Ultrasonically assisted Extraction of Coffee0 pages

Using Ultrasonics in Coffee Processing: The Extraction of Caffeine and other
Active Compounds
Kathrin Hielscher, Hielscher Ultrasonics GmbH, kathrin@hielscher.com

Coffee – made from roasted coffee beans - is a very popular drink that is worldwide
consumed. Besides to its vitalizing impact if consumed as a stimulant drink, the compounds
of coffee are of interest for the food, pharmaceutical (e.g. in pain relievers) and cosmetic
industry as used as valuable additives in various products. This applies especially for the
caffeine (1,3,7-trimethylxanthine) and the antioxidants, which are known for their positive
effects on the human health. Coffee contains, amongst others, phenolic diterpenes such as
cafestol and kahweol, and ascorbic acids, which are known for their antioxidative activity.
Epidemiological studies suggest that coffee’s ingredients may have a preventive effect on
several chronic diseases, including type 2 diabetes mellitus, Alzheimer’s disease, Parkinson’s
disease, and liver diseases such as cirrhosis and hepatocellular carcinoma.
Ultrasonics is a well known and proven tool for many different applications in various
industries. A very successful application is the ultrasonic extraction. Thereby, the ultrasonic
cavitation effects on the cell material causing cell disruption and the release of the
intracellular matter.
Ultrasound
To ensure a more easy understanding of the ultrasound assisted extraction procedure, the
effect of ultrasound in liquids must be explained.
Ultrasound - introduced in liquids - causes locally very extreme effects. When sonicating
liquids at high intensities, the sound waves that propagate into the liquid media result in
alternating high-pressure (compression) and low-pressure (rarefaction) cycles, with rates
depending on the frequency. During the low-pressure cycle, high-intensity ultrasonic waves
create small vacuum bubbles or voids in the liquid. When the bubbles attain a volume at
which they can no longer absorb energy, they collapse violently during a high-pressure cycle.
This phenomenon is termed cavitation. During the implosion very high temperatures
(approx. 5,000K) and pressures (approx. 2,000atm) are reached locally. The implosion of the
cavitation bubble also results in liquid jets of up to 280m/s velocity. [Suslick 1998] By these
extreme forces sonolysis occurs, cell walls are disrupted, and intracellular material is
extracted.
The ultrasonically assisted extraction is an inexpensive, simple and efficient alternative
compared to conventional extraction techniques. The main advantages of ultrasound in
solid–liquid extraction include the increase of extraction yield and faster kinetics. Ultrasonic
extraction is a frequently used technique for the extraction of plant materials using liquid
solvents and is proven for a fast and more complete extraction process in comparison with
traditional methods because the surface area between the solid and liquid phase is
significantly larger due to the cell disruption and particle dispersion.
By the use of sonication also the operating temperature can be reduced, allowing the
extraction of temperature-sensitive components. Compared with other novel extraction