Table 6.
Techniques and main results reported in literature for the extraction of phenolic compounds from St. John’s wort.
| Extraction Method and Parameters | Analysis | Main Results | Reference |
|---|---|---|---|
| CSE (1 g/25 mL under stirring) Phase I: Water, ethanol 50% in water, ethanol, ethanol 50% in acetone, acetone, chloroform, hexane Phase II: ethanol in acetone 20–80%, 23–55 °C, 4.5–7.5 h |
HPLC | Phase I: ethanol, ethanol 50% in acetone, and acetone were more effective for most compounds. Chloroform and hexane extracted only one compound, possibly hyperforin. Best extraction time 4–8 h. Phase II: experimental design and RSM showed optimum yield for all components 44–59% ethanol in acetone, 5.3–5.9 h, and 55 °C, except hypericin that showed maximum yield at 23 and 40 °C. |
[172] |
| CSE (1g/30 mL, 4 °C, 60 min, under stirring and dark) Ethanol, acetonitrile, ethyl acetate, chloroform, methyl-tert-butylether, petroleum ether, hexane |
HPLC (hyperforin) |
All solvents presented close yields (3.2–2.8 mg/g dry plant), except ethanol that presented the lowest (1.9 mg/g dry plant). Hexane and petroleum ether presented the highest purity (hyperforin content) in the extracts. | [164] |
| SFE (311, 380, and 449 atm, 40, 50, and 60 °C). | HPLC (hyperforin) |
The optimum conditions were 380 atm, 50 °C, static extraction 10 min followed by dynamic extraction 90 min at CO2 flow rate 1 mL/min. Extraction was not quantitative (about 60% of hyperforins were extracted). Addition of methanol did not increase yield, while decreased purity of the extract. |
[163] |
| SFE | HPLC (hyperforin) |
High extraction efficiency when CO2 density > 0.60 g/mL. Mild conditions (30 °C, 80 atm, density-0.64 g/mL) gave the best yield (12 mg/g dry plant) that was comparable to UAE or CSE at boiling temperature | [171] |
| SFE (100, 150, 200 atm, 40, 50 °C, various CO2 densities) UAE (methanol) |
HPLC (hyperforins) |
The lower the CO2 density (low pressure, high temperature) the lower the hyperforins yield and purity of the extracts. 200 atm and 313 K gave the best results. Hypericins were not extracted. Pretreatment with SFE (100 atm, 313 K) increased the yield of UAE extraction. |
[170] |
| SFE (250 and 300 atm, 40 °C or 300 atm 50 °C, with or without 10% ethanol as co-solvent) Subcritical CO2 (70 atm, 22 °C) |
HPLC (hypericin hyperforin, flavonoids) |
Hyperforin was easily extracted, while hypericin and flavonoids were not extracted even with ethanol. The yield increased sharply under SFE and slower with liquid CO2. Liquid CO2 gave the highest hyperforin yield and purity of the extract. Ethanol increased hyperforin yield but decreased purity of the extract. |
[169] |
| Soxhlet (20 g/200 mL) Ethanol, 2-propanol, ethyl acetate, hexane SFE (40 °C, 450 atm, flow rate 7 kg CO2/(h kg herb) |
UV–vis (hypericin) HPLC (hypericin hyperforin) |
Highest hypericin yield with ethanol, very low with 2-propanol and ethyl acetate, not detected in hexane and supercritical CO2. Hyperforin yield: supercritical CO2 >> Soxhlet with 2-propanol > ethanol > ethyl acetate, fully degrader in hexane due to long extraction time. |
[166] |
| Soxhlet (5 g/100 mL) methanol 6 h successive with diethyl ether 4 h, and ethanol 6h UAE (bath, 1 g, 75 mL, 0.5 h, 2 repeated extractions) methanol successive with petroleum ether, chloroform, ethyl acetate, methanol Digestion (1 g with 100 mL hot methanol) Maceration a) 1 g/100 mL methanol, under stirring, 2 h) b) 1 g/150 mL acetone 90% in water, under stirring, 0.5 h, 2 repeated extractions) |
UV–vis (hypericin) HPLC |
Only Soxhlet b, and maceration b gave extracts free from chlorophyll pigments. Soxhlet b gave mainly hyperforin in diethyl ether and hypericins in ethanol. Hyperforin was favored by lower temperature (UAE a, compared to Soxhlet a) and non-polar solvents (petroleum ether in UAE b). Flavonoids were favored by higher temperature (Soxhlet a and digestion, compared to UAE a and maceration a). The best extraction procedure to obtain a representative extract with all metabolites is UAE with methanol or ethanol. |
[157] |
| Soxhlet (5 g/150 mL methanol 24 h) UAE (5 g/100 mL methanol, 5–60 min) Direct (20 kHz, 40 or 60 W) Indirect (35 kHz) Maceration (5 g/100 mL methanol 24 h) ASE (methanol, 40 °C, 100 atm) |
HPLC | Direct UAE showed the best yields for all compounds that increased with power (60 W). 20 min were efficient for all compounds, except hyperforin that needed 5 min. Yields obtained by the rest methods followed the order Soxhlet ≥ ASE ≥ indirect UAE > maceration. |
[158] |
| Soxhlet (1 g/200 mL methanol, 1–48 h) UAE (bath, 1 g/22 mL methanol, 60 °C, 30–120 min) ASE (22–200 °C, 152 atm, 5 min heating, 5 min static time, 3-cycle extraction) Methanol, tetrahydrofuran, acetone, methylene chloride, hexane |
HPLC (hyperforin was not quantitated) |
Maximum yield in Soxhlet obtained at 8 h. Increase of time in UAE increased components yields. 3–6 repeated ASE were necessary for the recovery of 99% of each component. All solvents were tested at 22 °C, methanol or tetrahydrofuran were more effective for the extraction of phenolic acids and flavonoids, acetone was more effective for the extraction of the non-polar hypericins, while methylene chloride and hexane were ineffective. The effect of temperature was studied with ethanol. Yield increased with temperature up to 150 °C and decreased afterwards, except quercetin that was degraded even at 150 °C For more polar compounds yield followed the order Soxhlet (24 h) > UAE (60 °C, 2 h) > ASE (60 °C, 0.5 h). |
[161] |
| Heating under reflux (solvent boiling point, 90 min) UAE (25 °C, 30 min) MAE (75 °C, 30 min) ASE (120 °C, 100–150 atm, 20 min) All methods with 70% methanol in water, solid/liquid 1/50 |
HPLC | Yield of all compounds followed the order ASE > MAE > heating under reflux > UAE. Heating under reflux at solid/liquid 1/100 presented yields comparable to ASE. |
[160] |
| UAE (0.5 g/30 mL, bath 40 kHz) methanol in water 20–80%, HCl 0.8–2.0 M, 30–70 °C, 20–80 min | HPLC (flavonoids and phenolic acids) TPC, ABTS+ |
BBD and analysis of results indicated all parameters significant. Optimization was based on quercetin yield that increased with methanol concentration and temperature, while it was not affected by HCl concentration at higher temperature. Cyanidin, kaempferol, and protocatechuic acid were also found in the extract. | [176] |
| CSE (1 g/50 mL under stirring) Water Glycerol in water 10% 50–70 °C, 5–95 min |
HPLC (phenolic compounds) TPC, FRAP |
Aqueous glycerol (10%) increased the extraction rate, compared to water, the phenolic compound yield (90 mg GAE/g dry herb, versus 78 mg GAE/g dry herb for water), and the ferric reducing power (by 9%). Phenolic acids, quercetin glycosides, and catechin were the major extracted components, while hypericin was detected. CCD and RSM revealed 70 °C and 69 min as optimum conditions. | [177] |
ABTS: 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical, ASE: accelerated solvent extraction, CSE: conventional solvent extraction, FRAP: ferric reducing antioxidant power, MAE: microwave assisted extraction, SFE: supercritical fluid extraction, TPC: total phenolic content, UAE: ultrasound assisted extraction.