## 3 Results and Discussion
### Effect of Breed and Finishing Diet on Volatile Compounds
#### 3.2.4 Aldehydes  
Table 4 shows the effect of breed and finishing diet on the nine different aldehydes and their total contents detected in the _longissimus thoracis et lumborum_ muscle. As showed in the table, the total content of these volatile compounds as well as most of individual aldehydes (6 of the 9 substances identified) were not affected by breed (\(p>0.05\)), presenting similar values in both groups. On the other hand, propanal, 2-propyl and heptanal showed higher (\(p<0.05\)) amounts in BU foals than JN ones. Researchers [22; 29] affirmed that propanal and heptanal derived from oxidizing linolenic and oleic acids, respectively. However, our results contrast with the similar content of these fatty acids found in meat from JN and BU foals (Table 2). Moreover, hexanal was the most plentiful in the two groups but it did not present significant (\(p>0.05\)) differences among them. Its predominance over the other compounds of this family can be related to the multiplicity of its synthesis pathways. In fact, some authors [29; 63] asserted that this compound can be generated both from oleic, linoleic and arachidonic acids, and through the deterioration of other unsaturated aldehydes, such as 2,4-decadienal. Considering the lipid profile of our samples (Table 2), although both breeds showed significantly different (\(p<0.05\)) values of C18:2\(n\)-6 and C20:4\(n\)-6, C18:1\(n\)-9, the predominant fatty acid among groups, presented similar values (\(p>0.05\)). Thus, our outcomes could be justified by the behavior of this more abundant fatty acid. With regards to the contribution of aldehydes over the total volatile content, this is the third most abundant family for both groups (Figure 1). Recent studies [25; 26] about raw foal meat agree with our outcomes, reporting this family as the third most plentiful in relation to the total volatile compounds detected. However, these studies showed greater total aldehyde content than ours. Lastly, it is worth highlighting that this class of compounds represents one of the main groups of volatile compounds owing to its low odor threshold, which can be critical for the aromatic profile of meat [64]. On the other hand, data showed that finishing diet significantly (\(p<0.001\)) affected total aldehyde amounts, being higher in the D1 group in comparison with D2 foals (314.05 _vs._ 204.31 AU \(\times\) 10\({}^{4}\)/g fresh meat, respectively). These data are consistent with those found by other authors [54; 65; 66], who detected higher amounts of these compounds in animals fattened with concentrates. Some researchers [65] related these results to the high level of linoleic acid usually present in the concentrates and the protective action of antioxidants (as carotenoids and tocopherols), abundant in forages, on the oxidation of fat from grass-fed animals [29]. Indeed, it was observed that concentrate-fed animals are more disposed to lipid oxidation than grass-fed animals, and this effect is due to the fact that forages are a natural source of antioxidants, presenting increased levels of vitamins A, C, and E, flavonoids, and carotenoids [28]. In fact, although grass-based diets and grass-fed animals are normally characterized by greater amounts of PUFA and, as a consequence, could be associated to higher lipid degradation [29], the antioxidants naturally present in forages reduce lipid oxidation rates and favor meat lipid stability [67; 68]. In this sense, our outcomes can be justified by the fact that silage, mainly constituting the D2 regime, probably present antioxidant compounds able to prevent meat lipid oxidation. Recent studies, in fact, demonstrated that conserved forage, as silage, is still a significant source of antioxidants [69; 70]. Moreover, the organic feed, used in diet 2,contained higher quantities of vitamin A (10,000 UI/kg) and E (15 mg/kg) in comparison with the conventional concentrates employed for the diet 1 (4800 UI/kg of vitamin A and 12 mg/kg of vitamin E) [3].