Ultrasounds for vegetable extraction
Plants contain countless phyto-complexes for human and animal use which are of great interest for pharmaceutical, herbalist, cosmetic, health and food industries.
Extraction systems are exhaustive when the right combination of three important elements is carried out: preparation of the vegetable, extraction solvent and extraction method. Some traditional extraction techniques provide for the use of organic solvents, high temperatures and long maceration periods with negative outcomes which one may imagine: damage to health, the environment and deterioration to the active ingredients and vegetable matrices.
The ultrasonic extraction technique breaks the plant cell wall by means of cavitation thus increasing mass conveyance and penetration of the solvent. This enables acceleration of the extraction time achieved only by means of physical action.
Combining ultrasounds with traditional extraction systems enables:
Reduction of operating time;
Reduction of process temperatures;
Control of the use of solvents.
The aim of is to attain certified “organic” products and the advantages are in terms of:
Conservation of the innate properties of the extract.
To sum up, we can utilize the following advantages from ultrasounds:
Use of any kind of liquid solvent, including oil, (depending on the product subjected to treatment, in some cases use of organic solvents is unnecessary);
Low extraction temperatures: prevention of inconveniences caused by high-temperature extraction (deterioration of thermolabile ingredients);
Reduction of extraction times compared to traditional techniques (extraction times with ultrasounds range from 10 minutes to 1 hour);
Total compatibility of the technology with all traditional extraction methods (in any phase);
Control of the process parameters (modulating time, frequency and ultrasonic power).
Some information on industrial vegetable extraction
The main vegetable extraction methods, based on osmosis and diffusion phenomena, used in laboratories and industries, can generally be summarized in:
Extraction with solvents.
The three main alternative industrial extraction technologies, which have high performance ecologically speaking and which respect substances, are:
Supercritical fluids (CO2): suitable for non-polar active ingredients (oils), non-polluting, very expensive;
Dynamic extractors (Naviglio Extractor):a mechanical device with pistons; it induces (during the “release” phase) a negative pressure gradient in the solid matrix, so that extraction is possible at ambient temperature in few cycles, i.e. in short periods of time (1-2 hours);
Ultrasounds: suitable for pre-treatment of vegetable matrices, non-polluting and comparatively low-cost.
Extraction of polyphenols from thyme (thimus vulgaris) with an ultrasonic reactor
An experimental test was conducted to obtain a rapid and complete extraction of polyphenols, optimizing the system in terms of:
- specific ultrasonic power (W / liter)
- amount of vegetable / dilution
- type of solvent: water, water and EtOH cosolvent (ethanol)
- sonication time and mode (continuous / intermittent)
The chemical analyzes are aimed at identifying the yield in total polyphenols, because they are easy to identify, of great interest for pharmaceutical and nutriceutical applications, comparable with many literature data.
There is no mixing for ultrasonic extraction, as a very compact sonication cell (100mL) is used.
The EW20S reactor consists of a main body that ends with a 'barbell horn' type sonotrode and a compact flow cell, with a net volume of about 100mL for the solvent.
As regards the reference test (traditional maceration), the vegetable was immersed in the solvent at about 25 ° C for 24h.
Given the possibility of high specific powers involved, the temperature rise was measured during the tests and the maximum extraction duration was limited in all the tests to not exceed 40 ° C for the vegetable / solvent mixture.
Main parameters for the optimized test:
Vegetal : THYME dry: density 0.21 g / l, 2 / 3mm, herbal tea cut
pre-treatment of veg.: 10 minutes of pre-immersion in water to soak the vegetables
solvent: H2O (60%) / EtOH (40%)
Vegetable / solvent dilution: 1/20
Power: 60 W, pulsed 5s ON / 5s OFF
temperature rise: about 15 ° C
Process type: BATCH, without mixing
reaction cell volume: 100mL
sonication time: 10min.
Results of chemical analyzes
The results of the chemical analyzes on the extracts of the most significant tests follow. The reference test of 24h maceration in is N 1, while the test optimized with ultrasound is N 11.
The analysis was carried out with HPLC at a wavelength of 280 nm (characteristic for this class of compounds). The trend of the graphs (quantity and height of the peaks) highlights the ultrasound efficiency to extract various types of polyphenols in a few minutes (among these, various antioxidants: flavonoids known as proanthocyanidins, leucoanthocyanidins, piconogenols, tannins, etc.).
The analyzes of the samples obtained were carried out by the Institute of Biomolecular Chemistry of the C.N.R. of Padua, in the days immediately following that of the tests.
In summary, the results show an equivalent or greater extraction of polyphenols for the test with ultrasound 11 (duration 10min.), Compared to the extraction by traditional maceration in 24 hours (test 1).
Special Everywave systems for ultrasonic extraction
Everywave has designed and optimized two ultrasound system series:
Thanks to the scalability of ultrasonic processes, research results can be transferred to industrial-scale processes.
Special industrial systems
Everyware has designed special systems with flow cells and a tubular reactor, TRD1L and UDS4L / TBL4L, for applying ultrasounds to vegetable extractions and macerations where high power or continuous-flow operating is required.
These systems can be used in specialized industrial sonochemistry thanks to:
High power which can reach 1000W/l;
Operating in overpressure conditions;
High temperatures up to 150°C.
Standard extraction tanks
For all traditional vegetable extraction applications, Everywave and Unitech have fine-tuned a line of ultrasonic E-tanks® for treating various parts of plants (leaves, flowers, buds, seeds, fruit, roots and bark) both fresh and dried, through both polar and non-polar solvents.
The available models have tanks with the following capacities: 5 litres (for extracting from 2 to 5 litres), 20 litres (for extracting from 5 to 20 litres), 100-250 litres (for extracting from 20 to 250 litres).
These tanks are able to operate at frequencies of 25, 38, 50 kHz and are equipped with:
Slow mixing devices; the mixing power can be directed (upwards or downwards, depending on the extracting solvent used);
Ultrasonic power control and extraction temperature.