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S. M. ALZAMORA¹, S. N. Guerrero¹, and A. López-Malo². (1) Department of Industry, University of Buenos Aires, School of Natural and Exact Sciences, Ciudad Universitaria, Buenos Aires, 1428, Argentina, (2) Food Engineering Department, Universidad de las Américas, Ex Hacienda Santa Catarina Mártir, Cholula, Puebla, 72820, Mexico

A number of nontraditional preservation techniques are being developed to satisfy consumer demands in nutritional and sensory aspects, convenience, absence of synthetic additives, low energy demand, and environmental safety. Among these, ultrasound has not been very much explored, although it is not a new method. It got its start in 1917 and since the 1920s many papers on the killing effect of ultrasonics have appeared. The lethal effect of ultrasound has been attributed to the cavitation phenomenon. When mechanical vibrations of high frequency are intensified by the horn, alternate compressions and rarefactions form millions of microscopic bubbles or cavities containing gas and vapor, which expand during the negative pressure excursion, and implode violently during the positive excursion with the release of large amounts of energy. The implosion (known as cavitation) generates very high temperatures (+/-5,500ºC) and pressures (+/-50 MPa) within the bubbles and the molecules of the vaporized reaction mixture are fractured, forming highly reactive free radicals. This mechanical shock causes microscopic turbulence and/or thinning of the boundary layer at the solid-liquid interface film and/or the formation of microjects of solvent which impact on the solid surface causing pitting and erosion. Ultrasound treatment of foods is unlikely to become a commercial preservation process on its own, but it can be applied in combination with other stress factors or used to complement conventional processes. This presentation focus on the developments related to the ultrasound applied to food preservation. The combined effect of sonication and other treatments (heat, high pressure, heat–high pressure, reduction of pH, addition of preservatives) on the behavior of pathogenic and spoilage microorganisms as well as the role of critical process variables (amplitude and frequency of sonication, sample volume, shape of the vessel) are summarized.