## 2 Results
### Chemical Composition of Volatile Fractions  
The chemical constituents positively identified (83-99%) in the volatile fractions of SC and RM samples by SDE/SPME-GC-FID/MSD (Figures S3 and S4) are listed in order of elution in Tables A1 and A2. Thus, the volatile profiles of the RM and SC samples were, respectively, composed of 48-78 and 65-100 constituents. The common major constituents (1-46% of the relative amounts by SDE--Table A1) found in the volatile fractions of milk samples were nine fatty acids (C\({}_{8.0}\)-C\({}_{16.0}\), including C\({}_{10:1}\) and C\({}_{14:1}\)) together with benzoic acid. However, some minority non-acid compounds, related to the organoleptic properties of RM, were also recognized, e.g., six methyl alkyl ketones, five cyclic esters (lactones), and four aliphatic aldehydes. In addition, some miscellaneous compounds such as two sesquiterpenes (\(\beta\)-caryophyllene, \(\alpha\)-humulene), 10 linear/branched hydrocarbons, one aromatic hydrocarbon, and one aromatic alcohol (benzenethanol) were present. Non-parametric ANOVA of these data indicated that there were no significant differences within each group [type of compounds (\(p\): 0.4544, K-W test--Table S14)] for all RM samples, but there were differences (\(p\): \(<\)0.05, Friedman test--Table S15) in the chemical composition of sample L1 compared to the other milk samples (no significant differences between them, \(p\): \(>\)0.05). Furthermore, the volatile fractions by HS-SPME of the RM samples (Table A2) were mainly represented by C\({}_{10:0}\), C\({}_{8.0}\), C\({}_{6.0}\), and C\({}_{12:0}\) fatty acids together with limone, the C\({}_{2:0}\) and C\({}_{4:0}\) acids, isoamyl alcohol, 2-nonanone, benzoic acid, the C\({}_{14:0}\) and C\({}_{14:1}\) fatty acids, acetone, and pentanol. Other types of compounds related to milk flavor were also present: five methyl alkyl ketones, four cyclic esters, two sesquiterpenes, seven linear/branched hydrocarbons, benzenethanol, and myristylaldehyde. It is important to mention that ester-type compounds (ethyl caprate, ethyl laurate, and ethyl myristate) were identified in the milk samples, as well as monoaromatic hydrocarbons (toluene and styrene), and a high content of 2-nonanone in milk sample L7. As with the SDE method, the non-parametric ANOVA of HS-SPME data showed the same trend; i.e., there were differences (\(p\): \(<\)0.05, Friedman test--Table S15) for the composition of sample L1 versus the remaining milk samples (no significant differences between them, \(p\): \(>\)0.05), but there were no differences within each group [type of compounds (\(p\): 0.4544, K-W test--Table S14)] for all samples. Non-parametric ANOVA applied to the compositions of volatile fractions (average relative amounts per compound family for all RM samples) for both SDE and HS-SPME methods revealed no significant differences within and between all samples (Friedman: \(p\): 0.6507; K-W: \(p\): 0.4544--Tables S16 and S17). Considering the chemical compositions of the volatile fractions by SDE (Figure S4A) of the SC samples, these were mainly typified by 13 fatty acids (including short-chain) [(3-Me)-C\({}_{4:0}\) (iso-C\({}_{5:0}\)), (2-Me)-C\({}_{4:0}\), C\({}_{5:0}\), C\({}_{6:0}\)-C\({}_{16:0}\), C\({}_{10:1}\), and C\({}_{14:1}\)], six ethyl esters (e.g., ethyl caprate, ethyl 9-decenoate, etc. ), three aliphatic alcohols (e.g., (\(2E\))-tridecen-1-ol, etc. ), six methyl alkyl ketones, four aliphatic aldehydes, five sesquiterpenes (e.g., selimane, cadinene isomers, etc. ), eight linear/branched hydrocarbons, five lactones, one aromatic acid, and one aromatic alcohol. Other relevant molecules (volatiles) were also identified in the majority (50-75%) of the SC samples, i.e., 11 esters (e.g., ethyl caprylate, ethyl (9Z)-tetradecenoate, ethyl caprate, \(\beta\)-phenethyl acetate, ethyl (9Z)-heptadecenoate, etc.