Table 1.

The application of non-conventional techniques in the extraction of antioxidants from some foods and medicinal plants.

Source	Compounds Extracted	Extraction Parameters		Extraction Improvement	Reference
		Non-Conventional Method	Conventional Methods
ultrasound-assisted extraction (UAE)
blueberry wine pomace	anthocyanins and phenolics	solvents: 70% ethanol and 0.01% hydrochloric acid; conditions: 400 w, 61.03 °C, 23.67 min	70% ethanol and 0.01% hydrochloric acid; 61 °C, 35 min without ultrasound treatment	increased total anthocyanins from 1.72 to 4.27 mg C3G/g (2.5-fold) and total phenolics from 5.08 to 16.41 mg gallic acid equivalent (GAE)/g (about 3.2-fold)	[42]
papaya	lycopene	solvents: 42.28% ethanol in ethyl acetate conditions: 40 kHz, 800 W, 26.09 min, 50.12 °C	40% ethanol in ethyl acetate (300 mL) 95 °C in a Soxhlet extractor	Recovery of lycopene increased from 68.3 ± 4.1 to 189.8 ± 4.5 μg/g	[43]
carrot	carotenoids	solvents: sunflower oil conditions: 22.5 W/cm2, 40 °C, 20 min	hexane at room temperature for one hour	obtained the β-carotene yield of 334.75 mg/L just in 20 min while the CSE method using hexane as solvent obtained the β-carotene yield of 321.36 mg/L after one-hour extraction	[44]
microwave-assisted extraction (MAE)
Achillea millefolium dust	antioxidants	solvents: 70% ethanol conditions: 170 W, 40 mL/g, 33 s	40% ethanol at room temperature (1:10, v/v) for 48 h	increased total polyphenol content from 135.26 ± 1.72 to 237.74 ± 2.08 mg GAE/g, total flavonoid content from 30.82 ± 2.35 to 42.95 ± 1.32 mg quercetin equivalents (QE)/g, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity from 21.58% ± 0.88% to 71.72% ± 2.12%	[45]
Quercus bark	polyphenols	solvents: ethanol content 33%, methanol content 0.38% conditions: 50 Hz, 45 W, 60 min, pH 10.75, room temperature	the same extraction condition without microwave treatment	increased by 3 times and 2 times respectively for total phenolic content and antioxidant recoveries	[46]
enzyme-assisted extraction (EAE)
wine making by-products	phenolics	solvents: 70% acetone enzyme treatment with 2% viscozyme solution stirred for 12 h at 37 °C or 1 mg/mL pronase solution stirred for 1 h, then extraction with 70% (v/v) acetone in a gyratory water bath shaker at 30 °C for 20 min	the same extraction protocol without enzyme treatment	pronase and viscozyme increased the content of soluble phenolics while reducing the content of insoluble-bound phenolics	[32]
grape skins	flavonoids	solvents: buffer solution containing an appropriate amount of enzyme conditions: 10.52 mg/g Lallzyme EX-V, pH 2.0, extraction at 45 °C for 3 h	70% aqueous ethanol containing 1% formic acid for one day in the dark	improved recovery of anthocyanin contents (from 40,496.19 ± 58.18 to 41,752.95 ± 76.10 mg/kg) and flavan-3-ol contents (from 329.32 ± 2.46 to 345.94 ± 2.88 mg/kg)	[47]
tomato processing waste	lycopene	solvents: hexane/acetone/ethanol (50:25:25 v/v) conditions: 1.5% cellulase/2% pectinase at 4 h of incubation period	without enzyme treatment	increased the yield of lycopene from less than 200 to 847.33 μg/g (cellulase treatment) and to 1262.56 μg/g (pectinase treatment)	[48]
pressurized liquid extraction (PLE)
Aerial parts of Dracoceph-alum kotschyi	phenolics and flavonoids	solvents: methanol conditions: 74 °C, 34 bar pressure, 11.33 min static time, 17.45 min dynamic time, and 0.7 mL/min solvent flow rate	percolated with 1.0 L of methanol at room temperature (25 °C) according to the European Pharmacopeia	improved recovery of total phenolic (from 22.29 ± 0.05 to 30.92 ± 0.03 GAE mg/g), total flavonoids (from 5.042 ± 0.04 to 6.13 ± 0.07 QE mg/g) and luteolin content (from 9550 ± 0.3 to 13,247 ± 0.2 μg/g)	[49]
roots of Scutellaria pinnatifida	phenolics and flavonoids	solvents: methanol conditions: 65.8 °C, 39.2 bar pressure, 12.9 min static time, 18.9 min dynamic time, and 0.76 mL/min solvent flow rate	percolated with 1.0 L of methanol at room temperature	the total phenolic content increased from 196.66 to 396.94 mg/g, and the total flavonoid content increased from 91.3 to 127.78 mg/g	[50]
black bamboo leaves	antioxidants	solvents: 50% ethanol for the total phenolic (TP) and 75% ethanol for total flavonoid (TF) and 25% ethanol for DPPH radical scavenging ability conditions: 1500 psi, 200 °C, 25 min static time	reflux extraction method (~90 °C, 1 L solvent, 60 min)	improved extraction yields from 240 to 500 mg/1 g Dry black bamboo leaves (DL), TP contents from 1510 ± 3.2 to 2682 ± 0.9 mg/100 g, TF contents from 182 ± 2.7 to 657 ± 1.7 mg/100 g	[51]
palm pressed fiber	β-carotene	solvents: n-hexane conditions: 80 °C, 1500 psi, 2 × 10 min static extractions with flush volume 50%	extracted with n-hexane and chloroform in a Soxhlet apparatus for 8 h	obtained total β-carotene and vitamin contents comparable to Soxhlet extraction but with lower total organic solvent and rapid extraction process	[52]
supercritical fluid extraction (SFE)
myrtle leaves and berries	antioxidants	solvents: carbon dioxide conditions: 23 MPa, 45 °C and a CO2 flow of 0.3 kg/h using absolute ethanol as co-solvent with a flow rate of 0.09 kg/h	obtained by hydrodistillation using a Clevenger-type apparatus, for two hours	increased antioxidant capacity (about 20–40 times), polyphenolic contents (about 2 times) and myricetin-3-O-rhamnoside content (about 110–170 times in fruit and about 130–210 times in leaves)	[53]
Prunus persica leaves	phenolic compounds	solvents: carbon dioxide conditions: 60 °C, 150 bar and 6% ethanol co-solvent at a flow rate of 15 g/min and for a duration of 60 min	extracted 3 times with 30 mL of solvent system (acetone:methanol:water:formic acid, 40:40:20:0.1)	the radical scavenging activity value increased from 32.23% to 53.25%	[54]
high hydrostatic pressure extraction (HHPE)
prickly pear beverages prepared with 10% peel and 90% pulp	Phyto-chemical Compounds	400 or 550 MPa, room temperature, 0–16 min	thermally treated at 138 ± 1 °C for 2 s	increased TP content (16%–35%) and antioxidant activity (8%–17%) for Cristal (A) and Rojo San Martin varieties as well as increased the betaxanthin contents (6%–8%) and betacyanin content (4%–7%) for Rojo San Martin variety	[55]
Panax ginseng	phenolic compounds	600 MPa for 1 min at room temperature	conventional steaming	increased the total phenolic contents (from 1.13 to 1.37 mg maltol equivalent/g of red ginseng), especially maltol content (4.38 to 12.61 mg/100 g of red ginseng), also improved the ferrous ion chelating and superoxide dismutase activities	[56]
Pulsed electric field extraction (PEFE)
defatted canola seed cake	polyphenols	10% ethanol 30 V, 30 Hz and 10 s	microwave processing (5 min, liquid/solid ratio of 6.0 and 633.3 W)	less solvent usage, a shorter extraction time	[57]
Borago officinalis L. leaves	polyphenols	acidic water (pH 1.5) 1 to 7 kV/cm, 15–150 μs, 0.04 to 61.1 kJ/kg	the same extraction without PEF treatment	increased the TPC (1.3–6.6 times) and ORAC values (2.0–13.7 times)	[58]
orange peel	polyphenols	distilled water 5 kV/cm, 60 μs, 0.06 to 3.77 kJ/kg, pressurization at 5 bars for 30 min	the same extraction without PEF treatment	increased the naringin content from 1 to 3.1 mg/100 g and hesperidin content from 1.3 to 4.6 mg/100 g	[59]
high voltage electrical discharges extraction (HVEDE)
olive kernel	phenolic compounds	49% ethanol, 66 kJ/kg, pH 2.5	PEF with electric field strength E = 13.3 kV/cm and UAE at 400 W and 24 kHz	more effective polyphenol extraction (255 mg GAE/L for HVEDE versus 140 and 146 mg GAE/L for UAE and PEFE, respectively)	[60]