## 3 Discussion
All these compositional comparisons between SC and other similar dairy products based on milk fermentation (according to the available scientific literature) are necessary to support that the volatile chemical profile established for this artisanal product is original and unrepeatable, and to attribute to it one of the distinctive criteria that could give rise to its protected designation of origin. On the other hand, it should be noted that the main metabolites identified in SC samples are probably the result of lipolysis and/or \(\beta\)-oxidation of fatty acids (free fatty acids, methyl alkyl ketones, alcohols, and lactones), as well as glycolysis [metabolism of lactose (ethanol and SCFAs) and citrate (ethyl acetate and acetoin)] carried out during milk fermentation by LAB [9; 12; 60; 63]; thus, (i) the most representative constituents in the SC samples were ethyl esters (C\({}_{2}\)-C\({}_{12}\), C\({}_{10:1}\)(\(\Delta^{9}\))-C\({}_{18:1}\)(_cis_-\(\Delta^{9}\)), and C\({}_{13}\)-C\({}_{16}\)), which would contribute a floral and fruity note (or defect/off-flavor, depending on the concentration) to the SC [58; 65], and (ii) according to the results on LAB isolation from the majority of SC samples (data not yet published by the coauthors, but used with permission), the predominant strain was _Limosiactobacillus fermentum_ (along with _Lacticaseobacillus rhamnus_), which could be responsible for the production of specific volatile compounds in SC; but also, as these strains were different from the LAB strains reported by the authors mentioned during the discussion, the SC volatiles could differ from the chemical profiles described by them in their fermented milk products. Although the mechanism of ethyl ester biosynthesis by LAB in fermented milk has not been fully elucidated, it is hypothesized that the most likely route of biosynthesis could be via alcoholysis (by transferases) and/or hydrolysis (by esterases), depending on the strain involved in the fermentation, as well as the types of glycerides (acylglycerols) and alcohols [58; 66; 67]. In this manner, [PERSON] et al. and [PERSON] et al. [58; 67] stated that a rate-limiting factor for ethyl ester formation in fermented products (e.g., cheeses) was the ethanol availability (>ethanol content > ethyl ester of fatty acid content), but also the type of glycerides (e.g., tri-, di-, and mono-) present in the milk, as well as the water content and activity. Thus, considering _L. fermentum_ and _L. rhamn_ (strains isolated in most of the SC samples), both strains prefer di- and mono-glycerides as substrates for alcoholysis, producing esters between C\({}_{6}\)-C\({}_{14}\), mainly ethyl caprate (C\({}_{100}\)), ethyl caprylate (C\({}_{8,0}\)), and ethyl caproate (C\({}_{6,0}\)), as mentioned by [PERSON] et al. and [PERSON] et al. ; hence, this could explain why ethyl esters (up to C\({}_{14:0}\)) were mostly identified in the SC samples. Last but not least, _L. fermentum_ could produce some chemical constituents in non-negligible amounts (-5%) that would confer a less-palatable perception to SC, e.g., acetic acid (vinegar-like taste) and acetoin (strong butter-like taste) [68]; the tastes [related to C\({}_{2:0}\)/acetoin, which were identified in the SC samples (1.0-3.9%/0.7-3.4%)] described above are characteristic notes of the SC product (acid/sour and butter-like tastes, based on preliminary sensory testing--information not yet published, but used with permission). As for the PCA and LDA applied to the data, they allowed finding and demonstrating close relationships between the volatile fractions of the SC samples as a function of the manufacturing process and locations, as well as determining those main structural groups responsible for the possible identity profile of the SC.