## 3 Results and Discussion
### Volatile Compound Profiles in Cheeses
This compound was also identified in [PERSON] cheeses by [PERSON] et al. (2005) [6]. Butanoic acid is a major aroma compound with a cheesy, sharp aroma, and it plays an important role in the flavor of many cheeses [27]. The source of the butanoic acid in the cheese essentially results from lipolysis by endogenous milk-based or microbial-origin lipases, but it can also result from the metabolism of deamination of amino acids and lipid oxidation [5; 28]. Butanal, 3-methyl-is more abundant in cheeses made with _[PERSON]_ milk than those made from other breeds' milk. This compound is associated as a key flavor compound with many hard and semi-hard cheese varieties and is derived from the degradation of leucine. It is known that those compounds can be produced by different lactic acid bacteria, such as _Lactococcus lactis_, _Streptococcus salivarius_ and _Lactobacillus delbrueckii_. Those species are part of the raw milk flora (in raw milk cheese) and starter cultures [29], which could explain why this compound is more abundant in the cheeses made with [PERSON] milk. The cheese categories showed bigger differences in chemical families compared to the cow's breed origin of milk. PDO Cantal cheeses were characterized by ketones (42.8%), followed by alcohols (34.4%) and acids (19.34%). In contrast, Salers cheeses were characterized by a high content of alcohols (55.1%), followed by ketones (19.8%), acids (13.7%) and esters (10.8%). The main VOCs identified (Table 3) from the experimental cheeses were consistent with those previously reported in Cantal-type or Salers-type chees [6; 30]. In our study, forty-seven VOCs enabled us to differentiate PDO Cantal cheeses and PDO  
Figure 1: Average percentages of classes of volatile compounds identified for each condition of cheese category: (**A**) Cantal cheeses vs. (**B**) Salers cheeses and cow breeds’ milk: (**C**) OB_M vs. (**D**) Salers_M (OB_M = other breeds’ milk; Salers_M = Salers milk). Salers cheees (Table 3). Thirty-seven presented no interactions with milk from different cow breeds. Among them, esters were the family that presented the highest number of compounds compared to the other analyzed volatile families, enabling us to discriminate PDO Cantal cheees and PDO Salers cheees. Among the list of twenty-two esters analyzed, seventeen esters were systematically higher in PDO Salers compared to PDO Cantal cheees. In that list, three compounds (acetic acid ethenyl ester, butanoic acid 3-methylbutyl ester and isobutyl acetate) could not be used to differentiate the cheese categories due to their interaction with cow breeds' milk. And ten were specific to PDO Salers cheees, such as ethyl-9-decenoate; acetic acid; 2-phenylethyl ester; butanoic acid; 2-methyl propyl ester; butanoic acid, 3-methyl-ethyl ester; butanoic acid, 3-methylbutyl ester; dodecanoic acid, ethyl ester; isoamyl lactate; isobutyl acetate; isopentyl hexanoate and propanoic acid, 2-hydroxy-ethyl ester. Butanoic acid, 3-methyl-ethyl ester and isobutyl acetate could not be generalized due to the significant interaction with cow breeds. Esters represent a class of VOCs produced by esterification reactions between alcohols, produced during lactose fermentation or amino acid catabolism or indirectly derived from FFA metabolism [31]. Generally, the type and concentration of esters found in cheees vary according to cheese varieties and process conditions. Ethyl esters are known for their important role in the formation of a fruity character in cheese [32]. As suggested by [PERSON] et al. (2009) [30], the ripening time has an impact on the amount of some volatile compounds found between three and six months for Cantal cheees. In the same way, relative amounts of volatile compounds in Salers and Cantal cheees evolved upon cheese ripening (up to 6 months) with no specific observable trends, as previously observed in Cheddar cheees [32]. [PERSON] et al. (2005) [6] showed that the aromatic profile of Salers cheees (150 days of ripening time) was modified according to the indigenous flora used.