## 3 Results and Discussion
Regarding ketones, SS1 corks with a higher 2-heptanone content stood out, although no significant differences were found with the SS2 corks, which were also from southern Spain. Among the benzene compounds identified, several alcohols, aldehydes, ketones, and esters were detected. The P1 samples from Portugal were distinguished by their elevated concentration of total benzene compounds, primarily because of their greater content of dimethyl benzene, benzaldehyde, benzyl alcohol and phenylethanol. However, no significant differences were observed among the cork samples from Spain. Benzaldehyde, known for its bitter almond-like odor, was prominent in all the samples, particularly in the P1 corks. Benzaldehyde in corks can originate from different sources, including the natural degradation of lignin and the use of certain processing techniques during cork manufacturing. The presence of benzaldehyde in corks has been studied, and its impact on the sensory properties of wine has been evaluated [14; 16]. On the other hand, vanillin and guaiocal, both identified in all natural cork samples, are well-known compounds associated with the aroma of vanilla and spices found in winesaged in oak barrels [32]. Both compounds originate from the natural degradation of lignin, which occurs during the production of barrels through the storage and heating of oak wood [33]. The presence of these compounds in cork may increase during the processing of cork planks and stoppers. In addition, higher concentrations of these compounds have been found in corks contaminated by microorganisms capable of attacking lignin, similar to benzaldehyde and benzyl alcohol [21]. The transfer of these compounds to hydroalcoholic solutions, such as wine, has also been demonstrated [11; 34], so their presence in corks must be considered, particularly in the case of guaiacol, which is associated with the musty aroma of \"cork taint\" [34]. In addition to their high content of benzene compounds, the P1 cork samples from Portugal also showed higher levels of esters and total alcohols. Among the esters, three medium-chain fatty acid ethyl esters, ethyl hexanoate, ethyl octanoate, and ethyl decanoate, were particularly prominent. These compounds are known for their fruity notes in young white wines [35]. Previous studies have identified ethyl hexanoate in corks [13], and research has shown that other ethyl esters and acetates, such as ethyl butyrate or butyl acetate, can migrate from cork to wine solutions, potentially enhancing wine aroma [11]. Therefore, the presence of these esters in corks could have a positive impact on wine quality. Regarding alcohols, the P1 corks stood out for their significant content of 2-ethyl-1-hexanol, which differentiated them from the other samples in terms of alcohol composition. Although this compound is naturally present in various plants and has been identified in corks from different geographical origins in previous studies [12; 16; 21], its widespread use as a fragrance ingredient in plastics and pesticides raises concerns about possible contamination in cork production [36]. Finally, the analysis revealed the presence of five furanic and pyranic compounds, with furfural being the major compound, especially in the Spanish samples, followed by 2-pentylfuran, 5-methylfurfural, 1H-pyrrole-2-carboxaldehyde, and 2,3-dimethylpyrazine. These compounds, known for their toasty aroma, are typically produced by the thermal degradation of polysaccharides and are commonly found in woods of the Quercus genus [33]. However, cork sanitization processes that use high temperatures can also increase the levels of these compounds. [PERSON] et al. [37] described the influence of the heat treatment of corks on their content of furfuraldehydes. More recently, [PERSON] et al. [38] observed an increase in the content of furfural and 5-methylfurfural in heat-treated corks and related these compounds with their sweet aromatic notes. The second major compound, 2-pentylfuran, is a lipid oxidation product of linoleic acid [39].