Olive leaf extracts are a potent dietary supplement and therapeutic as it contains strong antioxidants such as the polyphenols oleuropein, hydroxytyrosol and verbascoside. Ultrasonic extraction is highly efficient technique to release and isolate bioactive compounds such as polyphenols, flavones and terpenoids from olive leaves.

Olive Leaf Extract

Olive (Olea europaea) leaves, an agricultural waste or by-product, are a great source os natural antioxidants. Olive leaves contain various polyphenols (also known as biophenols), such as oleuropein and oleacein. Polyphenols occur naturally in plants and contribute to the health benefits of olive leaf extract. Besides polyphenols, the leaves of the olive tree are rich in antioxidants, such as ligstroside isomers, hydroxytyrosol, tyrosol and caffeic acid.
Olive leaf extract is the concentrate of phytochemicals in olive leaves and contains thereby a high amount of powerful antioxidants. Olive leaf extract is traditionally used to boost the immune system. For instance, it is administered to ameliorate symptoms of the common cold, coughs, and sore throats.
Furthermore, research suggest that the polyphenols in olive leaf extract might reduce the risk of cardiovascular diseases, lower cholesterol levels, help with weight loss, exhibit antimicrobial effects, and act as anti-cancer agent.
For this reason, extracts from olive leaves (Olea europaea L. folium) are used as an active ingredient in product formulations of pharmaceuticals and dietary supplements. Furthermore, olive leaf extracts are used in nutritional supplements, therapeutics, cosmetics, as well as food and beverages.
Infused Olive Oil: Olive leaf extract is also used to enrich olive oils such as extra virgin olive oil. Fortified with olive leaf extract, the olive oil has a richer flavour profile and the ORAC value of the olive oil is increased. With olive leaf infused olive oils exhibit improved shelf life and higher heat stability as antioxidants scavenge free radicals and prevent rancidity.

Olive Leaf Compounds

The composition of phenolic compounds in olive leaves includes oleurosides (oleuropein, verbascoside), flavones (luteolin, diosmetin, apigenin-7-glucose, luteolin-7-glucose, diosmetin-7-glucose), flavonols (rutin), flavan-3-ols (catechin) and phenolsic derivatives (tyrosol, hydroxytyrosol, vanillin, vanillic acid, caffeic acid). Oleuropein and hydroxytyrosol are the most important phenolic compounds in olive leaves.

Oleuropein

Oleuropein, a non-toxic olive iridoid (a type of monoterpenoid), is a type of phenolic bitter compound. Whilst present in green olive skin, flesh, seeds, and leaves, oleuropein is the most abundantly found in olive leaves. With a content of 6–14% dry weight it is the most prominent bioactive molecule in olive laves. Depending on olive cultivar, soil and harvest time, the oleuropein content can even rise up to 17–23% dry weight.

Hydroxytyrosol

Hydroxytyrosol is a metabolite of oleuropein. Both molecules are known for their powerful antioxidant activity, which contribute be to some of the antioxidant, anti-inflammatory, and disease-fighting activities of olive oil. Hydroxytyrosol has one of the highest know ORAC (oxygen radical absorbance capacity) values observed in natural antioxidants.

A full-spectrum olive leaf extract contains numerous polyphenols, antioxidants and other phytochemicals, which have synergistic effects. Ultrasonic extraction is a reliable extraction technique, which releases all phytochemicals from the olive leaves and produces thereby a highly potent broadband extract.

What is Ultrasound and Ultrasonic Extraction?

Ultrasound is defined as sound vibrations with more than 20kHz, i.e. more than 20,000 oscillations per second. This is the area that is above the human hearing spectrum. Ultrasound thus covers a very large range of acoustic vibrations, which means that numerous different applications fall into the field of ultrasound. The best-known examples of use include imaging procedures at the doctor’s, parking assistance in cars and the non-destructive testing of materials. For the examples mentioned high-frequency, non-destructive ultrasound is used.
High-power ultrasound is defined as high-intensity, low-frequency sound waves with a frequency of approx. 20-60kHz. These energy-dense sound waves generate alternating high pressure cycles (compression) and low pressure cycles (rarefaction) in liquids. During a low pressure cycle, the high energy ultrasonic waves create small vacuum bubbles or voids in the liquid. When these bubbles reach a volume where they cannot absorb further energy, they burst during a high pressure cycle. This bubble implosion phenomenon is known as cavitation.
Cavitation creates local hot spots in the liquid or slurry, which can reach temperatures of up to 5000K and pressures of up to 2000atm. In addition, the implosion of the cavitation bubbles creates jets of liquid at speeds of up to 280 m/s. These locally occurring extreme conditions cause plant cells to burst, so that bioactive substances that are entrapped in the interior of the plant cell are released. This means, acoustic cavitation disrupts plant cells and leads to higher diffusion of intracellular molecules into the extraction solution (solvent), thereby enhancing mass transfer. Higher mass transfer means higher extraction rate. Therefore, ultrasonic probes are one of the most widely used tools to produce high-quality extracts from botanicals such as herbs, leaves, fruits and other plant materials.
Ultrasonic extraction offers various advantages such as complete extraction / very high yields, reduced extraction time, improved efficiency, compatibility with any solvent, and being a non-thermal extraction method.

The figure shows the ultrahigh-performance liquid chromatography with a diode-array detector (UHPLC-DAD) chromatogram of ultrasonically extracted olive-leaf phenolics. Peaks 1 and 2 were detected at 325nm (red lines), while peak 3 (blue line) was detected at 280nm.
picture and study: Giocometti, J. et al. (2018)

Olive Leaf Extracts Produced by Sonication

The extreme environmental conditions in the “hot spot” zone of the ultrasonic cavitation have various effects on the plant material and its extractability. This includes overcoming the selective permeability of the cell membrane, the increased exchange of substances between the cell interior and the solvent, the mechanical cell disruption and the release of intracellular substances (i.e. phyto-chemicals such as oleuropwin, hydroxytyrosol, gallic acid etc.). These effects result in a high yield of high quality extracts within a very short sonication time. A 400 watt ultrasonic processor such asHielscher’s UP400St can process a 10 litre batch of botanical slurry within 5-8 minutes. The industrial ultrasonicators process the slurry consisting of plant material and solvent in continuous flow. The medium is pumped through an ultrasonic reactor and sonicated there. On an industrial scale, a UIP4000hdT (4kW) can achieve approx. 3L/min.
Due to the high extract yield and process speed, ultrasonic extraction is particularly efficient. Therefore, sonication has been rapidly adapted by multiple extract manufacturers which produce high quality extracts, e.g. CBD, cannabinoids, vanilla, algae, ginger, and numerous other botanical extracts. Ultrasonic cavitation can achieve an extract yield of 95-99% of active compound contained in the botanicals. For instance, research showed a 99,27% extraction efficiency for the release of total phenolics from olive leaves. (Luo, 2011) The ultrasound process can be optimally adapted to the raw material and the desired extract quality by adjusting the process parameters (ultrasonic amplitude, temperature, pressure, viscosity).
Ultrasonic extraction is compatible with almost any kind of solvent. For ultrasonically-assisted olive leaf extraction, 80% aqueous ethanol has been found most efficacious. But the extraction yield for specific phytochemical compounds can be changed by choosing another solvent with different polarity (e.g. methanol).
Interested in increasing your extra virgin olive oil yields during malaxation? Then click here to learn more about ultrasonic malaxation of EVOO!
 

Advantages of Ultrasonic Extraction Systems

The advantages of ultrasonic extraction are the high extraction yield, the free choice of solvent (e.g. water, ethanol, water-ethanol mixture, olive oil, etc.), as well as the simple and safe operation. Due to the intensive mechanical forces of sonication, ecological and mild solvents such as water, ethanol etc. are usually sufficient to achieve an extraordinary extraction rate and yield. As a result, ultrasonic extraction shortens the extraction time and enables a reduced use of solvents or the use of milder, gentler solvents. This means that ultrasonic extraction allows for both, higher extraction rates and healthier extracts (e.g. cold water extracts). Since the process temperature can be precisely controlled during the sonication, thermal decomposition of the extracts due to excessively high temperatures as well as evaporation of the substances are avoided.
Compared to a supercritical CO₂ extractor, the acquisition costs of an ultrasonic extractor are low. The ultrasonic processors can also score points in terms of operating costs, simple, user-friendly operation and occupational safety.

Ultrasonics – for Smaller Quantities up to Industrial Production

A special feature of ultrasonic processing is the linear scalability of the extraction process. Feasibility studies and the production of smaller batches can easily be carried out with a handy ultrasonic device in an open vessel. This makes it easy to test the efficiency and quality of the ultrasonic extraction process. Any results obtained on a small scale can be fully reproduced and up-scaled. The digital control of the ultrasonic extractor and the automatic data logging of the ultrasonic parameters on an internal SD card allow precise monitoring of the process and the reproducibility of constant quality standards. Hielscher Ultrasonics’ product portfolio offers ultrasonic extractors for every scale – from 50 watts handheld devices to 16,000 watts industrial ultrasound for inline production. Thanks to Hielscher Ultrasonics’ decades of experience in ultrasonic extraction and the installation of several hundred ultrasonic extraction systems worldwide, competent and comprehensive advice is guaranteed.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

UIP4000hdT sonicator for inline processing of olive leaves to produce high-quality extracts