## 2 Results
### Differences and Similarities Between Constituents of Volatile Fractions by PCA and LDA
71% of the data variability; the contributing variables to PC1 were LHCs and MET-ALC-KETs (0.98 for each) and branched hydrocarbons (BHCs) and ALIP-ALDs (0.96 for each), while for PC2, these were ESTs (0.86), FSFAs (0.82), and free unsaturated fatty acids [FUFAs (\(-\)0.74)]. As a result of this analysis, three groupings could be established: (i) L4 and L6, (ii) L3, and (iii) L1, L2, L5, L7, and L8; among them, L4 and L6, L2 and L8, and L1 were consistent with the hypothesis of compositional similarity based on the same manufacturing process, but L5, L7, and L3 apparently were not. Considering the LDA, the two canonical axes 1 (58.0%) and 2 (36.0%) were able to explain ca. 94% of the data variability; the most discriminating variables for both axes (1 and 2) were FSFAs (\(-\)4.70 and 7.21) and ESTs (4.42 and \(-\)7.17). In addition, four groupings were observed in the plot: (i) L3 and L7, closely related to (ii) L1, L2, and L8, (iii) L5 and L6, and (iv) L4. Considering the compositional similarity hypothesis, then, L3 and L7 and L2, L8, and L1 were consistent, but L4, L5, and L6 were not. Finally, the results of the \"two-sample inference (F-test of equality of variances)\" for all data, grouped by matrix types (RM and SC), are listed in Table S21. According to the table, seven types of compounds showed significant differences (\(p<\)0.05) between the samples and were, therefore, the differentiating and outstanding component types: free saturated fatty acids, esters, aliphatic aldehydes, methyl alkoxyl ketones, aromatic aldehydes and acids, and branched hydrocarbons. Box plots were also applied to all data, comparing matrix types versus compound types (Figure 5). From these plots, it could be observed and inferred that the content (i) distinctly decreased for SFSAs, FUFAs, and BHCs, (ii) notably increased for ESTs, ALIP-ALCs, MET-ALK-KETs, MET-ALC-KETs, and SESQs, (iii) slightly decreased for SCFAs, LHCs, and AR-HCs, (iv) increased slightly for AR-ACIDs, ALIP-ALDs, AR-ALCs, AR-ALDs, and MONOTs, and (v) did not change for LACTs in SC samples compared to milk samples. This interpretation is important because it showed the formation of ESTs from SFSAs, FUFAs, and SCFAs and ALIP-ALCs; i.e., the products (esters) increased and the precursors/ reagents (acids and alcohols) decreased. Figure 4: PCA **(A)** and LDA (**B**) plots relating SC sampling points (locations) to the composition of volatile fractions. SCFAs: short-chain fatty acids (\(\leq\)C\({}_{6}\)), FSFAs: free saturated fatty acids (\(\geq\)C\({}_{7}\)), FUFAs: free unsaturated fatty acids, ALIP-ALDs: aliphatic aldehydes, ALIP-ALCs: aliphatic alcohols, MET-ALK-KETs: methyl alkyl ketones, AR-ALDs: aromatic aldehydes, AR-ALCs: aromatic alcohols, AR-ACIDs: aromatic acids, ESTs: esters, LACTs: lactones, MONOTs: monoterrepenoids, SESQs: sesquiterpenenes, LHCs: linear hydrocarbons, BHCs: branched hydrocarbons, AR-HCs: aromatic hydrocarbons, HTC-ALCs: heterocyclic alcohols, PhOHs: phenols, HTC-ETs: heterocyclic ethers, MET-ALC-KETs: methyl alcohol ketones, AL-ACIDs: aliphatic acids, and DIKETs: diketones. L: locations where suero costého samples were collected; L1–L8: locations listed in Table S20.