Table 2.
Solvents and methods reported in literature for the extraction of phenolic compounds from oregano.
| Solvent | Extraction Method/Parameters | Measured Parameters | Main Results | Reference |
|---|---|---|---|---|
| Ethanol, Supercritical CO2 (Ethanol as modifier) |
Focused UAE (20 kHz, 10 min) SFE (CO2 flow: 1–2 mL/min, T: 35–60 °C, P: 100–170 atm, ethanol 5–40%) |
TPC TEAC (ABTS) |
Optimum conditions determined by experimental design: Focused UAE (50% amplitude, 12.5 min) SFE (CO2 flow: 1 mL/min, T: 40 °C, P: 100 atm, 40% ethanol) TPC almost twice extracted by means of the Focused UAE. |
[85] |
| Supercritical CO2 (Ethanol as modifier) |
SFE (40–60 °C, 150–350 atm, fractionation of EO and phenolic compounds) |
HPLC DPPH β-carotene-linoleic acid |
Extraction yield increased with ethanol. Higher antioxidant capacity at 40 °C, 250 atm. Dihydroquercetin only extracted with ethanol as modifier. |
[86] |
| Water | ASE (25, 50, 100, 150, 200 °C, 103 atm, 30 min-individual extractions, or sequential extractions for 15 min at each temperature) |
TPC DPPH HPLC |
Extraction yield was higher at individual extractions, and increased with temperature. TPC of the extracts was not affected by temperature, but antioxidant activity Increased. |
[84] |
| Ethanol in water (0–96%) (s/l 1/40–1/20, w/v) |
CSE Temperature (22–60 °C), particle size (<315–1000 μm) |
TPC DPPH HPLC |
Optimum conditions: 60% ethanol, s/l 1/20, 22 °C, 600 μm. Increase of ethanol up to 60% increased RA and lithospermic acid yield. |
[64] |
| Methanol in water (70–90%) (s/l 1/20–1/5, w/v) |
CSE (Extraction time 4, 10, 16 h, particle size 20, 65, 110 μm) |
TPC DPPH |
All examined parameters were significant. Optimum conditions (RSM): MeOH (70%), s/l 1/20, time 16 h, particle size 20 μm TPC (18.75 mg/g dry herb) |
[78] |
| Methanol in water (32–80%) | Maceration (s/l 1/50, w/v, 80% methanol, overnight) ASE (66–200 °C, 103 atm) |
TPC FRAP HPLC |
Optimum ASE conditions (RSM): 33% methanol, 129 °C. TPC and FRAP at optimum ASE conditions were higher than those obtained by maceration. RA and luteolin-7-O-glucoside showed a decrease at T ≥ 150 °C in comparison to optimum ASE. |
[30] |
| Ethanol in water 90%, v/v s/l 1/100 Ethanol in propylene glycol (10–30%) Ethanol in glycerol (1–20%) |
CSE (25 °C, 24 h) Heat-reflux (95 °C, 1–6 h) Maceration (s/l 1/100, 24 h or 1/5, 48 h) Percolation (25 °C, 48 h) UAE (Ethanol 30–96%, s/l 1/20, 25–60 °C, 10 min) |
RA UA OA CAR |
Heat reflux and CSE gave the highest yields, while percolation the lowest. During heat reflux: Ethanol in non-aqueous solvents was more effective. Highest RA: Heat reflux (Ethanol, 90% v/v, 6 h) Highest OA, UA: Maceration (Ethanol, 90% v/v, 1/5, 48 h) Highest CAR: UAE (Ethanol, 96% v/v, 25 °C) or Continuous stirring |
[65] |
| Methanol in water 80% v/v Water |
CSE (25 °C, 60 min, 150 rpm) Infusion (5 min) Decoction (boiling in water, 5 min) |
HPLC DPPH β-carotene-linoleic acid lipid peroxidation |
CSE extracts showed higher antimicrobial activity. Higher TPC, flavonoids and antioxidant capacity by decostion > infusion > CSE | [69] |
| Water, Ethanol, Acetone, Ethyl acetate, Diethyl ether | Maceration (Three times, 25 °C, 24 h) |
TPC Flavonoids Condensed tannins DPPH |
Highest TPC: water Highest flavonoids: Diethyl ether Highest Condensed tannins: Diethyl ether Highest antioxidant capacity: Ethanol |
[70] |
| Methanol in water 70%, v/v Water |
UAE (bath) (T < 30 °C, 20 min) |
DPPH FRAP ABTS HPLC |
Hydroalcoholic extract contained higher RA, CAR and TPC. | [79] |
| Methanol in water 80%, v/v | UAE (12.5 kHz, 30 min) |
TPC HPLC ORAC |
There is a correlation between ORAC and TPC, but not between ORAC and RA. | [80] |
| Water (s/l 1/100, w/v) |
Infusion (85 °C, 15 min) Infusion (25 °C, 15 min) UAE (35 MHz, 25 °C, 15 min) |
TPC ABTS DPPH |
Hot water showed the highest efficiency for oregano and lemon balm. Lemon balm had higher TPC than oregano | [87] |
ABTS: 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical, ASE: accelerated solvent extraction, CAR: carvacrol, CSE: conventional solvent extraction, DPPH: 1,1-diphenyl-2-picrylhydrazyl radical, FRAP: ferric reducing antioxidant power, OA: oleanolic acid, RA: rosmarinic acid, SFE: supercritical fluid extraction, TEAC: trolox equivalent antioxidant capacity, TPC: total phenolic content, UA: ursolic acid, UAE: ultrasound assisted extraction.