Table 2.
Various sample preparation methods for the analysis of phenolics from common buckwheat sprouts
| Phenolicsa | Analytical sample preparationb | Purificationb | Analytical instrument c | References |
|---|---|---|---|---|
| Orientin, isoorientin, vitexin and rutin | 0.1 g sample + 1 mL 80% EtOH (3 h shaking) → centrifuged (10,000 g, 10 min) → supernatant was collected | UFLC | Lim et al. (2012) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin and Q-Gal-Rha | 0.05 g sample + 1 mL 60% MeOH containing 0.4% TFA → 0.5 min UAE and 0.5 min vortexed (2x) → centrifuged (5,000 g at 4 °C) → supernatant was collected → re-extraction of residue (5 × with same procedure) | HPLC–UV | Horbowicz et al. (2013) | |
| Orientin, isoorientin, vitexin, isovitexin and rutin |
(1) Analysis of rutin: sample + 50% acetone (2 h agitation) → suction filtration → evaporated → dried residue used (2) Analysis of other flavonoids: sample + 50% MeOH (2 h agitation) → centrifuged (10,000 rpm, 15 min) → supernatant was collected → re-extraction of residue (1 × with same procedure) → pooled supernatants were dried |
CEUV HPLC–UV HPLC–MS |
Koyama et al. (2013) | |
| Rutin | 200 mg sample + 40 mL 80% EtOH (16 h stirring, 40 °C) → centrifuged (8,000 g, 10 min) → filtered | HPLC–UV | Tsurunaga et al. (2013) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin, quercetin and chlorogenic acid | 10 mg sample + 1 mL MeOH containing 10% phosphoric acid → vortexed 5 min → incubated (3 h at 37 °C) → centrifuged (1,000 g, 5 min) and filtered | HPLC–UV | Arasu et al. (2014) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin, quercetin and chlorogenic acid | 10 mg sample + 1 mL MeOH containing 10% phosphoric acid → vortexed 5 min → incubated (3 h at 37 °C) → centrifuged (10,000 g, 5 min) and filtered | HPLC–UV | Kim et al. (2014b) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin, quercetin and chlorogenic acid | 10 mg sample + 1 mL MeOH containing 10% phosphoric acid → vortexed 5 min → incubated (3 h at 37 °C) with 0.5 min vortexing every 1 h → centrifuged (1,000 g, 5 min) and filtered | HPLC–UV | Lee et al. (2014) | |
| Rutin and quercetin | 1 g sample + 95% EtOH (1:20 w/v) → 6 h heating (70 °C) → vacuum filtered, dissolved in 95% EtOH, and stored (4 °C) | HPLC–UV | Ren and Sun (2014) | |
| Cy-Gal, Cy-Glu, Cy-Rut, Cy-Gal-Rha, orientin, isoorientin, vitexin, isovitexin, rutin, Q-Gal-Rha, Q-Glu, quercetin, epicatechin and procyanidin B2 | 0.05 g sample + 1 mL 60% MeOH containing 0.4% → TFA 0.5 min UAE and 0.5 min vortexed (2x) → centrifuged (13,200 g at 4 °C, 10 min) → supernatant was collected → re-extraction of residue (5 × with same procedure) → pooled supernatants were centrifuged (13,200 g at 4 °C, 20 min) |
HPLC–DAD HPLC–MS HPLC–CoulArray–ECD |
Wiczkowski et al. (2014) | |
| Cy-Gal, Cy-Glu, Cy-Gal-Rha, Cy-Glu-Rha, orientin, isoorientin, vitexin, isovitexin, rutin and Q-Gal-Rha | 0.05 g sample + 1 cm3 60% MeOH containing 0.4% TFA → 0.5 min UAE and 0.5 min vortexed (2x) → centrifuged (5,000 g at 4 °C, 5 min) → supernatant was collected → re-extraction of residue (5 × with same procedure) → pooled supernatants were centrifuged (5,000 g at 4 °C, 15 min) |
HPLC–DAD HPLC–MS |
Horbowicz et al. (2015) | |
| Orientin, isoorientin, vitexin, isovitexin, Q3R and rutin | 15 g sample + 150 mL 70% EtOH (48 h soaking) → filtered → re-extraction of residue (2 × with same procedure) → filtered solvent was pooled → evaporated → 840 mg obtained extract was dissolved with 40 mL water and 80 mL EtOAc/n-BuOH (3:1) → 250 mg EtOAc/n-BuOH fractionated extract was collected after separation and evaporation (2x) → suspended in 20 mL water and 40 mL EtOAc → aqueous fraction was collected and dried → 70 mg dried extract was obtained and stored (4 °C) |
HPLC–PDA HPLC–Q–TOF/MS |
Nam et al. (2015) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin, K3R, quercitrin, myricetin, luteolin, quercetin, kaempferol, gallic acid, DHBA, THBA, p-HBA, chlorogenic acid, vanillic acid, caffeic acid, syringic acid, p-coumaric acid, ferulic acid, sinapic acid and THCA | 3 g sample + 50 mL 70% MeOH (1 h UAE) → filtered and concentrated to 10 mL → filtered |
HPLC–UV HPLC–MS |
Zhang et al. (2015) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin, Q-Gal-Rha, Cy-Gal-Rha and Cy-Glu-Rha | Sample + 60% MeOH containing 0.4% TFA (1:4) | HPLC–UV | Dębski et al. (2016) | |
| Rutin | Sample + 50% MeOH → lyophilized → dissolved in 1 mL 10% aqueous acetonitrile with 0.1% formic acid | HPLC–UV | Nakamura et al. (2016) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin, apigenin, quercetin, luteolin, kaempferol, naringenin, gallic acid and caffeic acid | 10 g sample + 90 mL absolute MeOH → HAE (22,000 rpm; 2 × 30 s extraction, 10 s pause each round) → 3 min incubation → solvent/supernatant was filtered |
● Sorbent (100 mg Strata-X RP cartridges) ● 1st conditioning (3 mL absolute MeOH); 2nd conditioning (3 mL 10% MeOH) ● 30 mL diluted methanol extract (1:9 in water v/v) was loaded → washed with 3 mL 10% MeOH → dried with vacuum pump → elution (3 mL absolute MeOH) ● Eluted extract was evaporated, dissolved in 1 mL 50% MeOH (ultrasound and vortexing), and filtered |
HPLC–MS | Terpinc et al. (2016) |
| Derivatives of benzoic acid and cinnamic acid | 800 mg sample + 20 mL water (adjusted to pH 2; 6 M HCl) → 5 × extraction with 20 mL DEE → evaporated under vacuum → neutralized and lyophilized → residue was hydrolyzed in 20 mL 2 M NaOH (4 h, nitrogen atmosphere) → acidified to pH 2 (6 M HCl) → 5 × extraction with 30 mL DEE → 15 mL 6 M HCl was added, placed under nitrogen atmosphere → hydrolyzed in a boiling water bath (1 h) → 45 mL DEE was added → ether extracts were evaporated → dissolved in 10 mL methanol and filtered | HPLC–DAD | Wiczkowski et al. (2016) | |
| Orientin, isoorientin, vitexin and rutin | Sample + absolute MeOH (1:20 w/v) → extract was dissolved in EtOH | HPLC–UV | Yang et al. (2016) | |
| 4-HBA, catechin, chlorogenic acid, caffeic acid, epicatechin, rutin and quercetin | 0.1 g sample + 5 mL 80% MeOH containing 10% acetic acid → UAE (10 min at 28 °C) → water bath (1 h at 37 °C) → centrifugation (3,000 rpm, 10 min) → re-extraction of residue (1 × with same procedure) → pooled supernatant was dried using nitrogen gas → dissolved with 5 mL absolute MeOH → diluted, filtered and stored |
HPLC–UV HPLC–MS |
Park et al. (2017) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin and quercetin | Sample + 1 mL MeOH containing 10% phosphoric acid → vortexed 5 min → incubation (3 h at 37 °C) with vortexing every 1 h → centrifuged (1,000 g, 5 min) and filtered | HPLC | Jeong et al. (2018) | |
| Orientin, isoorientin, vitexin, isovitexin and rutin | 100 mg sample + 1 mL MeOH (overnight at −20 °C) → centrifuged (17,000 g, 10 min) and filtered | UPLC–MS | Koja et al. (2018) | |
| Orientin, isoorientin, vitexin, isovitexin, Q3R and rutin | 15 g sample + 150 mL absolute MeOH (48 h soaking) → 10 min HAE → solvent containing extract was filtered → re-extraction of residue (2 × with same procedure) → filtered solvent was pooled → evaporated and stored at −20 °C | HPLC–PDA | Nam et al. (2018a) | |
| Orientin, isoorientin, vitexin, isovitexin, Q3R and rutin | 15 g sample + 150 mL absolute MeOH (24 h soaking) → solvent containing extract was filtered → re-extraction of residue (2 × with same procedure) → filtered solvent was pooled → evaporated | HPLC–PDA | Nam et al. (2018b) | |
| Orientin, isoorientin, vitexin, isovitexin, Q3R and rutin | Sample + 90% MeOH (30 min UAE) → centrifuged (2,232 g, 10 min) and filtered → re-extraction of residue (1 × with same procedure) → filtered supernatant was pooled → filtrate/supernatant was evaporated and stored at −50 °C | HPLC–PDA | Jang et al. (2019) | |
| Orientin, isoorientin, vitexin, isovitexin, Q3R and rutin |
● Ultrasound-assisted DES-based extraction technique ● Optimum: 80% CCTG, extraction temperature of 56 °C, extraction time of 40 min ● Sample:solvent (100 mg:1 mL) ● Extract was centrifuged (10,000 rpm, 30 min) → supernatant was filtered |
● Column containing sorbent (Sep-Pak C18 cartridges) ● 1st conditioning (2 × 5 mL absolute MeOH); 2nd conditioning (2 × 5 mL 0.01 N aqueous HCl) → evaporation ● Extract (0.5 mL) was loaded to column ● 1st elution with 6 mL 0.01 N aqueous HCl ● 2nd elution with 2 × 4 mL absolute MeOH ● Evaporated extract was dissolved (10 mL) with absolute MeOH |
HPLC–PDA HPLC–Q–TOF/MS |
Mansur et al. (2019) |
| Benzoic acid, caffeic acid, catechin, chlorogenic acid, epicatechin, gallic acid and rutin | 0.2 g sample + 2 mL 80% MeOH → vortexed 0.5 min → UAE (1 h at 37 °C) → centrifuged (16,000 g, 15 min) → re-extraction of residue (1 × with same procedure) → pooled supernatant was evaporated → dissolved with 2 mL absolute MeOH and filtered | HPLC–UV | Park et al. (2019) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin and quercetin | 1 g sample + 15 mL 70% EtOH (1 h UAE) → filtered | UPLC–MS | Chen et al. (2020) | |
| Orientin, isoorientin, vitexin, isovitexin, Q3R and rutin |
● MSPD-based extraction ● Optimum: C18 sorbent/sample (2:1; 100 mg) and 10 min static extraction with 5 mL 80% EtOH ● Extract was filtered |
HPLC–PDA | Mansur et al. (2020) | |
| Orientin, isoorientin, vitexin, isovitexin, rutin and quercetin | Sample + 1 mL MeOH containing 10% phosphoric acid → vortexed 5 min → incubated (3 h at 37 °C) with vortexing every 1 h → centrifuged (1,000 g, 5 min) and filtered | HPLC–UV | Sim et al. (2020) | |
| Rutin | 1 g sample + 95% EtOH (2 h) → filtered and stored (−20 °C) | HPLC–PDA | Witkowicz et al. (2020) | |
| Gallic acid, caffeic acid, ferulic acid, protocatechuic acid, p-coumaric acid, catechin, OHD, luteolin, apigenin, quercetin, isoquercetin, ellagic acid, velutin orientin, isoorientin, vitexin, isovitexin and rutin | 50 mg sample + acetone:water (4:1 v/v) (24 h shaking) → filtered and centrifuged (4,000 g, 10 min) → filtrate evaporation → dissolved with absolute MeOH | HPLC–DAD | Almuhayawi et al. (2021) | |
| Epicatechin, luteolin, orientin, vitexin, apigenin, naringenin, kaempferol, iso-rhamnetin, quercetin, 4-HBA, caffeic acid, sinapic acid, syringic acid, p-coumaric acid, ferulic acid and chlorogenic acid | Sample + MeOH, water, and formic acid (5 × extraction) → extracts were acidified (pH 2) with 6 M HCl → extraction with DEE → residues were hydrolyzed with 4 M NaOH and 6 M HCl → extraction with DEE → DEE extracts were pooled, evaporated, and diluted in 80% MeOH | HPLC–MS/MS | Dębski et al. (2021) | |
| Rutin and quercetin |
1) Free phenolics (ethanol extract): 1 g sample + 10 mL 80% EtOH (20 min) → centrifuged (6,500 g, 10 min) → re-extraction of residue (2 × with same procedure) → 3 supernatants were pooled and evaporated → diluted (10 mL) with MeOH and stored 2) Bound phenolics (hydrolysis): solid residue (after 3 × EtOH extraction) + 20 mL 2 M NaOH (24 h shaking) → acidified (pH 2) with 6 M HCl → centrifuged → supernatant was extracted with DEE/EtOAc (1:1) → evaporated, diluted (10 mL) with MeOH and stored |
HPLC–UV | Hung et al. (2021) | |
| Orientin, isoorientin, vitexin, isovitexin, Q3R and rutin | Sample + 90% MeOH (30 min UAE) → centrifuged (2,232 g, 10 min) and filtered → re-extraction of residue (1 × with same procedure) → filtered supernatant was pooled → filtrate/supernatant was evaporated |
● Column containing sorbent (100 g Diaion HP-20 resin) ● Extract was loaded to column ● 1st elution (1 L water); 2nd elution (1 L absolute MeOH) → evaporation ● Evaporated extract was freeze-dried and stored (−50 °C) |
HPLC–PDA HPLC–MS |
Jang et al. (2021) |
| Vitexin and isovitexin | 0.25 g sample + 3 mL 70% MeOH (10 min UAE) → centrifuged (1,800 g, 15 min) → supernatant was stored (−18 °C) | HPLC–DAD | Kalinová et al. (2021) | |
| Orientin, isoorientin, vitexin, rutin, catechin, epicatechin, hyperin and p-coumaric acid |
1) Free phenolics (methanol extract): 0.5 g sample + 3 mL 70% MeOH (40 min shaking at 200 rpm in the dark) → centrifuged (8,709 g, 8 min, 10 °C) → re-extraction of residue (2 × with same procedure) → 3 supernatants were pooled → diluted (10 mL) with 70% MeOH, filtered, stored (2 °C) 2) Bound phenolics (hydrolysis): solid residue (after 3 × MeOH extraction) + 20 mL 2 M NaOH (4 h shaking at 200 rpm in the dark) → acidified (pH 3.2–3.4) with 3.5 mL formic acid centrifuged (8,709 g, 8 min, 10 °C) → filtered and stored (2 °C) |
● Sorbent (100 mg Strata-X RP cartridges) ● 1st conditioning (3 mL absolute MeOH); 2nd conditioning (3 mL water) ● 30 mL diluted methanol extract (1:9 in water v/v) or 3 mL hydrolyzed extract was loaded → washed with 4 mL water → dried with vacuum pump → elution (2 mL 70% MeOH) ● Eluted extract was filtered and stored (−80 °C) |
HPLC–MS | Živković et al. (2021) |
aQ-Gal-Rha quercetin-3-O-galactorhamnoside, Cy-Gal cyanidin-3-O-galactoside, Cy-Glu cyanidin-3-O-glucoside, Cy-Rut cyanidin-3-O-rutinoside, Cy-Gal-Rha cyanidin-3-O-galactorhamnoside, Q-Glu quercetin-3-O-glucoside, Cy-Glu-Rha cyanidin-3-O-glucorhamnoside, Q3R quercetin 3-O-robinobioside, K3R kaempferol-3-O-rutinoside, DHBA 3,4-dihydroybenzoic acid, THBA 2,3,4-trihydroxybenzoic acid, p-HBA p-hydroxybenzoic, THCA trans-3-hydroxycinnamic acid, 4-HBA 4-hydroxybenzoic acid, OHD ortho-hydroxydaidzein
bThe extractions were performed under lab/room temperature unless otherwise mentioned. EtOH ethanol, MeOH methanol, TFA trifluoroacetic acid, UAE ultrasound-assisted extraction, EtOAc ethyl acetate, n-BuOH n-butanol, HAE homogenizer-assisted extraction, DEE diethyl ether, DES deep eutectic solvent, CCTG a DES composed of choline chloride and triethylene glycol, MSPD matrix solid-phase dispersion extraction
cThe more detailed information is available in Table 3