The disintegration of cell structures (lysis) by means of ultrasound is used for the extraction of intra-cellular compounds or for the microbial inactivation.
In microbiology, ultrasound is primarily associated with cell disruption (lysis) or disintegration (Allinger 1975). 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 The resulting shear forces break the cell envelope mechanically and improve material transfer. Ultrasound can have either destructive or constructive effects to cells depending on the sonication parameters employed.
Under intense sonication enzymes or proteins can be released from cells or subcellular organelles as a result of cell disintegration. In this case, the compound to be dissolved into a solvent is enclosed in an insoluble structure. In order to extract it, the cell membrane must be destructed. Cell disruption is a sensitive process, because the cell wall’s capability to withstand high osmotic pressure inside. Good control of the cell disruption is required, to avoid an unhindered release of all intracellular products including cell debris and nucleic acids, or product denaturation. Ultrasonication serves as a well-controllable means for cell disintegration. For this, the mechanical effects of ultrasound provide faster and more complete penetration of solvent into cellular materials and improve mass transfer. Ultrasound achieves greater penetration of a solvent into a plant tissue and improves the mass transfer. Ultrasonic waves generating cavitation disrupt cell walls and facilitate the release of matrix components.
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