## 2 Results and Discussion
### Volatile Compounds
#### 2.2.3 Aldehydes  
Aldehydes play an important role to the overall flavor of all fat products such as olive oil and dry-cured hams because of their low odor thresholds and high concentrations. SF showed the highest concentration of total aldehydes (21.27 mg/kg) while the lowest concentrations were found in BF (13.35 mg/kg) and ST (14.74 mg/kg) muscles (Table 3). This difference in concentration is due to the fact that saturated and monosaturated aldehydes result from lipid oxidation on the contrary to methyl-branched aldehydes (_i.e._, 3-methylbutanal), which are derived from the Strecker degradation reactions of free amino acids [29]. Thus, the lowest concentrations of 3-methylbutanal was found in SF, where the protein composition is not relevant (Table 3). The most abundant saturated aldehyde is octanal (Table 3) in all the locations, followed by nonanal (responsible for rancid attribute) and hexanal. The two latter are characteristics of rancid lipid matrices [17]. (_E_)-2-heptenal and (_E_)-2-nonenal were also quantified at high concentrations in the muscles. Hexanal is generated from the oxidative decomposition of linoleic acid [30] and its contribution to aroma depends on its concentration. Thus, hexanal at low concentrations has a pleasant and grassy aroma [31], which turns fatty at medium concentration and extremely rancid and tallowy at high concentrations [32]. At the concentrations determined in the analyzed hams, hexanal contributes to grassy odor and, perhaps, to a fatty perception in the case of some Iberian hams. Contrary to be suggested by other authors [33], hexanal is not related to the development of rancid flavors, and experience shows that its rancid aroma cannot be masked by other volatile compounds [32]. The polyunsaturated aldehyde (_E_,_E_)-2,4-decaional does not contribute to ham odor due to its high OT (2.50 mg/kg) (Table 2); with the exception of five hams, which presented concentrations higher than OT. Decanal and E-2-nonenal also showed concentrations (Table 3) lower than their OTs (Table 2). The contribution of heptanal and nonanal to aroma is also clear because of their high concentration values in most of the samples compared to their OT. Nonanal compound comes from the oxidation of oleic acid that is the most abundant unsaturated fatty acid in hams [21]. Saturated aldehydes are of utmost importance for the overall aroma of the hams. Lipid oxidation seems to be partially affected by the pig feeding/breed because the concentrations of hexanal, octanal and nonanal are higher in Iberian dry-cured hams than in the other samples (Table 2). In general, saturated aldehydes contribute to aroma with sensory descriptors such as green/grassy (hexanal), hamilke/fatty (heptanal), meat-like/fruity (octanal) and tallowy/rancid (nonanal) although with different intensity depending on the breed (Iberian _vs._ non Iberian hams). The monounsaturated aldehydes [(_E_)-2-heptenal, (_E_)-2-octenal, (_E_)-2-nonenal] results from lipid oxidation as well. Their concentrations were, in general, lower than those of saturated aldehydes but they contribute to aroma since their concentrations are higher than their OT in many of the samples. Concerning (_E_)-2-heptenal, the number of hams whose concentrations are higher than the corresponding OT is a little lower in SF than in the muscles. Its low OT (0.05 mg/kg) allows contributing to aroma with almond-like, green fruity and fatty sensory notes. The concentration of this compound has not allowed distinguishing non Iberian from Iberian hams, which could mean that these sensory notes would be of similar level in all the hams. The concentrations of (_E_)-2-octenal and (_E_)-2-nonenal are higher in SF but their low OTs (0.004 mg/kg and 0.15 mg/kg respectively) indicate that they contributes to the aroma in all the analyzed locations. Their concentrations alloweddistinguishing Iberian from non Iberian hams, and they contribute to the pungent and fatty sensory descriptors of Iberian hams.