## 3 Results and Discussion
### Identification of Phenolic Extracts  
The liquid chromatography-mass spectrometry (LC-MS) technique is widely used in the structural characterization of the phenolic compounds in WOF [17; 31; 59]. In the current study, the identification of the phenolic compounds in the WOF extract was performed by LC-MS-ESI in negative ionization mode, accompanied by a DAD detector. A representative UV chromatogram at 280 nm of phenolic compounds in the WOP extract is illustrated in Figure 2. A total of 18 major phenolic compounds were successfully identified in the WOF extract, which include seciridoids (10), flavonoids (3), simple phenols (3), and organic acids (2), as listed in Table 3. The phenolic compounds were tentatively identified and characterized based on their retention times, UV spectra, and MS spectra ([M-H]\({}^{-}\) ions), as confirmed by using commercial standards. However, secoiridoid derivatives (peaks 5, 7, 8, 12, 13, 15, 16, and 18) were identified based on the literature information concerning olive fruit characterization, due to the limitation of available standards [17; 30; 60; 61; 62; 63; 64]. Figure 1: Total phenolic contents in wild olive fruit extracts obtained by ultrasound-assisted extraction (UAE) using different extraction solvents. Means followed by the same letter within a column are not significantly different (\(p>0.05\)). Secoiridoids were the major category of phenolic compounds identified in the WOF phenolic extract, belonging to oleuropein derivatives (peaks 8 and 18), ligstroside derivatives (peaks 12 and 16), oleoside-type (5 and 13), and phenolic acid derivatives (peak 7). Oleuropein was the major peak identified, showing a pseudo-molecular ion [M-H]\({}^{-}\) at \(m/z\) 539 (peak 14) (Figure 1). Peaks 5 and 13 presented a similar profile with maximum absorbance at \(\sim\)280 nm and the same molecular ion [M-H]\({}^{-}\) at \(m/z\) 389, and were characterized as oleoside/secologanoside isomers (A and B), according to the literature data [17; 60]. Other related compounds with the same UV max at \(\sim\)280 nm were phenolic acid glucose (peak 7) with \(m/z\) 403, oleuropein aglycone isomers (peaks 8 and 18) with \(m/z\) 377, \begin{table}
\begin{tabular}{c c c c c c} \hline
**Peak** & **Rt (min)** & **UV (nm)** & **[M-H]\({}^{-}\)** & **Compound** & **Family** & **Reference** \\ \hline
1 & 2.96 & 280 & 191 & **quinic acid** & organic acid & standard solution \\
2 & 3.68 & 280 & 191 & **citric acid** & organic acid & standard solution \\
3 & 3.86 & 278 & 315 (153) & **hydroxy tyrosol glucoside** & simple phenols & [17; 60; 64] \\
4 & 4.81 & 281 & 153 & **hydroxytyrosineol** & simple phenols & standard solution \\
5 & 5.00 & 282 & 389 & **oleoside/secologanoside (A)** & secoiridoid & [17; 60; 61] \\
6 & 6.03 & 278 & 137 & **tyrosineol** & simple phenols & solution \\
7 & 7.02 & 240, 280 & 403 & **elenolic acid glucoside** & secoiridoid & [61; 62] \\
8 & 7.52 & 283, 321 & 377 & **oleuropein aglycone (A)** & secoiridoid & [30; 60; 61] \\
9 & 9.02 & 290, 353 & 609 & **rutin** & flavonoid & standard solution \\
10 & 9.71 & 290, 336 & 623 & **verboseoside** & secoiridoid & standard solution \\
11 & 9.92 & 250, 345 & 447 & **luteolin-7-glucoside** & flavonoid & standard solution \\
12 & 10.72 & 237, 280 & 509 & **dimethyl ligstroside** & secoiridoid & [60] \\
13 & 11.41 & 278 & 389 & **oleoside/secologanoside (B)** & secoiridoid & [60; 61] \\
14 & 12.68 & 281 & 539 & **oleuropein** & secoiridoid & standard solution \\
15 & 14.00 & 282 & 583 (537) & **lucidumoside C** & secoiridoid & [61] \\
16 & 14.50 & 238, 278 & 523 (377) & **ligstroside** & secoiridoid & [17; 60] \\
17 & 15.21 & 253, 366 & 285 & **luteolin** & flavonoid & standard solution \\
18 & 15.81 & 283, 321 & 377 (307) & **oleuropein aglycone (B)** & secoiridoid & [30; 60; 61] \\ \hline \end{tabular}
\end{table} 
Table 3: List of tentative major phenolic compounds identified by LC-DAD-MS in the WOF extracts.