ULTRASOUND IN FOOD TECHNOLOGY

Nowadays, power ultrasound is considered to be an emerging and promising technology for industrial food processing. Probably the first question that might be asked about applications of ultrasound in food technology is why use ultrasound. For the answer to this we need only think of two properties of sound to appreciate the possibilities. The first is the use of sound as a diagnostic tool e.g. in non-destructive evaluation and the second is the use of sound as a source of energy e.g. in sonochemistry. These applications involve different frequency ranges of ultrasound and the uses of both ranges in the food industry are an active subject for research and development.

Until recently the majority of applications of ultrasound in food technology involved non-invasive analysis with particular reference to quality assessment. Such applications use techniques that are similar to those developed in diagnostic medicine, or non-destructive testing, using high frequency (>1 MHz) low power (<1 W/cm2) ultrasound. Examples of the use of such technologies are to be found in the location of foreign bodies in food the analysis of droplet size in emulsions of edible fats and oils and the determination of the extent of crystallization in dispersed emulsion droplets.

In recent years food technologists have discovered that it is possible to employ a more powerful form of ultrasound (>5 W/cm2) at a lower frequency (generally around 40 kHz). This is usually referred to as power ultrasound and its history can be traced back to 1927 when a paper was published entitled  “The chemical effects of high frequency sound waves: a preliminary survey” which described the development of power ultrasound for use in a range of processing including emulsification and surface cleaning (Richards and Loomis, 1927). By the 1960’s the uses of power ultrasound in the processing industries were well accepted and this interest has continued to develop (Abramov 1998, Mason 2000, Mason and Lorimer 2002}. In this chapter we will concentrate on possible applications of power ultrasound in the food industry, an indication of the breadth of which is shown in the Table below

Mechanical Effects	Chemical and Biochemical Effects
crystallisation of fats, sugars etcdegassingdestruction of foamsextraction of flavourings filtration and drying freezing mixing and homogenisation precipitation of airborne powders tenderisation of meat	bactericidal actioneffluent treatmentmodification of growth of living cellsalteration of enzyme activity sterilisation of equipment

 The potential use of this novel technology to produce permanent changes in food materials in liquid systems is through the generation of intense cavitation. This can lead to the inactivation of microorganisms and enzymes for food preservation or decontamination by ultrasonic irradiation demonstrates the benefits of ultrasound (alone or combined with heat and high-pressure techniques) as a food preservation tool. In addition there are an increasing number of industrial processes that employ power ultrasound as a processing aid including the mixing materials; foam formation or destruction; agglomeration and precipitation of airborne powders; the improvement in efficiency of filtration, drying and extraction techniques in solid materials and the enhanced extraction of valuable compounds from vegetables and food products. 

 References:

1.  The use of ultrasound in food technology, T.J.Mason, L.Paniwnyk and J.P.Lorimer, Ultrasonics Sonochemistry, 3, pp253-260 (1996).

2. Ultrasound as a Preservation Technology, T.J.Mason, L.Paniwnyk; F.Chemat, Chapter 16 of Food Preservation Techniques, eds P.Zeuthen and  L.Bّgh-Sّrensen, pp 303-337, Woodhead Publishers (2003).

3.  Potential for the use of ultrasound in the extraction of antioxidants from Rosmarinus officinalis for the food and pharmaceutical industry, S.Albu, E.Joyce, L.Paniwnyk, J.P.Lorimer and T.J.Mason,. Ultrasonics Sonochemistry 11, pp 261-265  (2004).

4.  Applications of Ultrasound, T.J.Mason, Enrique Riera, Antonio Vercet and Pascual Lopez-Buesa, Chapter 13 of Emerging Technologies for Food Processing, ed Da-Wen Sun, pp 323-352, Elsevier (2005).