## 3 Results and Discussion
### Analysis of Volatile Compounds
#### 3.3.2. Alcohols, Ketones and Aldehydes  
Table 3 shows the results for alcohols, ketones and aldehydes. The alcohols 2-butanol, 2-methyl-1-butanol, 2,3-butanediol, 2-butoxy-ethanol and 2,6-dimethyl-4-heptanol increased their levels throughout the ripening process, while 2-methyl-1-propanol, 3-methyl-1-butanol and phenyl-ethyl-alcohol showed higher abundance at day 0 of ripening and decreased during maturation. The most abundant alcohols at the end of the ripening were 2-butanol and 2,3-butanediol. The 2-butanol derived from 2,3-butanediol by the action of LAB [37], while the microbial reduction in acetoin could be the origin of 2,3-butanediol [38].  
Branched-chain alcohols 2-methyl-1-propanol and 3-methyl-1-butanol come from the reduction in branched-chain aldehydes and can be found in raw milk cheeses with intense proteolysis due to vegetable rennet [39] as is the case of \"Torta del Casar\". In fact, the former authors found 3-methyl-1-butanol as the major alcohol in \"La Serena\" cheese also made with vegetable rennet.  
The evolution of the production in alcohol compounds throughout the ripening process was very similar in the three analyzed batches (Table 3). In ripened cheeses the only significant (\(p\leq 0.05\)) differences between batches were the lower amount of 2-butanol and 2-methyl-1-propanol in batch Lc than in the control and Lg batches and the lower amount of 2,3-butanediol and 2-butoxy-ethanol in batch Lg than in the remaining batches.  
A low abundance of **ketones** was detected at the beginning of ripening, but significant increases for all detected compounds of this group were found after 90 days of ripening (Table 3). Ketones are abundant constituents of most dairy products and have typical odors and low perception thresholds [23; 40]. Thus, they could play an important role in the final aroma of \"Torta del Casar\" cheese. The 2-butane-one and 2-heptane-one were the most abundant ketones detected during ripening. Similar results have been found in \"Torta del Casar\" [40] and in other cheeses made with raw sheep's milk such as \"La Serena\" cheeses [39]. In the present work, 2-nonanone showed significantly higher abundance in batches Lc and Lg than in control batches, while 2-heptanone and 2-butanone were encountered in higher amounts in the control than in the LAB-inoculated batches (Table 3). These compounds are derived from \(\beta\)-oxidation of fatty acids, that are first oxidized to \(\alpha\)-ketoacids, which are further decarboxylated to their corresponding methyl-ketones with one carbon atom less, such as 2-heptanone, 2-nonanone and 2-butanone and finally the methyl-ketones can be reduced to secondary alcohols [41]. These compounds are necessary to cheese aroma, but since they are derived from \(\beta\)-oxidation of fatty acids, their production should be not stimulated, as could happen with the inoculation of selected LAB assayed, to avoid rancidity notes.  
As aldehydes, only 3-methylbutanal was identified throughout the ripening process. The aldehydes have been reported as minor compounds in these kind of soft cheeses, probably due to their instability since they are reduced to alcohols or oxidized to acids [40]. High concentrations of aldehydes are associated with the development of off-flavors in cheese [42] so an increase throughout the processing would be negative for the global aroma of this product. In the present work, a significant (\(p\leq 0.05\)) increase in 3-methylbutanal was observed throughout the ripening process in all the analyzed batches. The 3-methylbutanal, derived from the degradation of amino acid leucine [43; 44], is probably a consequence of proteolysis from vegetal rennet and microbial origin. Nevertheless, since no significant differences (\(p>0.05\)) between batches were detected in 3-methylbutanal in the present work, it seems that the selected _L. casei_ and _Lc. garivaee_ have a low impact on the production of this compound; at least no difference of the probable effect of LAB was present in control samples from contamination origin.