2.2 Lignin

and climate conditions, genetic origin, tree dimensions, age and growth conditions

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

Suberin, a natural aliphatic-aromatic crosslinked polyester, is the major component of cork, accounting for 30–50% of its weight. It is a very important structural component of the cell wall and its removal destroys cell integrity. Suberin polymeric structure is mainly composed by two types of monomers, glycerol and long-chain

(Table 1). Cork from Quercus suber L. has specific properties such as low

fatty acids and alcohols, which are linked by ester bonds, Figure 3 [9].

and a thin tertiary wall of polysaccharides.

Advances in Grape and Wine Biotechnology

2.1 Suberin

Figure 3.

232

Schematic representation of suberin structure (adapted from Graça [37]).

Lignin is the second most important component in cork cell walls accounting for 15–30% of its weight [9]. It is a crosslinked polymer of aromatic nature. Due to the importance of lignin, many studies were done in wood pulping and more recently, for biomass deconstruction [38]. Lignin is a polymer made up by three monomer types of phenyl propane (p-coumaryl, coniferyl and sinapyl alcohols) linked through a free-radical reaction started via enzymatic phenoxy radical formation (Figure 4). The inter-unit linkages in the polymer can be of several kinds: β-O-4<sup>0</sup> , α-O-4<sup>0</sup> , β-β´, β-5<sup>0</sup> , 5-5<sup>0</sup> , 4-O-5<sup>0</sup> or β-1<sup>0</sup> . The specific relation of the monomers and intermonomeric linkages depend on the material [9]. In cork, lignin also contributes to the mechanical support and rigidity of the cell walls. If lignin is selectively removed from cell walls, a total collapse of the cells is observed.

#### 2.3 Polysaccharides

In cork, the cell wall polysaccharides, cellulose and hemicelluloses, represent approximately 20% of its weight. Cellulose is in the primary and tertiary cell walls of cork, accounting for nearly 10% [40]. There is less information concerning the molecular weight, crystallinity and chain orientation of cork cellulose. Cellulose is water insoluble due to an extensive intermolecular hydrogen bonding between adjacent polymers, and interaction with water often only occurs in the amorphous regions. The hemicelluloses are another water insoluble group of polysaccharides present in cork cell walls. The main known hemicellulose polysaccharides comprise three different groups of polysaccharides (Figure 5), the 4-O-methylglucuronoxylan, arabino-4-O-methylglucuronoxylan and 4-O-methylglucuronoarabinogalactoglucoxylan [41–44]. Xylans in the cell walls are amorphous and the

3. Optimised cork powder (CKP) as a wine fining agent to remove

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

The air removal of the cork powder cell structure and simultaneous impregnation with ethanol with or without previous removal of cork extractives increased significantly the 4-ethylphenol and 4-ethylguaiacol adsorption performance (Table 2). Although a significant removal of wine VPs was observed, the overall quality of the treated wine cannot be accessed only by the decrease in these negative aroma compounds, as the impact on the other wine positive aroma components is important to define the final overall sensory olfactory quality [15, 20, 21, 22, 24]. The red wine colour characteristics are important for consumer acceptance of the treated wine, because there is straight relation between the colour and the wine's phenolic composition, namely anthocyanins, whose concentration can be changed by the

In order to have a deeper insight on the impact of optimised cork powder in the wine chemical composition besides the removal efficiency of the VPs, the change in the headspace aroma abundance of wine, phenolic composition and chromatic characteristics were studied and the overall impact on the wine sensory character-

3.1 Impact of optimised cork powder on the wine aroma headspace abundance

Factors Wine spiked levels

A B 4-EP 4-EG 4-EP 4-EG No impregnation CKN 85.3 2.7a 9.2 0.2<sup>a</sup> 109.6 5.1<sup>a</sup> 10.5 0.6a

Vacuum impregnation CKNI 270.9 11.8c 43.4 2.1<sup>c</sup> 888.0 16.3c 133.8 2.0<sup>c</sup>

Values are presented as mean standard deviation; medium spiking levels: 750 μg/L 4-EP and 150 μg/L 4-EG; high 1500 μg/L 4-EP and 300 μg/L 4-EG. Means within a column followed by the same letter are not significantly different

Amount of 4-EP and 4-EG (μg/L) removed from wines at two spiked levels<sup>a</sup> of natural cork powder (CKN) and dichloromethane and ethanol extractive free cork powder (CKF) before and after air removal and

A 0.0000001 0.000011 0.0000001 0.0000001 B 0.0000001 0.0000001 0.0000001 0.0000001 A B 0.0029 0.083033 0.0000001 0.000018

Air removal and ethanol impregnation of cork samples with and without extractive removal decreased the total headspace aroma abundance (CKNI 32% and CKFI 37%) significantly. The decrease in the particle size of the CKF did not differ significantly on the removal of headspace aroma compounds, although there was an average decrease of 3.7% in relation to CKF (Table 3). The duplication in application dose of CKFI75 resulted in a significant decrease of the total abundance of headspace aroma by more 29% (Table 3). There was a significant correlation (r = 0.731, n = 14, p < 0.003) between the headspace aroma abundance and the octanol-water partition coefficient (log P) of the aroma compounds, strongly

Medium High

CKF 168.8 4.2b 19.2 2.7<sup>b</sup> <sup>738</sup> 36.9<sup>b</sup> 71.5 5.4<sup>b</sup>

CKFI 306.0 2.3<sup>d</sup> 60.5 1.6d 1036.5 18.1<sup>d</sup> 149.1 3.3d

negative volatile phenols in contaminated red wine

fining procedure.

a

Table 2.

235

ANOVA and Tukey post-hoc test (p < 0.05).

impregnation with ethanol (CKNI and CKNFI) [10].

istics was evaluated by an expert panel.

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

#### Figure 5. Schematic structures of main cork cell wall polysaccharides: (a) cellulose, (b) 4-O-methylglucuronoxylan, (c) arabino-4-O-methylglucuronoxylan and (d) 4-O-methylglucurono-arabinogalactoglucoxylan.

irregular occurrence of branching of the main chain does not permit strong intermolecular association by hydrogen bonding; nevertheless, they are extracted using strong alkaline solutions (4–10% w/v NaOH). Pectins also exist in low quantities in cork, approximately 1.5%, placed in the middle lamella [45].

#### 2.4 Extractable components

Cork contains 8–20% of low molecular weight compounds including fatty acids, terpenes, long-chain aliphatic compounds and saccharides, collectively known as extractives [34, 46]. Cork contains also about 6% of tannins [36]. The most important of these components are waxes and tannins [31]. Waxes are extracted by low polarity solvents, such as benzene, chloroform, ethyl acetate [47], hexane [36] and ether [26]. The waxes are responsible for the cork impermeability. The waxes extracted were found to consist of two fractions: neutral and acidic. The neutral fraction is mostly composed of fatty alcohols (C18▬C26) with some unsaturated groups and triterpenes.

The acid fraction is essentially composed of fatty acids (C14▬C24) with unsaturated ω-hydroxyacids, 18-hydroxy-9,12-octadienoic and 18-hydroxy-9 octadecenoic acids. More or less 50% of the waxes are triterpenes from friedelin and lupine families including friedelin, 3-α-hydroxyfriedelan-2-one, botulin, betulinic acid, β-sitosterol and sitost-4-en-3-one [48]. Cork extractable phenolic compounds include ellagic acid and some quantities of gallic acid, protocatechuic acid/aldehyde, aesculetin, vanillic acid, caffeic acid, vanillin, scopoletin, ferulic acid, coniferyl aldehyde and sinapaldehyde [49, 50]. The extraction of tannins can be done by polar solvents such as water [51] and ethanol [52]. Cork tannins include roburins A and E, grandini, vescalagin and castalagin. The yields of these two components change in function of the nature of the cork (virgin or reproduction) where significant variation is found in the bibliography [1].

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