2.1 Suberin

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

2.2 Lignin

Figure 4.

α-O-4<sup>0</sup>

233

, β-β´, β-5<sup>0</sup>

2.3 Polysaccharides

, 5-5<sup>0</sup>

, 4-O-5<sup>0</sup> or β-1<sup>0</sup>

removed from cell walls, a total collapse of the cells is observed.

Schematic representation of lignin structure (adapted from Achyuthan et al. [39]).

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>

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

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

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

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-methylglucurono-

arabinogalactoglucoxylan [41–44]. Xylans in the cell walls are amorphous and the

. The specific relation of the monomers and

,

Figure 3. Schematic representation of suberin structure (adapted from Graça [37]).

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

Figure 4. Schematic representation of lignin structure (adapted from Achyuthan et al. [39]).
