1. Introduction

Cork, the outside part of the oak (Quercus suber L.), is a natural, renewable, sustainable raw material, which is periodically harvested from the tree, usually every 9–12 years, depending on the cultivation region [1]. Quercus suber L. is a tree that grows slowly in same regions of the western Mediterranean (Portugal, Spain, Southern France, part of Italy and North Africa) and China [2–4]. Portugal is the main cork producer, transforming about 75% of all the cork [3, 4]. Industrial transformation of cork generates up to 25 wt.% of cork dusts as by-product [5, 6].

Cork wastes and cork powders have been used as bioadsorbents for removing pesticides and other pollutants from wastewaters with promising results [7].

Biosorption is an emergent technology expected to show strong growth soon because it offers high cost effectiveness, although further improvements in its performance are needed [1]. Environmental protection legislation is becoming progressively important and effective solutions will be at premium [8].

The cork material is compact, devoid of intercellular spaces and with a regular honeycomb organisation (Figure 1). This material is composed by dead parenchymatous cells with voids, prismatic, air-filled interiors, hexagonal on average and are arranged base-to-base in an alignment oriented in the tree's radial direction [9].

adsorption capacity increasing with the increase in concentration of these wine

Air Depleted and Solvent Impregnated Cork Powder as a New Natural and Sustainable Wine…

and growth of Dekkera/Brettanomyces yeasts result in the formation of 4-EP and 4-EG by decarboxylation of p-coumaric and ferulic acids present in wine and subsequent reduction of the correspondent vinylphenols (Figure 2) [11, 12].

and thus, VPs are a generalised problem in red winemaking.

VPs chitosans has been shown to be effective [24].

2. Cork chemical composition

Adapted from [1, 25, 34–36].

Chemical composition of cork.

Table 1.

231

In red winemaking, especially those aged in wood barrels, the contamination

These VPs are responsible for negative aromatic notes like horsy sweat, smoky, barnyard and medicinal [11, 13]. This important sensory defect has been reported in several wine styles around the world, especially, premium wines [14, 15], considered negative by professionals, consumers and wine industry [16, 17],

For these reasons, several treatments to avoid or to reduce compounds have been tested. Preventive action includes, for example, the maintenance of adequate levels of sulphur dioxide throughout the winemaking process, reduction/elimination of oxygen levels in wine, use of dimethyl dicarbonate (DMDC) before bottling and the addition of fungal chitosan, which are some of the measures that have found some degree of success [18, 19]. Several remediation treatments have also been developed to eliminate the already formed VPs from wine or to decrease the headspace content by decreasing their partition coefficients to the gas phase without changing the total wine VP content. Of these methods, those tested in wines presenting good removal efficiency at practical application doses are activated carbons [20, 21], potassium caseinate [22], egg albumin [22] and esterified cellulose [23]. Nevertheless, although they are efficient in reducing the total amount of VPs in wines, the use of potassium caseinate and egg albumin presented the risk of the potential allergenicity of these fining agents and therefore it is mandatory to label the wine bottle if the residual concentration is higher than 0.25 mg/L (EU Regulation 579/2012). For the decrease of headspace abundance of

The success of cork powder in adsorption of VPs from such a complex matrix

as wine without affecting the wine quality significantly in terms of phenolic composition is certainly due to the structure and chemical composition of its main

The chemical composition of cork has been widely examined [25–33] and presented some variability that depends on factors such as geographic origin, soil

Principal components (%) Range Average Suberin 40–53 45.8 Lignin 21–29 24.4 Polysaccharides 10–16 12.5 Extractives 6–19 12.6 Tannins 6–7 6.5 Ash 0.85–2.1 1.4

components namely suberin, lignin and cell wall polysaccharides.

contaminants [10].

DOI: http://dx.doi.org/10.5772/intechopen.85691

The cells are small and have sizes under those of synthetic foams. The area of the prism base is 4–<sup>6</sup> <sup>10</sup><sup>6</sup> cm with a mean prism edge of 13–<sup>15</sup> <sup>μ</sup>m; prim height is usually in the range of 30–40 μm. The mean cell volume is approximately <sup>2</sup> <sup>10</sup><sup>8</sup> cm3 and the number of cells per unit is 4–<sup>7</sup> <sup>10</sup><sup>7</sup> cm<sup>3</sup> . The cell walls are thin with a thickness of 1–1.5 μm. The solid mass volume fraction of the cork is only about 10%.

Cork powder maintains the cork cellular structure intact [10], and its adsorption properties can be improved by removing the air and simultaneous impregnation with ethanol rendering the cell wall components more accessible to the adsorbates [10]. This simple treatment was shown to increase cork powder adsorption capacity of 4-EP and 4-EG by at least 4 times in a real wine matrix, with the cork powder

#### Figure 1.

Structure of cork as observed by SEM in the two main sections: (A) tangential section, perpendicular to the tree's radial direction; (B) transverse section, perpendicular to the tree's axial direction.

#### Figure 2.

Formation of volatile phenols from hydroxycinnamate precursors or their degradation products (vinylphenols) in wines by Dekkera/Brettanomyces.

Air Depleted and Solvent Impregnated Cork Powder as a New Natural and Sustainable Wine… DOI: http://dx.doi.org/10.5772/intechopen.85691

adsorption capacity increasing with the increase in concentration of these wine contaminants [10].

In red winemaking, especially those aged in wood barrels, the contamination and growth of Dekkera/Brettanomyces yeasts result in the formation of 4-EP and 4-EG by decarboxylation of p-coumaric and ferulic acids present in wine and subsequent reduction of the correspondent vinylphenols (Figure 2) [11, 12].

These VPs are responsible for negative aromatic notes like horsy sweat, smoky, barnyard and medicinal [11, 13]. This important sensory defect has been reported in several wine styles around the world, especially, premium wines [14, 15], considered negative by professionals, consumers and wine industry [16, 17], and thus, VPs are a generalised problem in red winemaking.

For these reasons, several treatments to avoid or to reduce compounds have been tested. Preventive action includes, for example, the maintenance of adequate levels of sulphur dioxide throughout the winemaking process, reduction/elimination of oxygen levels in wine, use of dimethyl dicarbonate (DMDC) before bottling and the addition of fungal chitosan, which are some of the measures that have found some degree of success [18, 19]. Several remediation treatments have also been developed to eliminate the already formed VPs from wine or to decrease the headspace content by decreasing their partition coefficients to the gas phase without changing the total wine VP content. Of these methods, those tested in wines presenting good removal efficiency at practical application doses are activated carbons [20, 21], potassium caseinate [22], egg albumin [22] and esterified cellulose [23]. Nevertheless, although they are efficient in reducing the total amount of VPs in wines, the use of potassium caseinate and egg albumin presented the risk of the potential allergenicity of these fining agents and therefore it is mandatory to label the wine bottle if the residual concentration is higher than 0.25 mg/L (EU Regulation 579/2012). For the decrease of headspace abundance of VPs chitosans has been shown to be effective [24].

The success of cork powder in adsorption of VPs from such a complex matrix as wine without affecting the wine quality significantly in terms of phenolic composition is certainly due to the structure and chemical composition of its main components namely suberin, lignin and cell wall polysaccharides.

### 2. Cork chemical composition

The chemical composition of cork has been widely examined [25–33] and presented some variability that depends on factors such as geographic origin, soil


Biosorption is an emergent technology expected to show strong growth soon because it offers high cost effectiveness, although further improvements in its performance are needed [1]. Environmental protection legislation is becoming progressively important and effective solutions will be at premium [8].

Advances in Grape and Wine Biotechnology

<sup>2</sup> <sup>10</sup><sup>8</sup> cm3 and the number of cells per unit is 4–<sup>7</sup> <sup>10</sup><sup>7</sup> cm<sup>3</sup>

about 10%.

Figure 1.

Figure 2.

230

in wines by Dekkera/Brettanomyces.

The cork material is compact, devoid of intercellular spaces and with a regular honeycomb organisation (Figure 1). This material is composed by dead parenchymatous cells with voids, prismatic, air-filled interiors, hexagonal on average and are arranged base-to-base in an alignment oriented in the tree's radial direction [9]. The cells are small and have sizes under those of synthetic foams. The area of the prism base is 4–<sup>6</sup> <sup>10</sup><sup>6</sup> cm with a mean prism edge of 13–<sup>15</sup> <sup>μ</sup>m; prim height is usually in the range of 30–40 μm. The mean cell volume is approximately

thin with a thickness of 1–1.5 μm. The solid mass volume fraction of the cork is only

Structure of cork as observed by SEM in the two main sections: (A) tangential section, perpendicular to the tree's

Formation of volatile phenols from hydroxycinnamate precursors or their degradation products (vinylphenols)

radial direction; (B) transverse section, perpendicular to the tree's axial direction.

Cork powder maintains the cork cellular structure intact [10], and its adsorption properties can be improved by removing the air and simultaneous impregnation with ethanol rendering the cell wall components more accessible to the adsorbates [10]. This simple treatment was shown to increase cork powder adsorption capacity of 4-EP and 4-EG by at least 4 times in a real wine matrix, with the cork powder

. The cell walls are

and climate conditions, genetic origin, tree dimensions, age and growth conditions (Table 1). Cork from Quercus suber L. has specific properties such as low permeability and great elasticity; this is the result, at least partially, from its specific chemical composition (and more especially from that of suberin) [26, 29, 31–33]. The cork cell wall structure consists in a thin internal primary cork cell wall rich in lignin and a thick secondary wall rich in suberin, alternating with a wax lamella and a thin tertiary wall of polysaccharides.
