## 3 Results and Discussion
### Volatile Compounds
These differences could be motivated by an existence of inequalities in cooking techniques, such as temperatures, times and sample thickness. Like this, [PERSON] et al. [9] used, on grilled samples, higher temperatures (190 vs. 130-150 \({}^{\circ}\)C) and shorter times (4 vs. 10 min) than ours, which can run to less oxidation, so a lower hexanal content. In spite of that, other studies on foal meat [14, 15] found results similar to ours, determining that frying led to lower hexanal values. This incident can be associated with the high content of \(\alpha\)-tocopherol and polyphenols existing in olive oil, which could act to protect against oxidation [71]. In addition, hexanal is supposed to be one of the main indicators of lipid oxidation [79, 81]. For this reason, a good correlation can be expected between TBARS value and this volatile compound. On this matter, we have found that TBARS value were strongly related to hexanal content in both diets, since a positive Pearson correlation was displayed (r = 0.798; \(P<\) 0.01, for chestnut feed pigs; and r = 0.831; \(P<\) 0.01, for commercial feed pigs). Heptanal was another important aldehyde in our research since it could undergo modifications as a consequence of diet. This is because heptanal is a degradation product of oleic acid [51, 75] and the diets rich in this fatty acid (such as chestnut feed) can favour their accumulation in the intramuscular fat of pigs [6, 18] and consequently the heptanal content in cooked samples. However, these differences were not found in the present study. A clear trend was not observed either, since the heptanal content was higher in grilled and fried CH samples, while, for the roasting and microwaving treatments, they were higher in CF samples. Lastly, regarding the \"others\" group, the presence of one ketone should be pointed out, since these compounds are judged to have a high and peculiar influence on meat flavour [79]. The ketone found was the 2-heptanone, which was only significantly affected by diet in the case of frying treatment (\(P<\) 0.001). Furthermore, the different heat treatments significantly (\(P<\) 0.001) affected its content, and, in the same way, in both feeds (Table 4). Thus, the highest concentration was found for grilled samples (4.68 and 5.73 AU \(\times\) 10\({}^{6}\)/g dry matter for CH and CF pig samples, respectively), while frying did not lead to their formation in CH slices, and, in the case of CF samples, this treatment generated the lowest quantity (1.12 AU \(\times\) 10\({}^{6}\)/g dry matter). According to [PERSON] [73] and [PERSON] et al. [15] it was found from Pearson test that 2-heptanone was also positively correlated with TBARS index (r = 0.747; \(P<\) 0.001 for CH samples; and r = 0.688; \(P<\) 0.001 for CF slices). To finish, the different presence of furan, 2-pentyl, is noted in accordance with the diet supplied. In that way, this substance was significantly (\(P<\) 0.01) higher in CH slices, apart from fried samples where this furan was not detected (Table 4). This incident could be justified by the inclusion of chestnut in the pig diet; because these fruits have a high concentration of linoleic acid [18], and this fatty acid can be decomposed by oxidation materializing furan, 2-pentil [75].