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Application of ultrasound

Ultrasound in food processing

The preface to this book explains why ultrasound processing is becoming more important in the food industry. It can be used at higher powers to create changes in structure, temperature increases, homogenisation and food preservation, while at lower powers it can be used for process monitoring and food characterisation.

It is a relatively portable and inexpensive technique compared to some competing technologies. The ability of ultrasound to differentiate between small changes in food structure is also an important feature.

The book has three main parts: the first deals with the fundamental properties of ultrasound, while the second and third consider applications at low and high intensities. This is a good, logical structure. There are 45 contributors covering a wide range of topics.

Part 1, Fundamentals of Ultrasound, contains a description of ultrasonic generation, detection and propagation at various intensity levels. This is a good feature of the book, which will help non-specialists to follow some of the technical content in later chapters. It is at a basic level, but more detail of ultrasonic transduction and propagation properties is provided subsequently.

Part 2, Low intensity Ultrasound Applications, represents an in-depth analysis of the ways in which ultrasound can be used to characterise, monitor and control processes in food production. It is split into two main parts: Section 2.1 investigates the ways in which various parameters of the food can be measured and/or used to control food processing, and Section 2.2 contains more detail of how these measurements can be made In terms of equipment and procedures.

A detailed mathematical study of emulsions and their characterisation is provided, which, although necessary to understand the particle size distribution (PSD) within an emulsion, may be beyond some readers. The mainly practical description of measurements in bread dough and cake batter, using contacting ultrasonic devices is valuable.

The flexibility of ultrasound is very well illustrated, showing that various meat products can be measured in terms of fat levels and crystallisation (particularly dry-cured meat products, such as Iberian pork). Other sections consider fat/water content and textural properties, followed by a discussion of much simpler, liquid edible oils, which can be characterised using ultrasound. A detailed mathematical model is proposed for interactions of ultrasound with a complex liquid, together with information on how pressure and temperature variations can affect a measurement.

Section 2.2 contains a very wide-ranging review of air-coupled ultrasonic transducers, which are relevant to many different food-related measurements, where contact with the material is unwanted. Acoustic microscopy is also considered, which allows visualisation of the internal structure of many different food types.

In Part 3, High-Intensity Ultrasound Applications, Section 3.1 considers ultrasonic applications for liquids at high intensities. The use of ultrasound to inhibit microorganisms and enzymes without changing food structure is addressed, concluding that ultrasound is best used in conjunction with heating. In contrast to this, the deliberate use of ultrasound to change a structure by creating an emulsion and the advantages of ultrasonic processing over alternative emulsification techniques are then discussed.

High-intensity ultrasound (HIU) is shown to be useful for creating enhanced osmotic dehydration which, while not able to completely remove moisture from a product, can be used as a pre-treatment before drying by more conventional means.

The use of HIU to extract chemical species from plants as additives to food, herbal extracts etc. is also considered.  Both the mechanisms involved and the role of cavitation in ultrasonically-assisted extraction are described in some detail, as are the challenges of integrating such ultrasonic techniques within the food processing industry.

Section 3.2 considers HIU in applications involving gases and supercritical fluids. The process of manipulating droplets in air via ultrasonic levitation, translation and mixing is discussed first. This is followed by an analysis of how air-coupled transducers can be used in ultrasonically-assisted drying. A final chapter considers microbial and enzyme inactivation within super-critical fluids. These fluids are typically gases at room temperature, but become super-critical at elevated temperatures and pressures, when they exhibit a liquid- like density with gas-like properties, such as diffusivity, making them suitable for enhancing ultrasonic treatments for microbial and enzyme interaction.

Section 3.3 looks at the changes that HIU makes to food structure and constituents. It examines how the structure and function of proteins can be changed within a food material and discusses the effects of HIU on physical properties of carbohydrates, such as depolymerisation and a change in molecular weight. Uses in aiding various biochemical processes, including hydrolysis and fermentation, are also described.

Finally, the use of HIU to change the properties of lipids, including their crystallisation times, resultant microstructure and solid fat content, is addressed along with the extraction and degradation of anthocyanins.

This is an excellent, well-balanced book in many respects, covering a wide range of topics related to ultrasound/ food interactions.

All chapters are very well written, with enough technical content to keep the reader interested. A particular feature is the number of references provided by each author, which make the book an up-to-date precis of current research, with sufficient background and links to other work to underpin each specific area. For anyone wishing to embark on this area of research, this is an invaluable book written by experts in the field and is highly recommended.

ULTRASOUND IN FOOD PROCESSING – RECENT ADVANCES

Editors Mar Villamiel, José V. García-Pérez, Antonia Montilla, Juan A. Cárcel and José Benedito

Publisher Wiley, 2017

Price ebook £135.99

Hardback £150

Reviewer Professor David Hutchins, School of Engineering, University of Warwick, Coventry CV4 7AL, UK

Email D.A.hutchins@warwick.ac.uk

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