## 4 Bioactive Compounds on Cork and Cork By-Products  
The composition of cork includes a variety of compounds from different chemical families, namely terpen, sterols, saccharides, suberin, lignin, and other phenolic compounds, whose concentrations are dependent on several factors, such as climate, region, age, or the part of the tree [23; 52]. Cork extractives are constituted by compounds with low molecular weight that are not connected to structural elements [33]. Aliphatic extractives, also known as waves, are originated using nonpolar solvents, such as hexane or dichloromethane, while phenolic extractives are obtained from polar solvents, such as water or ethanol [53]. Suberin is the major component found on cork cell walls (30-50%), responsible for the low permeability and elasticity of this material, working as a protective barrier from the environment [54]. Cork suberin is a lipophilic polyester macromolecule, where monomers, such as long-chain fatty components, glycerol, hydroxyfatty, and phenolic acids are connected by ester groups [54; 55; 56]. The analysis of its monomeric fractions is possible thanks to depolymerization methods, concluding that suberin is constituted by an aromatic and an aliphatic domain. Among them, long-chain \(\omega\)-hydroxyfatty acids and \(\alpha\),\(\omega\)-dicarboxylicacids are the main aliphatic components, while ferulic acid is the principal aromatic component [57]. Despite being normally discarded due to its poor quality, virgin cork usually has more superin than reproduction cork. In addition, cork powder is another rich source of suberin that can be valued in new applications [58]. For example, the aliphatic components from suberin are scarce in nature and can favour their industrial interest for the synthesis of polymeric materials [56; 59]. Suberin extracts also showed antimutagenic properties and skin-firming properties [36] and acted in a desmutagenic manner [60]. Lignin is another hydrophobic polymer present on cork which works as the mechanical support of cell walls, believed to be the principal aromatic fraction of cork [61; 62]. Studies indicate that lignin appears in the three layers from cork cell walls, although at different concentrations [63]. Cork powder often contains greater amounts of lignin than the original cork [64]. Additionally, lignin contains UV-absorbing properties which make it interesting to incorporate in sunscreens [65]. The minor components, cellulose and hemicellulose, are hydrophilic polysaccharides that confer structural rigidity to cork cells [66]. Even so, the bark of _Q. suber_ L is essentially composed of the monomeric units of glucose, xylose, and arabinose, contrary to what happens with other species [23]. Waxes include lipophilic, aliphatic, and aromatic compounds that along with suberin contribute to cork impermeability [67]. Triterpenes are the most abundant compounds found on waves in addition to still having n-alkanes, n-alkanols and fatty acids [53]. Cerin (**1**), friedelin (**2**), betulin (**3**), betulinic acid (**4**), and sterols are examples of triterpenes that can be used as bioactive components (Figure 2) [68; 69]. Dichloromethane cork extracts have been found to have a high amount of friedelin (**2**), betulin (**3**), betulinic acid (**4**), and \(\beta\)-amyrin (**5**), as well as sterols, such as sitost-4-en-3-one (**6**) (Figure 2) [28]. However, a higher number of sterols can be obtained using supercritical CO\({}_{2}\) as a solvent. Cork extraction using a dichloromethane/methanol mixture demonstrated that the most abundant triterpenes on cork are cerin (**1**) and friedelin (**2**), while betulinic acid (**4**) and friedelin (**2**) are the main components from cork powder and black condensate, respectively [59; 67]. Figure 2: Chemical structures of bioactive triterpenes found on cork extracts. Phenolic compounds are important secondary metabolites that present a wide range of biological activities [70].