## 3 Results and Discussion
### Effect of Breed and Finishing Diet on Volatile Compounds
#### 3.2.6 Esters, Ethers, Furans, Nitrogen Compounds and Sulfur Compounds  
Table 4 shows the effect of breed and finishing diet on compounds belonging to the ester family. In this study, six esters were identified in our samples and the total content was shown to be unaffected by breed (\(p>0.05\)). In fact, although four out of the six compounds identified presented significant differences (\(p<0.05\)), the esters with the majority amounts (vinyl butyrate and caproic acid vinyl ester) reported similar values in both BU and JN fools. Comparing our data with literature, any esters detected in our fools coincided with  
those found by other authors, studying GM \(\times\) HB and GM raw foal meat [25; 26; 27], probably due to the different breeds employed. Additionally, the total ester content occupied 4.22 and 4.95% (for BU and JN fools, respectively) (Figure 1) of the total volatile compounds, corresponding to the fourth most abundant family detected in both breeds. These outcomes disagree with those published by previous studies in raw foal meat [25; 26; 27], where esters represented the most plentiful compounds. On the other hand, data showed that the type of diet significantly influenced the total esters content, where the D1 group recorded significantly higher values than the D2 group (\(p<0.001\)). As regards the singular substances, vinyl butyrate and caproic acid vinyl ester (the most abundant esters) followed the same trend. Similarly, previous studies [54; 64] observed this tendency, indicating that animals fattened with conventional concentrates presented greater ester contents. These differences could be explained by the variability of the fatty acid profile of fools, since esters arise from the esterification of several carboxylic acids in meat [25; 26; 27; 74]. In this regard, as shown in Table 2, D1 and D2 reported significantly different lipid profiles, revealing that 20 out of the 22 fatty acids identified were affected by the type of diet. Thus, these outcomes could justify the behavior of the esters in our study. Moreover, esters are defined as very fragrant compounds [26] which are able to modulate the global flavor owing to their low odor thresholds, imparting fruity notes, especially those composed by short-chain acids [59], while esters formed from long-chain acids provide a slightly fatty odor [84]. However, this class of compounds represented the fourth most abundant family for D1 and D2 groups, considering the total amounts of volatile compounds (Figure 1). Therefore, although the fraction of esters to the total volatile compounds was relatively high (4.97 in D1 fools and 4.24% for D2 fools) (Figure 1), it is complex to affirm that their presence may contribute to the overall aroma of the foal meat. As regards the four groups of treatment, JN-D1 fools produced the highest amounts of esters, followed by BU-D1 ones, while JN-D2 showed the lowest levels, confirming the data discussed above. In addition, statistical analysis showed the presence of significant interactions among the main factors (breed \(\times\) finishing diet) in all variables, except for dibutyl sulfate. With respect to the ether family, only four different compounds were identified in the _longissimus thoracis et lumborum_ muscle of fools (Table 4). Breed affected both the total content and each individual ether, showing in all cases significantly higher (\(p<0.05\)) values in BU fools, apart from oxirane, tetramethyl-. Nevertheless, despite this marked tendency, this family has not been detected previously in raw foal meat [25; 26; 27]. A recent study related its presence in meat to possible environmental contamination, since the vapors of certain ethers are employed as fumigants to treat the soil against insects and mites [61]. Thus, their use as biomarkers may be inappropriate. Moreover, considering the ether contribution to the total volatile profile, these substances only represented 0.82 and 0.61% of the total content in BU and JN fools, respectively (Figure 1), being clearly irrelevant in the aromatic profile of foal meat.