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ADSORPTION PROPERTIES OF CORK MATERIAL FOR WATER VAPOUR
Institut Universitaire de la Vigne et du VinEquipe EMMA- Université de Bourgogne
1 Equipe EMMA, ENSBANA, Université de Bourgogne, F-21000 Dijon2 Institut Universitaire de la Vigne et du Vin, Université de Bourgogne, F-21078 Dijon3 Institut Carnot de Bourgogne, UMR 5209, CNRS-Université de Bourgogne, F-21078 Dijon
Sonia Lequin1,2,3, Jean-Pierre Bellat3, Thomas Karbowiak1, Régis Gougeon1,2, Laurent Brachais1, David Chassagne1,2
Euro Food Water6th Conference on water in food
21-23 March 2010Maison des Agriculteurs, Reims
Field research: white wine oxidation
Introduction
Oxidation leading to sensory defaults and consumer refusing
Polyphenols
O2
Question:What is the impact of the natural cork stopper on the wine oxidation?
Introduction
CH2OWater(≈88%)
PH2O
In case of upright position storage the head space between wine and cork stopper is saturated with water vapour
Water effect on cork structure?Water as solvent of wine molecules (SO2, O2)
Objective
To perform a thermodynamic study of water vapour on cork in order to better understand the interactions of water with cork.
Material and methods
Cork material
Virgin natural cork (Quercus Suber L.) from the bark of oak trees (Portugal).Physical characterisation:
80 µm
Materials and methods
Cork materialMechanical properties:- Elasticity- Compressibility
Chemical composition:
Suberin: ≈ 50% lignin: ≈ 30% polysaccharides: ≈ 10-20%extractibles: ≈ 10-20% ashes: ≈ 1-5% others: ≈ 1-5%
The structure of suberin (Cordeiro et al., 1998)
Materials and methods
Thermogravimetry
Pressure captor
Adsorbat
Oven at 25°C
Piece of corkw = 40 mg
Water: 10-5 < P < 31 hPa
35 m
m
R
T
A
10 mm1 mm
R-T A-R
A-T
Lens
Mirror
Photoelectric cell
Light
P
Vacuum10-5 hPa
Materials and methods
Differential calorimetry in isothermal condition, coupled with manometry
Heat released during gas adsorption process on cork powder w = 600 mg
water
Water: 10-5 < P < 31 hPa
Adsorption isotherm at 25°C
0
1
2
3
4
5
6
0 0.2 0.4 0.6 0.8 1
adsorptiondesorption
P/Ps
Amount of water adsorbed
(mmol.g-1 dry cork)Type II isotherm: non porous or macroporous solid (IUPAC).
weak slope: low affinity
Maximum water adsorbed amount: ≈ 6 mmol.g-1 as 10%
Low hysteresis during desorption: irreversible process, structural change (swelling)
Total water desorption under vacuum: physisorption phenomenon, weak bonds
Adsorption isotherm at 25°C
0
1
2
3
4
5
6
0 0.2 0.4 0.6 0.8 1p/ps
Amount of water adsorbed
(mmol.g-1 dry cork)
BET
GAB
Best fit with the GAB model
adsorption process by clustersformation around localized adsorption sites
Adsorption heat released during adsorption on cork at 25°C
Exothermic phenomenon
Low heat of adsorption: ≈ 60 kJ·mol-1
0
20
40
60
80
100
0 1 2 3
ΔHL = - 44 kJ.mol-1
Amount of water adsorbed
(mmol.g-1 dry cork)
Adsorption enthalpy
IΔHaI kJ.mol-1
Physisorption
NMR
74.6
Cork (RH=11%)Cork (RH=98%)
δ (ppm)
173.
0
130.
1
105.
1
82.4
72.3
64.4
56.2
32.9
30.1
21.3
-40-20020406080100120140160180200
-COO--CH-
(C1-suberin) -CH-(C4-suberin)
-CHOH-C 2,3,5
-(CH2)n-
-OCH3C6CH3-COO-
-CH=CH-
Water is mainly adsorbed on hydrophilic sites constituted by hydroxyl and methoxyl groups.
Cork (p/ps=0.11)Cork (p/ps=0.98)
Conclusion and perspectives
Adsorption mechanism of water vapour on cork is in two steps. (i) First, water adsorbs on hydrophilic sites constituted by hydroxyl and methoxyl groups. (ii) Then water adsorption continues by clusters formation around the hydrophilic sites.
Thermodynamic study of gaseous ethanolCo-adsorption studies of:
- water / SO2- water / O2
Gas (oxygene, SO2) permeability studies of cork will be lead through the cork
O2, SO2
Institut Universitaire de la Vigne et du VinEquipe EMMA- Université de Bourgogne
Thank you for your attention