## 2 Results and Discussion
### Determination of Phenolic Compounds  
Each mill produced several batches of oils both with and without applying the SHE (Table 1). After evaluation of oil yields, the phenolic and volatile fractions of samples were analyzed and the sensorial characteristics were evaluated by expert panelists (data not shown), to confirm they belonged to the extra virgin category. These analyses were selected for defining the final quality of the produced oils. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**n\({}^{\circ}\)** & **Sample** & **Cultivar** & **Olive Mill** & **Crusher** & **MI** & \
\begin{tabular}{c} **\% of Fruit Oil** \\ **Content in** \\ **the Fresh Matter** \\ \end{tabular} &
\begin{tabular}{c} **\% of Pomace Oil** \\ **Content in** \\ **the Fresh Matter** \\ \end{tabular} \\ \hline
1 & OM-N & Coratina & Mimi &
\begin{tabular}{c} Hammer \\ Crusher \\ \end{tabular} & 1 & 19.6 = 0.6 & 7.5 = 0.5 \\ \hline
2 & OM-U & Coratina & Mimi &
\begin{tabular}{c} Hammer \\ Crusher \\ \end{tabular} & 1 & 19.6 = 0.6 & 2.0 = 0.6 \\ \hline
3 & 1N & Peranzana & & & & & \\
4 & 3N & Peranzana & & & & & \\
5 & 5N & Peranzana & & & & & \\
6 & 9N & Peranzana & & & & & \\
7 & 10N & Peranzana & & & & & \\
8 & 12N & Peranzana & & & & & \\ \hline
9 & 2U & Peranzana & & & & & \\
10 & 4U & Peranzana & & & & & \\
11 & 6U & Peranzana & & & & & \\
12 & 7U & Peranzana & & & & & \\
13 & 8U & Peranzana & & & & & \\
14 & 11U & Peranzana & & & & & \\ \hline
15 & P5N & Coratina/Ogliarola & & & & & \\
16 & P6N & Coratina/Ogliarola & & & & Crusher & 4 & 21.0 = 0.4 & 1.8 = 0.4 \\ \hline
17 & P3U & Coratina/Ogliarola & & & & & \\
18 & P4U & Coratina/Ogliarola & & & & & \\
19 & P7U & Coratina/Ogliarola & & & & & \\ \hline
20 & C4N & Cellina di Nardó & & & & & \\ \hline
21 & C3U & Cellina di Nardó & & & & & \\
22 & C5U & Cellina di Nardó & & & & & \\
23 & C6U & Cellina di Nardó & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of the analyzed extra virgin olive oils (EVOOs) produced in the different mills with (U) and without (N) the use of ultrasounds. Oils from the same mill were produced on the same days. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Maturity** & **0** & **1** & **2** & **3** & **4** & **5** & **6** & **7** \\ \hline
1 & Skin color & Skin color with & Skin color with & & & & & & Skin color all \\  & & & -chall the fruit & -shalt the fruit & Skin color all & & & & & \\  & Skin color & Skin color & surface & surface & & purple or black & & & & \\  & deep green & yellow-green & turning red, & turning red, & with all white & & & & \\  & & purple, or & purple, or & or & green flesh & & & & & \\  & & black & black & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Maturity index (MI) classification groups of olives based on skin and flesh color. Figure 1: Ripening index according to the different color of the fruit. The total phenolic amount was determined according to the IOC method and then the sum of hydroxytyrosol and tyrosol was evaluated after acidic hydrolysis applying the validated method [23]. The values obtained before and after hydrolysis are compared in Figure 3A, while the mean values obtained for each group of oils from different mills are compared in Figure 3B. As expected, the richest variety in terms of phenolic compounds was Coratina (samples OMU and OMN) followed by the Coratina-Ogliarola blend (samples P6N and P7U), while the lowest values were obtained for oils derived by Cellina di Nardo (C3U, C6U, C5U, and C4N). Overall, the values of total phenols varied in a wide range, showing concentrations from 58 mg/kg to 510 mg/kg. For fresh EVOOs, the amount of free hydroxytyrosol and tyrosol was negligible in most of the samples, while an average concentration of 14.5 mg/kg was observed only for samples from Coratina and the Coratina-Ogliarola blend (data not shown).