Roles of Drying, Size Reduction, and Blanching in Sustainable Extraction of Phenolics from Olive Leaves
Abstract
:1. Introduction
2. Typical Preprocessing Means Applicable to Olive Leave Extraction
2.1. Drying
2.2. Size Reduction
2.3. Blanching
3. Future Perspectives
4. Conclusions
Funding
Conflicts of Interest
References
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Main Processing Factors for Phenolic Extraction | Drying & Size Reduction Prior to Extraction | Key Finding(s) | Reference |
---|---|---|---|
Leaves (pre-blanched) assessed as follows: - Optimization via a single-stage extraction (particle size was among the key independent variables) - Further optimized via multistage extraction system (compared to conventional method 40 °C, 48 h) | Drying: oven-dried with an air tray oven (60 °C, 4 h). Size reduction: dry ground and sieved through 0.05, 0.1, 0.2, 0.315, and 1.0 mm. | - Single-stage extraction: Optimized conditions include 0.315 mm particle size, 70% ethanolic extraction, solid-liquid ratio of 1:7 - Multi-step extraction: Optimization with three stages (30 min, 85 °C) improved TPC (166.6 mg/g); Oleuropein (103.1 mg/g); luteolin-7-O-glucoside (33.7 mg/g); verbascoside (16.0 mg/g); apigenin-7-O-glucoside (13.8 mg/g). - Multistage extraction enabled a 10-fold higher antioxidant activity compared to conventional extraction. | [37] |
Steam blanching and hot water blanching (blanching time and particle size of fresh leaves accounted for the key parameters through optimization of blanching) | - For blanching optimization: particle size of fresh leaves ranged: above 20 mm, 20–11 mm, and 3–1 mm. - For extraction: leaves (optimally blanched), air dried (60 °C for 4 h), and ground to 1 mm. | Optimized steam blanching (10 min, 20–11 mm particle size) improved oleuropein extraction (8.28 g/kg leaves d.w.), and antioxidant effects (4 to 13-fold increase, compared to those obtained from non-blanched ones). | [38] |
Extraction solvents (methanol, ethanol, water, and acetone) | Drying: dried at room temperature in the dark. Size reduction: dry ground to pass through a 20-mesh screen. | - Leaves extracted with 80% methanol exhibited higher TPC (392 mg GAE/g extract); total flavonoids (71 mg rutin equivalent/g); total tannins (18 mg GAE/g). - Leaves extracted with ethanol (80%) exhibited DPPH antiradical activity (IC50 = 1082.35 µg/mL). Total antioxidant activity (via linoleic acid system) was 76.36% with 2400 µg/mL extract. | [39] |
Combining supercritical fluid extraction (with CO2) and pressurized liquid extraction (PLE) | Drying: dried in the shade (ventilated). Size reduction: dry ground to 3 mm particle size. | Oleuropein reached 10.44%, 9.5%, and 9.9%, with DPPH scavenging effects of 127.3, 145.3, and 138.6 µg/mL in defatted residues, using water (150 °C), ethanol (60%, 50 °C), and water (50 °C), respectively. | [40] |
Freezing (conventional and liquid nitrogen) and drying (hot air drying and freeze drying) techniques | Drying: hot air-dried (70 °C for 50 min, 120 °C for 12 min) and freeze-dried. Size reduction: dry ground to 0.05 mm particle size. | Using hot air drying (120 °C): - Increased phenolics particularly oleuropein (108.6 mg/g d.w.). - Antioxidant capacity via ferric reducing antioxidant power (FRAP) reached 109 mg Trolox equivalents (TE)/g d.w. | [16] |
Optimization of MAE compared to conventional and UAE | Drying: dried at ventilated room temperature. Size reduction: dry ground to pass through a 60-mesh. | Competitive effectiveness of MAE (5 min, 50% ethanol) in increasing TPC (76.6 mg GAE/g), and flavonoids (5.8 mg quercetin equivalent/g extract). | [41] |
Hybrid extraction protocol (conventional ethanol extraction subsequent with supercritical fluid antisolvent extraction) | Olive leaves with 8% moisture content ground at room temperature to 1 mm particle size. | Concentrated yield of oleuropein powder reached up to 36% (35 °C, 150 bar). | [42] |
Optimization of aqueous extraction using water | Drying: dried at 120 °C for 90 min. Size reduction: dry ground to 0.1 mm. | Maximum TPC (32.4 mg GAE/g) yielded through extraction at 90 °C for 70 min, solid/solvent ratio of 1:60 g/mL Antioxidant capacity, using DPPH and FRAP, reached 85.26 and 91.03 mg TE/g, respectively. | [43] |
Optimization of UAE | Drying: air-dried at 40 °C Size reduction: dry ground to a 0.5 mm | Increased yield of oleuropein (10.65%) using 50% acetone, 60 °C, 10 min. | [44] |
Extraction methods (solvent extraction, UAE, and reduced pressure extraction) | Drying: dried at ambient temperature (no exposure to solar radiation). Size reduction: ground with a high-speed crusher to pass through a 40–60 mesh. | Increased oleuropein via combined UAE and reduced pressure extraction (92.3% extraction efficiency in a single run). | [45] |
Olive leaves (dried and fresh) from different cultivars | Drying: freeze-dried Size reduction: ground to 0.1 mm | - TPC ranged 7.72–24.65 and 2.09–8.44 mg GAE/g in dried and fresh leaves, respectively. - Effective in inhibiting proliferation of human carcinoma cell line (e.g., freeze dried leaves ranged from 0.07 to 2.40 µg phenolic constituents/well). | [26] |
- Extraction methods (MAE, Soxhlet) - Extraction solvents | Drying: open air-dried in the dark. Size reduction: ground and sieved (<2 mm) | Higher TPC (76.1 mg GAE/g), and antioxidant activity (78.0 mg TE/g) in Soxhlet extracted leaves (50% ethanol). Oleuropein was the key component. MAE was comparably effective. | [46] |
Extraction methods (MAE, UAE, maceration) | Drying: oven-dried (24 h, 40 °C). Size reduction: ground to pass through a 60-mesh. | MAE extracts (86 °C, 3 min) exhibited higher TPC (104.22 mg GAE/g), with 90.03% antioxidant activity. | [47] |
- Preprocessing leaves: drying, non-drying (fresh leaves) - Solvent variations | Drying: freeze-dried (−50 °C, 36 h, 0.08 mbar); hot air oven dried (120 °C, 8 min). Moisture content < 1%. Grinding: milled using a blender | - Hot air-dried leaves extracted by 30% ethanol exhibited highest TPC (151 mg/g d.w.), with DPPH-scavenging activity of 922 µmol TE/g. - The use of water (100%) comparably effects on increased TPC (144 mg/g) of hot air-dried leaves. | [48] |
- Successive extraction techniques - Samples: Olive mill leaves and collected leaves from olive trees | Drying: air-dried Size reduction: ground to 1 mm particle size | - TPC in extracts from olive mill leaves: 4476–6167 mg GAE/100 g. - Extracts from Olive tree leaves (UAE prior to alkaline extraction) contained TPC around 13,108 mg GAE/100 g; oleuropein (12,694 mg/100 g); luteolin 7-O-glucoside 903 mg/100 g; with antioxidant efficiency of 59,651 µmol TE/100 g - Highest concentration of oleuropein in olive mill leaves was 1790 mg/100 g extract. | [49] |
Optimization of UAE extraction | Dried leaves were ground to 0.9−2.0 mm prior to extraction | - Extraction with 43.61% ethanol, 34.18 °C, 59 min exhibited increased TPC (43.825 mg GAE/g dried leaves). - Total flavonoids (31.992 mg catechin equivalents/g dried leaves) through 70% ethanol, 34.44 °C, 60 min. - DPPH inhibiting capacity ranged 89.3%–90.5% | [50] |
- Extraction solvents (ethanol, methanol, acetone, and water) -Extraction methods (MAE and maceration) | Drying: dried in the shade Size reduction: ground to pass through a 60-mesh size screen | TPC using ethanol (50%) represented 88.298 and 69.027 mg GAE/g extract d.w. via MAE and maceration, respectively. | [51] |
Pressurized liquid extraction using water and ethanol | Drying: dried at ambient condition (not exposed to solar radiation) for about 50 days (depending on relative humidity). Size reduction: cryogenically ground using liquid nitrogen. | - TPC yielded 58.7 and 45.8 mg GAE/g, using water (200 °C) and ethanol (150 °C), respectively. - Through water extraction, hydroxytyrosol was the principal phenolic component (up to 8.542 mg/g extract). Through ethanol extraction, oleuropein was the principal component (up to 6.156 mg/g extract). - Extraction with water (200 °C), and ethanol (150 °C) showed effective DPPH scavenging activities (EC50 = 18.6 and 27.4 µg/mL, respectively). | [52] |
Solvent extraction (80% methanol) | Dried/micronized olive leaves (commercial powders) | - Extraction enabled TPC up to 131.7 mg GAE/g leaves d.w.), total flavonoids with 19.4 mg quercetin equivalents/g, and oleuropein 25.5 mg/g d.w. - Antioxidant effects: 281.8 mg TE/g, and EC50 13.8 µg/mL using FRAP and DPPH, respectively. | [53] |
Effect of drying on supercritical extracts | Drying: conveyer belt dryer (air temperatures range: 50, 60 and 70 °C; residence time: 180, 120 and 60 min). Size reduction: ground with a knife mill for 5 min, and sieved (274 µm particle mean diameter). | Drying at 60 °C for 120 min presented higher TPC (36.1 mg GAE/g d.w.) in supercritical extracts, with 73% DPPH inhibiting activity, EC50 = 1.1 µg/mL | [54] |
- Microencapsulation of olive leaves - Frying methods: starch gluten fried dough added with microencapsulated leaves | Drying: pre-blanched leaves dried in force air oven (at 45 °C for 18 h). Grinding device: windmilled. | - Olive leave extract: TPC was 25.7 mg GAE/mL extract; oleuropein was 28.4 mg/mL extract: EC50 = 0.15 mg GAE/mL extract (DPPH) and 109 µmol TE/mL extract (FRAP). - Highest TPC in atmospheric fried dough containing microencapsulated leaves. | [55] |
Olive leaf extract (80% ethanol) and fractions | Drying: dried at 40 ± 5 °C for 6 h Size reduction: ground to pass through a 20–30 mesh | - Ethanolic extract (80%) contained TPC (148 mg/g); total flavonoids (58 mg naringin equivalents/g); oleuropein (the main phenol, 102.11 mg/100 g). Rutin, vanillin, and caffeic acid (minor phenols) represented 1.38, 0.66, and 0.31 mg/100 g, respectively. - Among the fractions: butanol fraction showed greatest antioxidant activity with highest TPC (175 mg/g), and flavonoids (75 mg/g). | [56] |
Optimization via UAE extraction | Drying: air-dried at 25 °C for 7 days. Size reduction: coarsely ground using mortar and pestle. | Compared to maceration, oleuropein increased (30%) with UAE (70% ethanol, 25 °C, 2 h, solid: solvent ratio of 1:5). | [57] |
Extraction kinetics and temperature with UAE and conventional | Dried in a tunnel microwave dryer (70 °C, 1200 W, 10 min) and ground prior to extraction. | - Oleuropein, TPC, and antioxidant capacity increased with the rise of temperature (through both UAE and conventional). - Oleuropein ranged from 6.48 to 6.65 g/100 g d.w.) through UAE that enabled 88% oleuropein extraction in the 1st min. - Using UAE at low temperature (10 °C) competitively exhibited higher oleuropein (5.71 g/100 g d.w.) in 10 min, compared to the conventional (5.15 g/100 g d.w.). | [58] |
Drying of aqueous extracts (freeze-drying and spray-drying) | Leaves (after being washed) kept in the shade (48 h), and ground (80-mesh screen). | - Freeze-dried extracts: TPC (446.63 mg GAE/g d.w.), total flavonoids (298.16 mg quercetin/g), tannins (117.32 mg GAE/g), with 96.57% antioxidant activity. - Spray-dried extracts: TPC (442.84 mg GAE/g d.w.), flavonoids (396.4 mg quercetin/g), tannins (128.71 mg GAE/g), with 96.05% antioxidant activity. | [25] |
Optimization of extraction conditions including drying methods and solvent types/ratio | Drying methods: shade-drying; microwave (2450 MHZ, 80 sec); and vacuum (– 0.5 bar, 55 °C, 24 h). Size reduced by grinding. | - Microwave drying of fresh leaves provided the highest TPC (6.45 g GAE/100 g dried leaves). - Favorable extraction conditions (40% ethanol 60 °C, 120 min) enabled high antioxidant activity (IC50 = 18.92 µg/mL), with a TPC around 6.63 g/100 g. | [59] |
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Safarzadeh Markhali, F. Roles of Drying, Size Reduction, and Blanching in Sustainable Extraction of Phenolics from Olive Leaves. Processes 2021, 9, 1662. https://doi.org/10.3390/pr9091662
Safarzadeh Markhali F. Roles of Drying, Size Reduction, and Blanching in Sustainable Extraction of Phenolics from Olive Leaves. Processes. 2021; 9(9):1662. https://doi.org/10.3390/pr9091662
Chicago/Turabian StyleSafarzadeh Markhali, Fereshteh. 2021. "Roles of Drying, Size Reduction, and Blanching in Sustainable Extraction of Phenolics from Olive Leaves" Processes 9, no. 9: 1662. https://doi.org/10.3390/pr9091662