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