Table 1.
Concentration (mg/g DW) of the main phenolic compounds identified in olive leaf extracts obtained by Soxhlet and MAE 10-80 (microwave-assisted extraction at 80 °C for 10 min) with different solvents analyzed by HPLC. Chromatograms are available in Figure S3.
| Extraction Method | Solvent | Phenolic Compounds | |||||||
|---|---|---|---|---|---|---|---|---|---|
| HY | VE | LU-7 | OL | LU | AP | AP-7 | Total | ||
| Soxhlet | Water | 4.68 ± 0.14 a | 1.48 ± 0.18 a | Traces | 6.95 ± 0.07 a | 0.02 ± 0.00 a | 0.50 ± 0.06 a | Traces | 13.99 ± 0.50 a |
| 50% EtOH | 8.04 ± 0.32 b | 0.71 ± 0.08 b | 1.55 ± 0.16 a | 18.44 ± 0.92 b | 1.55 ± 0.15 b | 0.44 ± 0.03 a,b | Traces | 30.74 ± 1.66 b | |
| 75% EtOH | 5.13 ±0.11 a | 0.54 ± 0.02 b | 1.83 ± 0.13 b | 27.13 ± 2.22 c | 1.79 ± 0.08 c | 0.45 ± 0.14 a,b | Traces | 37.22 ± 2.83 c | |
| 5% Gly | 1.67 ± 0.13 c | 0.65 ± 0.08 b | 0.53 ± 0.11 c | 1.05 ± 0.27 d | 0.50 ± 0.02 d | 0.27 ± 0.05 b | Traces | 4.82 ± 0.71 d | |
| 10% Gly | 5.97 ± 0.32d | 0.16 ± 0.06 c | Traces | 9.74 ± 0.68 a | 0.08 ± 0.00 a | 0.04 ± 0.00 c | Traces | 15.99 ± 1.06 a | |
| 15% Gly | 0.50 ± 0.06 e | 0.12 ± 0.00 c | Traces | 8.67 ± 0.86 a | 0.02 ± 0.00 a | 0.003 ± 0.00 c | Traces | 9.35 ± 0.92 e | |
| MAE 10-80 | Water | 4.06 ± 0.02 a | 0.56 ± 0.01 a | Traces | 12.84 ± 0.07 a | Traces | Traces | Traces | 18.60 ± 0.10 a |
| 50% EtOH | 2.28 ± 0.01 b | 1.27 ± 0.01 b | 0.51 ± 0.00 a | 40.49 ± 0.43 b | 1.02 ± 0.01 a | 0.38 ± 0.01 a | Traces | 48.52 ± 0.50 b | |
| 75% EtOH | 1.91 ± 0.01 c | 1.06 ± 0.01 c | 0.52 ± 0.00 b | 38.92 ± 0.71 b | 0.67 ± 0.01 b | 0.25 ± 0.01 b | Traces | 44.05 ± 0.75 c | |
| 5% Gly | 1.40 ± 0.01 d | 0.48 ± 0.00 d | Traces | 12.19 ± 0.01 a | 0.21 ± 0.00 c | Traces | Traces | 15.44 ± 0.03 d | |
| 10% Gly | 2.87 ± 0.02 e | 0.97 ± 0.01 e | Traces | 27.80 ± 1.69 c | 0.58 ± 0.00 d | 0.29 ± 0.01 c | Traces | 34.97 ± 1.74 e | |
| 15% Gly | 1.51 ± 0.01 f | 0.69 ± 0.00 f | 0.16 ± 0.00 c | 21,76 ± 1.65 d | 0.32 ± 0.00 e | 0.16 ± 0.01 d | Traces | 25.63 ± 1.68 f | |
Values are expressed as mean ± standard deviation. A standard deviation value of ‘0.00’ indicates values between 0.0001 and 0.0039. Within each extraction method, different superscript letters in the same column indicate values significantly different (p < 0.05) according to Tukey’s Multiple Range Test. Abbreviations: HY, hydroxytyrosol; VE, verbascoside; LU-7, luteolin-7-O-glucoside; OL, oleuropein; LU, luteolin; AP, apigenin; AP-7, apigenin-7-O-glucoside; Total, sum of individuals. Traces: under LOD (limit of detection).