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Ultrason Sonochem. 2014 Jan;21(1):454-60. doi: 10.1016/j.ultsonch.2013.06.007. Epub 2013 Jun 20.

Inactivation of microorganisms by low-frequency high-power ultrasound: 2. A simple model for the inactivation mechanism.

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School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand; School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand; Institute of Food and Agricultural Standardization, China National Institute of Standardization, Beijing 10088, China.


A simple theoretical model based on shear forces generated by the collapse of the ultrasound cavities near the surface of a microorganism is proposed. This model requires two parameters which take into account the number of acoustic cavitation bubbles, and the resistance of the cell wall of the microorganism to the shear forces generated by bubble collapse. To validate the model, high-power low frequency (20 kHz) ultrasound was used to inactivate two microorganisms with very different sizes, viz., a bacterium, Enterobacter aerogenes and a yeast, Aureobasidium pullulans. The inactivation ratio was experimentally measured as a function of sonication time for different ultrasound power and for different initial cell numbers. For both E. aerogenes and A. pullulans the Log of the inactivation ratio decreased linearly with sonication time, and the rate of inactivation increased (D-value decreased) with the increase in sonication power. The rate of inactivation was also found, for both microorganisms, to increase with a decrease in the initial cell number. The fits, obtained using the proposed model, are in very good agreement with the experimental data.


Aureobasidium pullulans; Bacteria inactivation; Enterobacter aerogenes; High-power ultrasound; Theoretical model; Yeast

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