## 2 Results and Discussion
### Impact of Oral Microbiota on Glycosidic Precursors (GP)
The volatile compounds with hydroxyl groups are usually linked to sugars, but carboxylic acids can \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compound \({}^{\,\bullet}\)**} & \multirow{2}{*}{**R1D-wa**} & \multirow{2}{*}{**Aerobic Conditions (C1, Amount in ppm) \({}^{\,\bullet}\)**} & \multirow{2}{*}{**Anaerobic Conditions (C2, Amount in ppm) \({}^{\,\bullet}\)**} \\ \cline{5-8}  & & & **A1** & & **A2** & **A3** & **A1** & **A2** & **A3** \\ \hline V1 & 2-Methyl-1-propanol \({}^{\,\text{b}}\) & 1085 & 0.00315 & 0.00168 & 0.00297 & 0.00178 & 0.00064 & - \\ V2 & 1-Butanol \({}^{\,\text{b}}\) & 1176 & 0.02510 & 0.01480 & 0.03870 & 0.02450 & 0.01400 & 0.03430 \\ V3 & 2-Hexanol \({}^{\,\text{b,d}}\) & 1197 & 0.05350 & - & 0.05800 & 0.01510 & - & - \\ V4 & 3-Methyl-1-butanol & 1213 & 0.03060 & 0.00476 & 0.05430 & 0.01620 & 0.00406 & 0.02960 \\ V5 & Hexanol \({}^{\,\text{c,d}}\) & 1368 & 0.02200 & 0.03800 & - & 0.19100 & - & - \\ V6 & 2-Ethyl-1-hexanol \({}^{\,\text{b}}\) & 1494 & 0.14400 & 0.20400 & 0.15800 & 0.13100 & 0.14500 & 0.13700 \\ V7 & 4-Butoxy-1-butanol \({}^{\,\text{b}}\) & 1691 & 0.01680 & 0.000707 & 0.01270 & 0.01360 & 0.00874 & 0.00044 \\ V8 & Isomomally acetate \({}^{\,\text{b,d}}\) & 1159 & 0.02500 & - & 0.03220 & - & - & - \\ V9 & Ethyl hexanoate \({}^{\,\text{c}}\) & 1238 & 0.00592 & 0.00304 & - & 0.00877 & 0.00207 & - \\ V10 & 4-Methyl-2-heptanone \({}^{\,\text{b}}\) & 1250 & 0.00898 & 0.00805 & - & 0.00550 & 0.00269 & - \\ V11 & Benzaldehyde & 1528 & 0.42000 & 0.14800 & 0.54000 & 0.23900 & 0.16500 & 0.25000 \\ V12 & 4-Ethyl benzaldehyde \({}^{\,\text{b}}\) & 1786 & 0.02020 & 0.01430 & 0.02860 & 0.01960 & 0.01450 & 0.02200 \\ V13 & Acetic acid & 1452 & 0.08790 & 0.01740 & 0.10900 & 0.01150 & 0.01920 & 0.05060 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Volatile compounds detected at the initial time (t = 0 h, T1) of the incubation of _P. Friedrichsthalianum_ glycosidic extract with oral microbiota isolated from saliva under different conditions. also be linked as glycosides. This could be an explanation for the presence of an ester in this experiment. Table S1 in the Supplementary Material shows (as an example of what happens with the 13 volatiles) the results of a three-way analysis of variance carried out with the values of 2-methyl-propanol and taking as factors the assay (three levels), experimental conditions  
Figure 1: **(A)** Grouping of the volatile compounds obtained in the assays at different times (T1–T4) according to the incubation conditions (aerobic or anaerobic), by means of discriminant statistical analysis (DSA) by the square method. (**B**) Loading plot of linear discriminant analysis for volatile compounds found in different assays (A1, A2, and A3). A1 = GP incubation with oral microbiota; A2 = Only GP without oral microbiota; A3 = Only oral microbiota without GP. (two levels), and time (four levels). A remarkable aspect is an interaction between the factors (assay, condition, and time). Similar results (not shown to save space) were obtained with the other 12 volatile compounds. This situation indicates that it is convenient to complement discriminant analyses with others that help to visualize in an integrated way the variability of the compounds concerning the combination of the levels of the three factors (assay, condition, and time of hydrolysis). To this end, a principal component analysis (PCA, Figure 2) was carried out with all available information, to analyze the relationship between the compounds and factors simultaneously. Figure 2 shows the results regarding the two first components, which explain 51.5% of the variability of the analyzed data. The most notable results are interpreted as follows. The records of assay A1 (GP+OM), under anaerobic (C2) conditions, at times T3 and T4 (24 and 72 h), are associated with values above the average in butanol (V2) and hexanol (V5), indicating that these alcohols are produced by hydrolysis of glycosidic precursors by the oral microbiota.