## 3 Results and Discussion
### Volatile Compound Profiles in Cheeses
Regarding aldehydes, four (benzaldehyde, dodecanal, hexanal and nonanal) were more present (\(p<0.05\)) in PDO Cantal cheeses compared to PDO Salers cheeses. Such result should be modulated for hexanal, which presents significant interactions with cow breed's milk. Aldehydes may have an important influence on cheese flavor because most of them are detected in other cheeses [33]. These are transitional compounds in cheese because they are quickly reduced to primary alcohols or oxidized to corresponding acids [45]. Benzaldehyde characterized Cantal cheeses and was the most abundant cyclic compound found in the present study. Benzaldehyde has previously been detected in other cheeses [46]. This compound originates from the oxidation reaction of cinnamic acid or phenylacetaldehyde and develops an aromatic note of bitter almond [47]. Only one terpene was detected (limonene), and no statistical difference was observed when comparing Cantal and Salers cheeses in our study. Terpene profile differences originated from multiple factors, such as physical, chemical or microbial mechanisms involved during the cheese-making process [12]. In addition, microbiological flora may have induced different chemical reactions on terpene molecules. A link has also been identified with the farm environment and, in particular, pasture feeding [48]. Regarding the other five VOCs differentiating the cheese categories, two (2(3H)-furanone, dihydro-5-pentyl; 1,3-dioxane, 2-ethyl-2-4-5-trimethyl) were only present in PDO Salers cheeses, and the other three (2,2,4-trimethyl-1,3-pentanediol diisobutyrate, propane 1,2-dimethoxy and pyrazine trimethyl) were more present in PDO Cantal cheeses compared to PDO Salers cheeses. Propane, 1,2-dimethoxy and pyrazine, trimethyl could not be generalized to differentiate cheese categories due to their significant interaction with cow breeds' milk. To better visualize the volatile composition among the twelve cheeses, analyzed in duplicate, a PCA was performed (Figure 2) on the totality of the VOCs. The first two components explained about 58% of the total variance. Figure 2B,C show the confidence ellipsoids representing the variability of the results over 12 cheees (with replication). Concerning the effect of different cow breeds' milk, the ellipses overlapping indicated a bad discrimination between cheeses made from different types of milk (Figure 2B). In contrast, the effect of the cheese category (Figure 2C) showed a good and clear distinction between both cheeses. Cantal cheeses and Salers cheeses were clearly separated based on the first component, dominated by previously described compounds such as acetoin, benzaldehyde, dodecanal and phenol. Taking into consideration the size of the ellipse, a broader chemical diversity could be observed in Salers cheeses vs. Cantal cheeses. More precisely, H_Salers cheese was described by elevated relative contents of phenylethanol and 3-methyl butanoic acid. In contrast, in the Cantal category, this chemical diversity was less pronounced. The differences observed between each cheese category could be explained by different external factors, such as raw milk or the ruminant diet. Indeed, raw milk is an uncontrolled source of microflora; the most obvious source of variability appears to be microbial. It is well known that the potential for microflora to generate flavor variability is greater than the potential variability from different breeds or on-farm practices, especially when other aspects of cheese-making, such as curd composition and ripening conditions, are similar [49; 50]. Figure 2: _Cont._  
Another explanation for the differences between the two categories is the use of sheaves. In fact, the sheaf contains a microbial biofilm on the walls of the sheaf, which favors the transfer of microorganisms from the sheaf to the milk, which, in turn, favors the development of certain volatile compounds [51].