## 3 Discussion
[62] identified 36 volatile compounds (14 ketones, 11 aldehydes, six alcohols, and five other compounds) in fermented milk, but as the milk fat content increased the level of ketone compounds increased; in addition, 14 constituents (eight ketones and six aldehydes) were responsible for the aroma profile. Additionally, in the research carried out by [PERSON] et al. [63] on the release profile of flavor compounds from sour cream, the authors found that 31 components such as esters (nine), aldehydes (six), acids (three), alcohols (six), ketones (five), and other substances (two) were present in the volatile fractions of the samples. Moreover, three characteristic molecules (ethyl acetate, 1-octen-3-one, and caproic acid) increased their content as the fermentation time increased. In contrast, [PERSON] et al. [64] identified 53 and 43 volatile compounds from skimmed milk fermented by two LAB strains (_S. thermophilus_ and _Lactobacillus delbrueckii_ ssp. _bulgaricus_); these compounds were mainly 11 acids (e.g., C\({}_{2:0}\), C\({}_{4:0}\), C\({}_{6:0}\)-C\({}_{10:0}\), benzoic acid, etc. ), 10 aldehydes (e.g., nonanal, 2-methylundecanal, (_E,E_)-2,4-heptadienel, benzaldehyde, acetaldehyde, etc. ), 13 ketones (e.g., 2-undecanone, 2-nonanone, 2-heptanone, acetoin, etc. ), 13 alcohols (e.g., 1-nonanol, 2-nonanol, ethanol, etc. ), seven esters (e.g., \(\delta\)-nonalactone, ethyl caprate/caproate/butyrate, etc. ), and 19 hydrocarbons (including terpenes, humulene,caryophyllene, C\({}_{11}\)-C\({}_{13}\), xylene, toluene, etc.). The authors established that the volatile composition of the fermented milk product depended on the LAB strains (starter cultures) as well as whether they were used individually or in combination. Lastly, [PERSON] et al. [16] determined the volatile constituents (34) related to the aroma profiles of 32 commercial sour cream samples; as a result, 13 components (alkyl sulfides, ethyl(methyl)-alkenyl(alkyl)-ketones, aldehydes, SCFAs, etc.) were responsible for the flavor of 31-32 samples. Based on the concentrations of the 34 constituents, the increasing order of contribution to aroma was acetic acid > acetaldehyde > butyric acid > acetoin > octanal > 2-butanone > nonanal; furthermore, the authors stated that the profiled aroma compounds were derived (by biochemical reactions) from constituents inherent to the RM or its thermal treatment. The comparison between the literature reports mentioned above and the results of this research showed relevant differences and some similarities; i.e., the volatile profiles of SC samples were mainly characterized by ethyl esters (as the most abundant constituents, e.g., ethyl acetate, ethyl caprate, etc. ), followed by fatty (including short-chain (C\({}_{2:0}\)-C\({}_{5:0}\) acids) and unsaturated) and aromatic acids, alcohols (ethanol, isoamyl alcohol, (\(2E\))-tridecen-1-ol, etc. ), sesquiterpenes, aliphatic aldehydes, and acetoin. Other contributing molecules were methyl alkyl ketones (2-pentadecanone, 2-tridecanone, 2-nonanone, etc. ), lactones (8-dodecalactone and \(\delta\)-decalactone), and benzenethanol. This composition showed similarity with the reports by [PERSON] et al. [64] and [PERSON] et al. [61] in specific constituents (C\({}_{10:0}\), C\({}_{8:0}\), benzoic acid, C\({}_{6:0}\), C\({}_{4:0}\), C\({}_{2:0}\), nonanal, 2-methylundecanan, 2-undecanone, 2-nonanone, 2-heptanone, acetoin, 1-nonanol, 2-nonanol, ethanol, ethyl caprate, ethyl caprate, ethyl butyrate, humulene, carryophyllene, \(n\)C\({}_{11}\)-\(n\)C\({}_{13}\) hydrocarbons, and toluene) but differences (in most chemical structures) with that reported by [PERSON] et al. and [PERSON] et al. [62; 63]. Finally, the contrast between the composition determined by [PERSON] et al. [16] and this report only showed similarity in the content of acetoin and C\({}_{2:0}\) and C\({}_{4:0}\) acids.