Table 2.
Optimization of key parameters for phenol pressurized liquid extraction (PLE). All extractions were performed at 80 °C temperature and at 100 bar pressure. The solid/liquid column indicates the kgDW of used pomace in for 1 L of solvent; the liquid/solid column indicates the amount of solvent for 1 kgDW of pomace. Total phenol quantification results of each extract were expressed as g of gallic acid (GA) equivalent per kg of pomace dry weight (gGAeq/kgDW) and as g of GA equivalent per litre of extract (gGAeq/L). Different letters indicate statistically significant difference (one-way ANOVA followed by post hoc two-tailed Student’s t-test, p < 0.05) among data expressed in the same measure unit. The extended sample code indicates the type of pre-treatment, the extraction time and the mobile phase composition. Data are the mean ± SD (n = 2). EtOH-H2O, 50% ethanol/water mixture; PWC, wet coarse milled pomace; PWF, wet fine milled pomace; PDD, defatted dried coarse milled pomace; PD, dried coarse milled pomace.
| Sample (Extended sample code) | Solid/liquid (kgDW/L) | Liquid/solid (L/kgDW) | Pre-treatment | Time (min) | EtOH-H2O /CO2 ratio | Total phenols |
|
|---|---|---|---|---|---|---|---|
| gGAeq/kgDW | gGAeq/L | ||||||
| T30 (PWC-T30-S75) | 0.023 | 43.41 ± 6.67 | PWC | 30 | 75% | 61.91 ± 6.51 a | 1.44 ± 0.07 a |
| T40 (PWC-T40-S75) | 0.016 | 63.47 ± 5.67 | PWC | 40 | 75% | 70.67 ± 3.86 b | 1.13 ± 0.04 b |
| T50 (PWC-T50-S75) | 0.012 | 83.21 ± 5.34 | PWC | 50 | 75% | 78.85 ± 7.33 b | 0.94 ± 0.02 b |
| S50 (PWC-T30-S50) | 0.051 | 19.48 ± 0.00 | PWC | 30 | 50% | 48.46 ± 11.42 a,c | 2.47 ± 0.58 a,c |
| S100 (PWC-T30-S100) | 0.019 | 52.75 ± 5.71 | PWC | 30 | 100% | 67.72 ± 5.37 a,b | 1.31 ± 0.04 a,b |
| PWF (PWF-T30-S75) | 0.028 | 35.12 ± 0.11 | PWF | 30 | 75% | 70.55 ± 0.61 b | 2.01 ± 0.07 b |
| PD (PD-T30-S75) | 0.028 | 35.96 ± 0.52 | PD | 30 | 75% | 72.18 ± 7.33 a,b | 2.30 ± 0.41 a,b |
| PDD (PDD-T30-S75) | 0.027 | 37.04 ± 0.22 | PDD | 30 | 75% | 67.36 ± 2.21 a,b | 1.76 ± 0.06 a,b |