Table 2.

Summary of the application of DES in extraction of proteins.

DES	Sample Extract	Operating Conditions	Findings	Reference
Protein (solid–liquid extraction)
Choline chloride-butanediol	Oat proteins	Extraction temperature: 80 °C Time: 90 min	-A total of 55.72% protein content was recovered. -The oat proteins extracted by DES have high protein content, solubility, foaming capacity, and stability.	[90]
Choline chloride-glycerol	Soy proteins	Extraction temperature: 60 °C Liquid/solid ratio: 10.3 Stirring speed: 873 rpm Time: 3.9 h Water content: <15 wt %	-Higher protein yield (0.3462 g) was obtained as compared to the conventional alkali solution acid precipitation method (0.3192 g). -The soy protein extracted by DES showed better heat resistance and stronger hydrophobicity than commercial soy proteins.	[91]
Choline chloride-levulinic acid	Bamboo shoot	Extraction temperature: 80 °C Liquid/solid ratio: 30 mg/mL Water content: 40% v/v Time: 50 min	39.16 mg/g protein extraction yield was obtained, significantly higher as compared to conventional extraction method using sodium hydroxide (23.88 mg).	[92]
Carboxylate salt-urea	Proteins from brewer spent grains	Extraction temperature: 80 °C Time: 4 h Water content: 10 wt %	79% extraction yield (w/w) with >50% protein content was obtained.	[93]
Betaine-propylene glycol (B: PG)	Proteins from sardine processing residues	Extraction temperature: 80 °C Molar ratio of B:PG: 1:3 Solid/liquid ratio: 1:80 g/g Time: 18 h	-162.2 mg/g protein yield was obtained. -The extracts increased the antioxidant and antimicrobial activity by 3-fold and more than 250-fold, respectively, when compared with water.	[94]
Choline chloride-acetic acid (CHCL: AA)	Proteins from pomegranate peels	Molar ratio of CHCL:AA: 1:2 Water content (molar ratio): 15 Amplitude: 60% Time: 15 min	-19.2 mg/g of protein was obtained. -The hydrolyse obtained from proteins extracted by DES presented high antihypertensive capacity.	[95]
Choline chloride-polyethylene glycol (PEG)	Pumpkin seed protein	Extraction temperature: 43 °C Liquid/solid ratio: 28 g/mL Microwave power: 140 W DES concentration: 28% w/w	The extraction yield was 93.95% (w/w) (extraction was assisted by microwave irradiation) and the precipitation rate of pumpkin seed protein was 97.97, with a precipitation time of only 4 min by using isoelectric point-ethanol-PEG 200 DES ternary coprecipitation method.	[96]
Protein (liquid–liquid extraction)
Choline chloride-glycerol	Bovine serum albumin (BSA)	Amount of DES: 1.3 g Concentration of salt solution: 0.9 g/mL Temperature: 30 °C	-98.16% of BSA was extracted into the DES-rich phase of ATPS. -32.96% of back-extraction efficiency was achieved.	[88]
Choline chloride-urea, tetramethylammonium chloride-urea, tetrapropylammonium bromide-urea, choline chloride-methylurea	Bovine serum albumin (BSA)	Amount of DES: 1.4 g Concentration of salt solution: 0.6 g/mL Temperature: 40 °C	The extraction efficiency was in the range of 99.94–100.05%.	[97]
Tetrabutylammonium bromide-glycolic acid	Lysozyme from chicken egg white	Amount of DES: <1.0 g Amount of salt: <0.25 g Temperature: 35 °C	->98% of lysozyme was extracted into the DES-rich phase. -91.73% of initial activity of lysozyme was retained after extraction.	[98]
Tetrabutylammonium chloride-polypropylene glycol 400/L-proline-xylitol [TBAC][PPG400]/[Pro][Xyl]	Chymotrypsin	Amount of [TBAC][PPG400]: 1.0 g Amount of [Pro][Xyl]: 1.6 g Amount of protein: 8 mg Temperature: 35 °C	97.30% of extraction efficiency was achieved.	[99]
Betaine-urea	Bovine serum albumin (BSA)	Amount of DES: 1.4 g Concentration of salt solution: 0.75 g/mL Amount of protein: 15 mg Temperature: 30 $°\mathrm{C}$	-98.29% extraction efficiency was achieved. -Back-extraction efficiency was 32.66%.	[100]