# Effect of Extraction Method and Thermosonication on Apple Juice Quality
## 3 Results and Discussion
### Total Phenolic and Flavonoid Content  
Figures 3 and 4 present the influence of various treatment methods on the polyphenol and flavonoid content in apple juice. Pasteurization did not influence the polyphenol content in comparison to control sample. In the case of samples subjected to the action of ultrasound, a statistically significant increase in the value of the tested parameter was observed. This change relative to control amounted to 16% for treatment U1 (17.5 W cm\({}^{-2}\)) and 36% for treatment U2 (25 W cm\({}^{-2}\)). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Kind of Juice**} & \multicolumn{5}{c}{**Storage Time (h)**} \\ \cline{2-6}  & **24** & **72** & **120** & **168** & **216** \\ \hline Untreated C & 80 \(\pm\) 6a & ngf & nqf & nqf & nqf \\ \hline Sonicated U1 & 0 \(\pm\) 0b & \(<\)10 & nqf & nqf & nqf \\ \hline Sonicated U2 & 0 \(\pm\) 0b & 0 \(\pm\) 0b & nqf & nqf & nqf \\ \hline Pasteurized P & 0 \(\pm\) 0b & 0 \(\pm\) 0b & 0 \(\pm\) 0b & 0 \(\pm\) 0b & 0 \(\pm\) 0b \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Total number of mesophilic microorganisms (cfu/mL) in apple juice from piston press after ultrasound treatment stored at 20 \({}^{\circ}\)C. Different letters in the same column indicate values significantly different at P \(<\) 0.05. Figure 3: Effect of preservation method on total phenolic content in apple juice. Error bars represent standard deviations. Values that share the same letter are not significantly different at P \(<\) 0.05. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Kind of Juice**} & \multicolumn{5}{c}{**Storage Time (h)**} \\ \cline{2-5}  & **24** & **72** & **120** & **168** & **216** \\ \hline Untreated C & 70 \(\pm\) 5a & 80 \(\pm\) 6a & nqf & nqf & nqf \\ \hline Sonicated U1 & 0 \(\pm\) 0b & 0 \(\pm\) 0b & nqf & nqf & nqf \\ \hline Sonicated U2 & 0 \(\pm\) 0b & 0 \(\pm\) 0b & \(<\)10 & 13 \(\pm\) 4a & nqf \\ \hline Pasteurized P & 0 \(\pm\) 0b & 0 \(\pm\) 0b & 0 \(\pm\) 0b & 0 \(\pm\) 0b & 0 \(\pm\) 0b \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Total number of mesophilic microorganisms (cfu/mL) in apple juice from piston press after ultrasound treatment stored at 4 \({}^{\circ}\)C. Different letters in the same column indicate values significantly different at P \(<\) 0.05. A similar tendency was seen for flavonoid content. Pasteurization did not result in changed flavonoid content in juice, but treatments U1 and U2 resulted in a statistically significant increase of flavonoid content. Increased flavonoid content in juice was observed after ultrasound treatment, from 28.04 to 31.74 mg CAE/100 mL. The flavonoid content in the control sample was 25.30 mg CAE/100 mL. The obtained results are in line with data obtained by other authors. [PERSON] et al. [45] observed increased polyphenol and flavonoid content during ultrasound treatment of lime juice. [PERSON] et al. [46] obtained higher content of tested substances during sonication of apple juice (cv. Fuji). Several theories arose, aiming to explain the possible cause of the higher amount of polyphenol compounds in juices processed with ultrasound. The first theory speaks to the formation of hydroxyl radicals due to the effect of ultrasound followed by their bonding with aromatic rings of phenolic compounds. The addition of a second hydroxyl group in the ortho- or para-position has been reported to enhance the antioxidant activity of phenolic compounds [47]. Another explanation is the change of polyphenol oxidase (PPO) activity post-sonication treatment [45]. The third theory explaining the cause of increased polyphenol content is that cell walls of solids in juice are disrupted due to cavitation. This process leads to the release of certain chemically bound polyphenols, resulting in their increased availability. In our opinion, the latter mechanism is the most likely and influences, to the greatest degree, the increased polyphenols detected in ultrasound-processed juice.