Table 1.
Extraction technologies to obtain bioactive compounds from pomegranate peels, as well as the analytical techniques reported for their identification.
| Technology | Extraction Conditions | Identification Method | Outcomes | Reference |
|---|---|---|---|---|
| SLE | Methanol: water (4:1, v/v) for 3 days at room temperature, LSR of 5:1 (mL/g) | HPLC-PDA | TPC: 188.9 mg GAE/g dw; TFC: 13.95 mg QE/g dw Identification of 23 phenolic compounds and 20 flavonoids |
[43] |
| CPE | For total phenols: 8.22% Triton X-114, 4% NaCl at 36.80 °C and pH 4 For flavonoids: 8.27% Triton X-114, 4.06% NaCl at 34.30 °C and pH 5.07 |
Not indicated | TPC: 205.2 mg of GAE/g; TFC: 60.05 mg of QE/g | [59] |
| SLE, IR and UAE | Solvents: water, 50% ethanol and 8 different DES. The temperature for the three technologies was fixed at 50 °C | HPLC-DAD | The combination of DES and IR leads to the highest yield of polyphenols (152 mg/g) with high antioxidant activity and good antimicrobial properties. Identification of caffeic acid, kaempferol, luteolin, protocatechuic acid, ellagic acid, chlorogenic acid, hydroxybenzoic acid, gallic acid and quercetin |
[60] |
| MAE and UAE | For MAE: 50% aqueous ethanol; LSR: 60:1 mL/g; power, 600 W for 4 min For UAE: water, LSR: 32.2:1 mL/g, amplitude level: 39.8%, pulse duration/pulse interval ratio, 1.2/1 at 34.7 °C for 10 min |
HPLC-UV–vis | TPC (MAE): 199.4 mg GAE/g; TPC (UAE): 119.82 mg GAE/g. Identification and quantification of punicalagin: 143.64 mg/g for MAE and 138.8 mg/g for UAE |
[25] |
| MASE | TPC: 600 W, 24% ethanol for 35 min; TFC: 800 W, 30% ethanol for 25 min; TTC: 800 W, 30% ethanol for 15 min | UHPLC/ESI/MS | TPC: 373 mg GAE/g; TFC: 155 mg RE/g; TTC: 317 mg GAE/g. Identification of 13 phenolic compounds, mainly ellagitannins and granatin |
[61] |
| PUAE | Intensity level: 105 W/cm2; duty cycle: 50% for 10 min | HPLC-UV-DAD | Punicalagin: 146.58 mg/g; ellagic acid: 20.66 mg/g; gallic acid: 0.053 mg/g | [62] |
| UAE | Ultrasonic amplitude 60% for 6.2 min | Not indicated | Yield: 13.1%; TPC: 42.2 mg GAE/g; DPPH: 88%; FRAP: 1824.6 μmol Fe2+/g; IC50: 0.51 mg/mL | [23] |
| UAE | Ultrasonic power of 148 W, 55 °C for 63 min using LSR: 24 mL/g | Not indicated | Polysaccharide yield: 13.658% | [63] |
| HIFU | Choline chloride:acetic acid:water (1:1:10 M), amplitude of 60% for 11 min | HPLC-ESI-Q-TOF/MS | Protein: 20 mg/g. Identification of 23 different peptides and of 20 different phenolic compounds, mainly punicalin, punicalagin, galloyl-HHDPhexoside, ellagic acid-hexoside, and ellagic acid |
[29] |
| HPE | Depending on the variable evaluated, the conditions ranged between 356 and 600 MPa and 32–80% ethanol for 23–30 min | UHPLC-DAD/LC-DAD/ESI-MS | Yield: 31 mg/g; TPC: 52 mg GAE/g; TFC: 20 mg of QE/g; TTC: 2.02 mg of CAE/g; TAC: 86 mg cyd-3-glu/g; ABTS: 269 mg TE/g; DPPH: 314 mg TE/g; FRAP: 436 mg TE/g | [64] |
| HPE + EE | HPE conditions: 300 MPa for 15 min; EE: 4% pectinase and 4% cellulase for 15 min | HPLC-DAD-MSn | Total extraction yield: 41%; TPC: 207 mg GAE/g; DPPH: 334 mg TE/g Identification of quinic acid, a punicalin isomer, two bis-HHDP-glucoside isomers, 2-O-galloylpunicalagin, two punicalagin isomers, galloyl-HHDP-glucoside and digalloylpentoside |
[24] |
| EASCFE | EE: cocktail enzyme (mixture of cellulase, pectinase and protease; 50:25:25) at 3.8%, 49 °C, pH 6.7 for 85 min; SCFE: ethanol as co-solvent (2 g/min), 55 °C, 300 bar for 100–120 min | HPLC-DAD-ESI–MS | TPC: 301.53 mg GAE/g Identification of p-coumaric acid, vanillic acid, gallic acid, caffeic acid, ferulic acid, syringic acid, sinapic acid |
[30] |
TPC: total phenolic compounds; TFC: total flavonoid compounds; TTC: total tannin content; TAC: total anthocyanins content; GAE: gallic acid equivalents; QE: quercetin equivalents; RE: rutin equivalents; CAE: catechin equivalents; TE: Trolox equivalents; cyd-3-glu: cyanidin-3-glucoside equivalents; CPE: cloud point extraction; SLE: solid–liquid extraction; DES: deep eutectic solvents; MAE: microwave-assisted extraction; MASE: microwave-assisted soxhlet extraction; PUAE: pulsed ultrasound-assisted extraction; UAPLE: ultrasound and pressurized liquid extraction; HIFU: high intensity focused ultrasounds; HPE: high pressure extraction; EE: enzymatic extraction; EASCFE: enzyme-assisted supercritical fluid extraction.