Table 2.

Main techniques and extraction systems commonly used for obtaining phenolic compounds from plant materials.

Plant Material	Extraction Technique	Optimised Conditions	Phenolic Compounds	Reference
Rice grains	PLE	Extraction solvent (60% ethyl acetate in methanol), temperature (190 °C), pressure (200 atm) and static time (10 min)	Protocatechuic acid, vanillic acid, vanillin, protocatechuic aldehyde, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, ferulic acid, sinapic acid, guaiacol, p-coumaric acid, caffeic acid, chlorogenic acid, 5-hydroxymethyl-2-furaldehyde, catechin, 5-methylfurfural, ellagic acid and iso-vanillic acid	[23]
Eucalyptus robusta leaf	MAE	Water, power (600 W) for 3 min, and 2% (w/v) solid loading	Phenolic, flavonoid and pro-anthocyanidin compounds	[24]
Picea abies bark	UAE	53% (v/v) Methanol, 63 °C, and 38 mL:1 g (dry) for solid loading	Vanillic acid, syringic acid, p-coumaric acid, ferulic acid, sinapinic acid	[25]
Guaraná (Paullinia cupana) seeds	SFE	40% Ethanol:methanol for 40 min, 40 °C, and 100 bar	caffeine, catechin, and epicatechin	[26]
Fig fruits	LLE	18% Ethanol (w/w), 25% K2HPO4 (w/w), 10–30 °C, and 3% (w/w) for solid loading	More than 75% of phenolic compounds were recovered (gallic acid, chlorogenic acid, syringic acid, (+)-catechin, (−)-epicatechin and rutin)	[27]
White grapes	SPE	C18 cartridges previously conditioned with 30 mL of methanol and 70 mL of aqueous HCl (pH 2). Phenolic fraction eluted with ethanol	Caftaric acid, coutaric acid, fertaric acid, quercetin and kaempferol and their glycosides (3-O-glucoside and 3-O-rutinoside)	[28]

Abbreviations: LLE, liquid–liquid extraction; SPE, solid-phase extraction; UAE, ultrasound-assisted extraction; SFE, supercritical fluid extraction; PLE, pressurised liquid extraction and MAE, microwave-assisted extraction.