## 3 Results and Discussions
### Microbiological Analysis  
In the _gulupa_ pulp, no enterobacteria, aerobic mesophilic bacteria, or psychrophilic bacteria were found, neither in the control nor in the samples treated with ultrasound. _Gulupa_'s low pH (pH 2.81) may act as a retardant or growth inhibitor of pathogenic bacteria, which generally require substrates with pH values higher than 4.6. Acidic foods such as citrus fruits and their products are considered safe for direct consumption because the survival of microorganisms that generally attack food and are pathogenic for humans hardly grow at low pH levels [31]. Additionally, the growth and development of microorganisms such as bacteria require media rich in protein and low in sugar, contrary to those found in _gulupa_ pulp, whose protein content ranges between 0.7 and 0.9% in the different stages of maturation [5], which may mean that the _gulupa_ is a problematic substrate for the development of bacteria. A significant decrease in yeast content was observed due to the effect of ultrasound for the 30 kHz treatments at 20 and 30 min (1.2-1.3 log CFU/mL) and all 40 kHz treatments (1.5-2.1 log CFU/mL) concerning the control (Table 6). This fact is attributed to the ultrasound treatment, where the production of cavitation bubbles in the fluid causes a higher temperature and pressure in the cavitation region, thus achieving the inactivation of the yeasts [32]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Power (kHz)**} & \multirow{2}{*}{**Time (min)**} & \multicolumn{6}{c}{**Day after Treatment**} \\ \cline{3-8}  & & **0** & **4** & **8** & **12** & **16** & **20** \\ \hline \multirow{4}{*}{30} & Control & 4.2 \(\pm\) 0.2 cD & 3.5 \(\pm\) 0.2 bC & 3.2 \(\pm\) 0.2 bD & 2.9 \(\pm\) 0.2 aC & 2.8 \(\pm\) 0.2a & 2.8 \(\pm\) 0.2a \\  & 10 & 4.2 \(\pm\) 0.2 dD & 2.8 \(\pm\) 0.2 cB & 2.6 \(\pm\) 0.2 bC & 2.5 \(\pm\) 0.2 bB & 2.0 \(\pm\) 0.2a & n.d \\  & 20 & 3.0 \(\pm\) 0.2 cC & 2.7 \(\pm\) 0.2 bB & 2.7 \(\pm\) 0.2 bC & 2.4 \(\pm\) 0.2 aAB & n.d & n.d \\  & 30 & 2.9 \(\pm\) 0.2 cC & 2.6 \(\pm\) 0.2 bAB & 2.5 \(\pm\) 0.2 bC & 2.3 \(\pm\) 0.2 aA & n.d & n.d \\  & 10 & 2.7 \(\pm\) 0.2 cB & 2.5 \(\pm\) 0.1 bA & 2.3 \(\pm\) 0.2 aB & 2.2 \(\pm\) 0.2 aA & n.d & n.d \\
40 & 20 & 2.5 \(\pm\) 0.3 cB & 2.4 \(\pm\) 0.2 bA & 2.0 \(\pm\) 0.2 aA & n.d & n.d & n.d \\  & 30 & 2.1 \(\pm\) 0.2A & n.d & n.d & n.d & n.d & n.d \\ \hline \hline \end{tabular} Data expressed as mean \(\pm\) standard deviation of three repetitions. In the same row, different lowercase letters indicate statistically significant differences between treatment days (\(p\) < 0.05). In the same column, different capital letters indicate statistically significant differences between the treatments (\(p\) < 0.05). Legend n.d not detected.  
\end{table} 
Table 6: Yeast count (log CFU/mL) during storage at 4 \({}^{\circ}\)C of _Passiflora eulis f. edulis_ Sims (_gulupa_) pulp subjected to low-frequency ultrasound treatments. Ultrasound is considered to act on microorganisms' hydrophobic surfaces, which help collision cavitation bubbles and cause severe damage to the cell wall and, consequently, microbial inactivation [60]. However, some authors state that yeast cells are relatively rigid and are not easy to break, due to the cavitation effect, so the inactivation can also be attributed in large part to the formation of free radicals such as hydrogen peroxide and the release of intracellular proteins [61]. Additionally, the initial inactivation could also be favored by the low pH of the _gulupa_[9], e.g., bacteria, as indicated by [PERSON] and [PERSON] [62]. Microbe inactivation by ultrasound is sufficient when used combined with other decontamination techniques such as extremes of pH. As occurred in this study, a low pH of _gulupa_ pulp may increase the antimicrobial efficiency of sonication, possibly attributed to the improved hydroxyl radical production. The results found were higher than those reported by [PERSON] et al.