## 2 Results and Discussion
### Impact of Oral Microbiota on Glycosidic Precursors (GP)  
The oral microbiota is one the most complex bacterial communities associated with the human body; the SHI (bacteriological growth medium) culture medium was used because it is specific for this type of microorganism, very rich in nutrients, and it thus ensures the growth of a larger population of culturable oral bacteria [16]. The saliva samples of three volunteers were mixed because the variability of the oral microbiota of each individual greatly affects the hydrolysis of the aroma precursors [13]. In this experiment, only the microbiota isolated from raw saliva was used. To verify that bacteria from the oral cavity were able to hydrolyze the fruit glycosides under the established conditions, the standard octyl-\(\beta\)-D-glucopyranoside (20 ppm) was incubated as the positive control of the experiment. This glycoside was incubated separately under two conditions, aerobic (C1) and anaerobic (C2), and in both cases, the volatile compounds released were analyzed at four times, T1-T4 (0, 2, 24, and 72 h, respectively). The hydrolysis of this compound released 1-octanol under anaerobic conditions only at 24 h (2.09 ppm). This compound was identified by comparison of its MS and retention index (RI\({}_{\text{DB-Wax}}\) = 1599) with those of the corresponding standard. Under aerobic conditions, 1-octanol was also detected, but at a lower intensity (not quantifiable). These results corroborate the hydrolytic capacity of oral cavity bacteria on glycosidic-type compounds, as already shown previously [13]. In the assays carried out with the GP extract from _P. Friedrichsthalianum_ fruit, 13 volatile compounds were detected after the incubation assays. These compounds were measured at four times, T1-T4, but in Table 1, only the data at initial time T1 are reported. Among the compounds, it seems that hexanol comes from the hydrolysis of glycosidic precursors because it was not detected in the control experiments without GP under anaerobic conditions (A3C2) and aerobic (A3C1) conditions. The volatile compounds found under anaerobic conditions in the A3 assay (only oral microbiota) were: 1-butanol, 3-methyl-1-butanol, acetic acid, 2-ethyl-1-hexanol, benzaldehyde, 4-butoxy-1-butanol, and 4-ethyl benzaldehyde; these may come from the decomposition of the SHI medium, which has a complex composition including peptone, tryp protease, yeast extract, sucrose, arginine, mucin, and sheep blood, among other constituents [16]. The mild conditions of incubation release a portion of these volatile compounds, but the amount was higher in the presence of oral microbiota. It was also determined that the highest production of volatile compounds was at 24 h when the oral microbiota was able to hydrolyze the glycosides; after that, the amount of volatile compounds started to decrease. Figure 1A,B show the results of discriminant analyses. Figure 1A used the conditions (aerobic or anaerobic) as a qualitative variable and shows that high amounts of hexane, ethyl hexanoate, and butanol were produced under anaerobic conditions. In contrast, higher amounts of the other compounds were obtained under aerobic conditions. This finding suggests that hydrolysis under anaerobic conditions is more effective in producing odorant compounds. On the other hand, Figure 1B used the assay (A1, A2, or A3, the meaning of which is explained in the footnote of Table 1) as a qualitative variable. According to Figure 1B, there is an overlap between the A1 and A2 assays; namely, there are similar amounts of some of the compounds in both assays (i.e., 4-methyl-2-heptanone). In the assay A1 (GP + OM), high values (above the mean) of hexanol and 4-butoxy-butanol were obtained. Additionally, above-average amounts of benzaldehyde, 2-ethyl-hexanol, and 2-methyl-propanol were obtained in the A3 assay (only oral microbiota). The volatiles released during different hydrolysis assays could be grouped into three clusters, showing that hexanol and ethyl hexanoate were only present in the A1 experiment.