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CHEMICAL CHARACTERIZATION OF GRAPE STALKS FROM RED GRAPE POMACES
SÓNIA O. PROZIL§ ‡, JOANA A. MENDES§ ‡, DMITRY V. EVTUGUIN§, LUÍS T. DE LEMOS‡, LUÍSA P. LOPES‡
§CICECO and Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal ‡ CI&DETS and Department of Environment, Polytechnic Institute of Viseu, 3504-510 Viseu, Portugal
1. Introduction
The vineyard culture is spread out through all Continents, in which the European Union (EU)
represents 60% of the world production of wine. Portugal, with an annual production of about 7
million hL, is tenth in the world ranking and fifth at the European level (Figure 1) [1]. From the
winemaking process comes the wine, as well as its different by-products (grape skins, grape
stalks, grape seeds, lees and tartar). Among by-products of wine production 100 litters of wine
originates 25 to 31 kg of by-products, depending if we're talking about red or white wine making;
and 1 hL of wine generates 3 to 4 Kg of grape stalks. Regarding the average annual production of
wine, Portugal produces around 24 500 tons of grape stalks per year [2].
2. Chemical Composition
5572
5023
3638
2500
1351
1083
1052
978
761
745
603
533
435
425
400
0 1000 2000 3000 4000 5000 6000
France
Italy
Spain
USA
Argentina
China
Australia
Germany
South Africa
Portugal
Chile
Romania
Hungary
Greece
Russia
1000 Tons
Figure 1: Main world producers of wine [1].
Parameters Content (%)
Ashes 7.0
Extractives
2.3
1.0
23.7
Proteins 6.1
Tannins 15.9
Klason Lignin 17.4
Cellulose Kürscher and Höffer 30.3
Hemicelluloses 21.0
Acetone
Dichloromethane
Water
Table III: Quantitative estimation of different structural
elements in grape stalks dioxane lignin from 13C NMR
spectrum.
Aiming a better understanding of grape stalks and the evaluation of its potential as a source of
new materials, particularly for the acquiring of cellulosic pulp the general chemical composition
have been evaluated. Table I presents the grape stalk’s chemical composition and Table II the
results of sugar's analysis.
The chemical characterization showed that grape stalks are lignocellulosic materials, in which
cellulose is the major component (with around 30%), followed by insolvent hemicelluloses in
hot water (21%) and lignin (17.4%). Regarding other components, it’s important to highlight
the high presence of tannins (15.9%) and extractatives in water (23.7%). Taking into account
the monosaccharide’s analysis (Table II), it can be verified that, after cellulose, xylans are the
second major polysaccharide component present in grape stalks (with around 12%).
References [1] - Vitivinicultura - Diagnóstico Sectorial, Gabinete de planeamento e políticas, 2007, Ministério da Agricultura e do Desenvolvimento Rural e das
Pescas.
[2] - Costa, M., Aproveitamento de Subprodutos da Vinificação. O Bagaço como Matéria-Prima da Indústria de Óleos e de Fabrico de Rações para
Gado, in 1º Congresso Nacional das Industrias Agro-Alimentares, 1983, Ministério da Agricultura Comércio e Pescas.
[3] - Evtuguin, D.V., et al., Comprehensive Study on the Chemical Structure of Dioxane Lignin from Plantation Eucalyptus globulus Wood. J. Agric.
Food Chem., 2001, 49(9): pp. 4252-4261.
3. Cellulose
4. Lignin
5. Xylans
6. Conclusions
Cellulose, the most abundant polymer of grape stalks, was isolated by the Kürscher and Höffer
method and characterized by X-ray diffraction to acquire information regarding its crystalline
structure. The diffractogram (Figure 2) demonstrates that this cellulose is Cellulose I with
characteristic reflexes at ca. 2θ =16 and 22º. The degree of crystallinaty obtained was of about
75%. The dimensions of the unitary cell (a, b and c) and the γ angle are presented below.
In this work the chemical composition and the structure of main macromolecular components of
grape stalks from red grape pomaces have been evaluated aiming to provide the new
strategies for their processing to value added products.
[ -D-Xylp]-(1g4)- [ -D-Xylp]4-(1g4)- [ -D-Xylp]57 -(1g4)- [ -D-Xylp]19 -(1g4)- [ -D-Xylp]14-(1g4)- [ -D-Xylp]6-(1g
2
1 4-O-Me- -D-GlcpA
3
Ac
3
Ac
2 3 2
Ac Ac Ac
Lignin was isolated by acidolysis using a solution
of dioxane-water (9:1 v/v) under acidic conditions
[3]. The nuclear magnetic resonance spectroscopy
is a technique used for the characterization,
classification and structure determination of
lignins. Figure 3 presents the HSQC spectrum of
dioxane lignin, which shows the predominance of
β-O-4, β-5, β-β and β-1 linkages in lignin’s
structure. The 13C NMR analysis allowed the
estimation of the amounts of particular structures.
Table III presents different structural elements in
grape stalks dioxane lignin as reveaved from
13CNMR spectrum.
Monosaccharide’s %(wmon/ wt mon)
Rhamnose 1.7
Fucose <0.2
Arabinose 5.5
Xylose 20.4
Mannose 4.8
Galactose 4.9
Glucose 62.7
Structural element Number / aromatic
group C6
β-O-4 0.36
β-β + β-5 0.08
Ar-O 2.07
Ar-C 1.66
Ar-H 2.27
G:S 73:27
Unit Cell Dimensions
a – 8.0 nm
b – 1.03 nm
c – 7.9 nm
γ - 91º
Table II: Neutral sugars in grape stalks.
Table I: Chemical composition of grape stalks (% dry material).
Figure 3: Aliphatic side-chain region of HSQC spectrum
of grape stalks dioxane lignin.
Ackowledgment Sónia Prozil wish to thank to TAVFER group for supplying the grape stalks samples and for the financial support.
The xylans were extracted with DMSO from the holocelluloses obtained by delignification of grape
stalks with peracetic acid. The DMSO-extracted xylan was characterized by 1D and 2D NMR, which
allowed the proposition of an empiric structure of the grape stalks O-acetyl-(4-O-methyl- -D-
glucurono)xylan as presented below:
The β-O-4 structures are the most
predominant, representing about 36% of the
linkages, followed by the β-β e β-5 structures
with about 8%. It was not possible to quantify
the β-1structure by 13C NMR, but its presence
was confirmed by HSQC. Lignin was also
characterized by nitrobenzene oxidation, from
which the ratio between the main structural
units (H:G:S) was estimated. The found ratio
was of 7:71:26, concordant with the results
obtained by 13C NMR (Table III).
This work allowed a deeper knowledge regarding the chemical composition of grape stalks to
evaluate its potentialities towards cellulosic pulp and biocomposites production. The cellulose
content in grape stalks was relatively low though unusually high degree of its crystallinity was
detected. The heteroxylan was the second in abundance after cellulose polysaccharide in grape
stalks possessing a low degree of the ramification with uronic moieties. The grape stalks lignin is a
HGS type lignin with predominance of G units, very condensed and structurally associated to
tannins.
ppm (t2)
3.003.504.004.505.005.506.006.50
50
60
70
80
90
ppm (t1)
Cβ in β-1
Cβ in β-5
Cβ in β-β
Cγ in β-1
Cβ in β-5
Cγ in β-O-4
Sugars
Cγ in β-β
Cα in β-O-4
Cα in β-1 Cα in β-O-4
Cβ in β-5 Cγ in β-β
Ic Ic
Iam
2θ (º)
Inte
ns
ity
Figure 2: X-ray difractogram of cellullose isolated by the Kürscher and Höffer method.