Table 1.
The main extraction methods of grains’ polyphenols.
| Cereal By-Product |
Extraction Method | Conditions | Polyphenols | References |
|---|---|---|---|---|
| Brewer’s spent grain | Supercritical carbon dioxide (SC-CO2) | - CO2 + Ethanol (0–60%, v/v) - p = 15–35 MPa - t° = 40–60 °C |
Very low quantities of polyphenols | [2,40] |
| Ultrasound Assisted Extraction (UAE) | - Acetone/Water (60/40%, v/v) or NaOH/Water (0.75/99.25%, v/v) - Ultrasound frequency = 20 kHz - t° = 39 → 47 °C |
p-Hydroxybenzoic acid, Ferulic acid, Sinapic acid |
[40,41] | |
| Microwave Assisted Extraction (MAE) | - NaOH (0.75%)/Choline chloride:glycerol - t° = 100 °C |
p-Coumaric acid, Ferulic acid, Syringic acid |
[40,42] | |
| Methanol/Methanol-Water | - VMethanol = 10 mL - t° = 4 °C |
Very low quantities of polyphenols | [40,43] | |
| Water | - VH2O = 50 mL - t° = 25 °C; 80 °C |
4-Hydroxybenzoic acid, p-Coumaric acid, Protocatechuic acid, Vanillin, Catechin, Vanillic acid |
[44] | |
| Ethanol/ Ethanol-Water |
- VEthanol (60–100%, v/v) = 50 mL - t° = 25 °C; 80 °C |
4-Hydroxybenzoic, p-Coumaric acid, Protocatechuic acid, Vanillin, Catechin, Syringic acid |
[44] | |
| Acetone/ Acetone-Water |
- Acetone (60%, v/v) - t° = 60 °C |
p-Hydroxybenzoic acid, Protocatechuic acid, Chlorogenic acid, 8-8′-DiFA, 5-5′-DiFA, 5-5′,8′-O-4′-TriFA, p-Coumaric acid, Ferulic acid, Sinapic acid |
[41] | |
| H2SO4 and NaOH | - H2SO4 + NaOH - t° = 120 °C |
Ferulic acid | [40] | |
| Saponification | - CM = 1–4 M NaOH | Ferulic acid, p-Coumaric |
[45] | |
| Rice bran | Supercritical carbon dioxide (SC-CO2) | - CO2 + Ethanol (0, 5 and 10%) - t° = 40 °C, 60 °C - p = 30, 40 MPa |
(+)-Catechin, Chlorogenic acid, Caffeic acid, p-Coumaric acid, Protocatechuic acid, Cyanidin-3-glucoside |
[2,46] |
| Ultrasound Assisted Extraction (UAE) for black and purple rice bran | - Solvent (20–60%) - t° = 30–60 °C - pH = 2–4 |
[2,46] | ||
| Microwave Assisted Extraction (MAE) | - Methanol (100%) - t° = 185 °C - Microwave power = 1000 W |
[46,47] | ||
| Green method | - Glycerol (10–70%, v/v) - t° = 40–70 °C - Liquid-to-solid ratio = 10–40 mL/g |
[2,46] | ||
| Corn bran | Pressurized alkaline hydrolysis | - CM = 0.5 M NaOH—30% Ethanol - 15% Ammonia/Water - t° = 180 °C |
Ferulic acid, p-Coumaric acid, Vanillin (derived) |
[48] |
| Single alkaline and acid extraction | - VNaOH = 5 mL (2 N NaOH) - VHCl = 5 mL (2 N HCl) |
Vanillic acid, Cis-ferulic acid, p-Coumaric acid, Caffeic acid, Syringic acid, Sinapic acid |
[49] | |
| Single neutral extraction | - VEthanol (50%, v/v) = 10 mL | [49] | ||
| Acetone | - VAcetone (50%, v/v) = 20 mL - t° = 25 °C |
p-Coumaric acid, Syringic acid, Ferulic acid |
[50] | |
| Wheat bran | Supercritical carbon dioxide (SC-CO2) | - CO2 (8 ± 1 kg CO2/h) - t° = 40 ± 2 °C - p = 25.0 ± 1.0 MPa |
p-Hydroxybenzaldehyde, Ferulic acid, Syringic acid, Syringic aldehyde, Vanillic acid, Vanillin |
[51] |
| Ultrasound Assisted Extraction (UAE) | - Methanol/Ethanol/Acetone (70/70/70%, v/v) - Ultrasound frequency = 40 kHz - t° = 50 °C |
[52] | ||
| Steam Explosion | -Ethanol -t° = 224 °C -p = 2.5 MPa |
Ferulic acid predominantly | [53] | |
| Enzymatic Hydrolysis | - Multi-enzyme complex Viscozyme L/Xylanase/Feruloyl esterase | Ferulic acid | [54] |