-cellulose. This can be explained by
the different analytical methods used. Determination
of the total carbohydrate content by colorimetry is
strongly affected by the presence of phenolics, pro-
teins, etc., which might contribute to the color change
in the phenol–sulfuric acid test (Wang et al., 2008).
However, during the analysis of α-cellulose, these com-
ponents were removed from the fiber residue.
The flesh of OP and SP represents 69–70 % of their
biomass. For this tissue, OP and SP showed a similar
pectin content (18.9 % and 20.7 %), but the amount
of neutral carbohydrates and their sugar composition
in OP (Table 3) indicated a higher content of hemi-
cellulosic polysaccharides. However, the pectin compo-
nent had a lower degree of branching by arabinose and
galactose-containing polysaccharides. The higher pro-
portion of non-cellulosic polysaccharides in the flesh
of OP is evident from larger differences between the
neutral carbohydrates content (NC) and α-cellulose.
In addition, the HF of OP showed a greater difference
between the neutral polysaccharides and the pectin
contents in comparison to those of SP.
The most distinct differences were observed with
the HF fractions of OP and SP not only considering
the lignin but also the polysaccharide components. In
comparison to OP, SP showed higher content of glu-
cose and uronic acid. The content of hemicelluloses,
estimated as the sum of xylose and manose, was higher
in OP. It can be presumed that the mutation process
affected not only the composition of seed coat (Stu-
art & Loy, 1983; Bezold et al., 2003) but also of the
endocarp flesh tissue, where the seeds are located.
In comparison with SP, larger amounts of extrac-
tives were present in the peel of OP (Table 3). How-
ever, their amount was considerably lower in the HF
tissue of the hull-less mutant (OP), showing a similar
relation as that of the above mentioned lignin content.
Based on the total carbohydrate content and the
sugar composition (Table 3), the distribution of non-
cellulose cell wall polysaccharides of the P, F, and HF
tissues was very roughly estimated. The uronic acids
content, attributed to pectin, varied from 20.2 % to
23.8 % and 18.9 % to 21.8 % of the SP and OP tissues,
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412 Z. Košťálová et al./Chemical Papers 63 (4) 406–413 (2009)
respectively, and was the highest in the HF tissues.
Due to low proportion of HF in both OP and SP cul-
tivars (4 % and 10 %, respectively); it has no marked
effect on the composition of the whole biomasses.
From the differences between the contents of total
carbohydrates and uronic acids (Fig. 4), higher pro-
portions of neutral polysaccharides belonging to pec-
tic polysaccharides and hemicelluloses were observed
with the OP tissues, varying from 11.7 % to 48.8 %,
whereas the contents varied from 13.6 % to 41.7 %
in the SP tissues. In contrast, the proportions of α-
cellulose in OP and SP tissues were similar (18.8–
32.4 %) and (14.4–31.4 %), respectively. In addition,
the sugar analysis data (Fig. 4, Table 3) indicated a
higher proportion of hemicellulosic polymers in the
OP tissues.
Based on the analytical data of the P, F and HF
tissues in Fig. 4, the proximate content of the main
components of both SP and OP biomasses was calcu-
lated and illustrated in Table 4. When compared to
the SP biomass, OP displayed a much higher content
of lignin, similar content of pectin and a larger propor-
tion of hemicelluloses, whereas the α-cellulose content
was slightly higher.
Conclusion
The presented results suggest that the oil pumpkin
biomass represents a potential source of non-cellulosic
polysaccharides (hemicelluloses and pectic polysac-
charides). Although the content of pectin is some-
what lower in OP, the advantage of this polysac-
charide component is in its low degree of branching
by arabinose- and galactose-containing polysaccharide
side chains. This is of particular importance for the po-
tential production of pectin for the food industry. Non-
cellulosic polysaccharides are associated with pheno-
lics and other extractive compounds. Such phenolics-
rich polysaccharides might exert antioxidant activities
which have been reported for preparations obtained
from other plant sources, such as wheat bran (Yuan
et al., 2005), spruce wood (Ebringerová et al., 2008a),
and almond shells (Ebringerová et al., 2008b). How-
ever, diversity of the hemicellulose and pectic com-
ponents of the oil pumpkin biomass and their asso-
ciation with phenolics needs further investigations in
order to develop possible isolation and potential ap-
plications for these polysaccharides. Currently, inves-
tigations dealing with the selection and optimization
of convenient extraction methods are in progress.
Acknowledgements. This work was financially supported by
the Slovak Grant Agency VEGA, grant No. 2/0062/09 and by
the EEA grant No. SAV-FM-EHP-2008-03-05. The authors are
grateful to Dr. V. Sasinková for the FTIR measurements.
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