## 3 Results and Discussions  
### Titrable Acidity and pH  
The effect of ultrasound on the _gulupa_ pulp's pH did not show significant differences (\(p\) > 0.05) between the treatments during the 20 days of observation (average export and distribution). The values ranged from 2.72 \(\pm\) 0.01 to 2.86 \(\pm\) 0.02 (Table 1). Similar results were reported for juices with ultrasound treatment of _Citrus microcarpa_ (Lima kasturi) and _Malus domestica_ (Apple), where the changes in pH due to ultrasound treatment were meager, from 4.0 to 3.9 and from 2.68 to 2.66, respectively [31; 32]. The low pH values in the control and treatments that remain stable over time are mainly due to a self-regulating or buffering system involving citric acid [5; 33] like that found in _Passiflora edulis_ f. _flavicarpa_[34].  
In titratable acidity, there was a significant increase (\(p\) < 0.05) between day 0 and 4 for all treatments and the control (Table 2), due to the effect of obtaining the pulp, where the opening of the fruit begins to release some organic acids present at the level of the membranous sacs. After day four, small acidity changes were apparent, and at the end of the evaluation of the shelf life, the highest concentrations were presented in the control and the 30 min treatments. It is known that the accumulation of organic acids is the result of interactions between metabolism and vacuolar storage affected by environmental factors such as temperature and the opening of the fruit in this case [35]. As for other fruits, many factors affect the production of organic acids during the useful life of the _gulupa_ pulp.  
No differences were observed between the treatments' power (30 or 40 kHz), only in the exposure time. The 10 and 20 min treatments showed a significant decrease in acidity concerning the control (day 20), attributable to the deactivation of enzymes, which interrupts some metabolic processes involving organic acids, which is why the acidity could remain constant [36], observing a decrease concerning the control treatment. While the effect of ultrasound in treatments for 30 min was longer, it could favor the release of organic acids from the cell cytoplasm to the outside, caused by the rupture of the cell membrane when the enzymatic activity is decreased [37; 38]. Therefore, in 30 min treatments, the effect increased acidity, matching the natural maturation effect that was carried out in the control treatment.  
\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}{**Days after Treatment**} \\ \cline{3-8}  & & **0** & **4** & **8** & **12** & **16** & **20** \\ \hline Control & & 2.81 \(\pm\) 0.02 & 2.80 \(\pm\) 0.11 & 2.80 \(\pm\) 0.01 & 2.76 \(\pm\) 0.01 & 2.76 \(\pm\) 0.01 & 2.77 \(\pm\) 0.03 \\  & 10 & 2.72 \(\pm\) 0.01 & 2.79 \(\pm\) 0.01 & 2.75 \(\pm\) 0.02 & 2.73 \(\pm\) 0.01 & 2.78 \(\pm\) 0.02 & 2.74 \(\pm\) 0.01 \\
30 & 20 & 2.77 \(\pm\) 0.01 & 2.80 \(\pm\) 0.03 & 2.78 \(\pm\) 0.01 & 2.76 \(\pm\) 0.01 & 2.80 \(\pm\) 0.01 & 2.81 \(\pm\) 0.02 \\  & 30 & 2.86 \(\pm\) 0.02 & 2.74 \(\pm\) 0.01 & 2.80 \(\pm\) 0.01 & 2.77 \(\pm\) 0.01 & 2.78 \(\pm\) 0.01 & 2.73 \(\pm\) 0.01 \\  & 10 & 2.81 \(\pm\) 0.01 & 2.76 \(\pm\) 0.01 & 2.78 \(\pm\) 0.02 & 2.74 \(\pm\) 0.01 & 2.79 \(\pm\) 0.01 & 2.75 \(\pm\) 0.02 \\
40 & 20 & 2.76 \(\pm\) 0.02 & 2.75 \(\pm\) 0.02 & 2.76 \(\pm\) 0.01 & 2.72 \(\pm\) 0.01 & 2.77 \(\pm\) 0.01 & 2.77 \(\pm\) 0.01 \\  & 30 & 2.81 \(\pm\) 0.01 & 2.74 \(\pm\) 0.01 & 2.77 \(\pm\) 0.01 & 2.78 \(\pm\) 0.01 & 2.80 \(\pm\) 0.02 & 2.78 \(\pm\) 0.01 \\ \hline \hline \end{tabular} Data expressed as mean \(\pm\) standard deviation of three repetitions. No statistically significant differences were found between the treatments.  
\end{table}
Table 1: Changes in pH during storage at 4 \({}^{\circ}\)C of _Passiflora edulis_ f. _edulis_ Sims (_gulupa_) pulp subjected to low-frequency ultrasound treatments.