Ultrasound: Advances in Food Processing and Preservation

Daniela Bermudez-Aguirre

• Publisher: Academic Press
• Year: 2017
• Print ISBN:
  9780128045817
• eBook ISBN:
  9780128046142
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Ultrasound is an emerging technology that has been widely explored in foodscience and technology since the late 1990s. The book is divided into three main areas.Chapters 1 to 5 focus on the basic principles of ultrasound and how the technology works on microbial cells, enzymes, and the chemistry behind the process. Chapters 6 to 15 cover the application of ultrasound in specific food products and processes, discussing changes on food quality and presenting some innovations in food ingredients and enhancement of unit operations. Finally, Chapters 16 to 20 present some topics about manufacture of ultrasound equipment and simulation of the process, the use of the technology to treat food industry wastewater, and an industry perspective. The laws and regulations concerning emerging technologies, such as ultrasound, are also discussed, including the new Food Safety Modernization Act. - Provides a clear and comprehensive panorama of ultrasound technology - Contains updated research behind this technology - Brings the current tested product and future uses - Explores potential future use within the food industry

Chapter 1

Engineering Principles of Ultrasound Technology

Sandra E. Kentish University of Melbourne, Parkville, VIC, Australia

Abstract

This chapter describes how ultrasonic waves are formed in ultrasonic baths, with horn transducers, and in other acoustic devices. The range of acoustic frequencies and powers relevant to sonoprocessing is outlined. The concept of acoustic cavitation is explained as the formation of a field of small bubbles within a liquid exposed to ultrasound. It is the repetitive collapse of these bubbles under the influence of the acoustic field that is the dominant cause of most effects used in food processing, as it causes fluid turbulence and microjetting. The extent to which it is effective is a function of the system temperature and pressure, as well as fluid properties such as the surface tension, density, and viscosity. The concept of acoustic nebulization, which is the formation of a fine mist, is also explained.

Keywords

Amplitude; Cavitation; Frequency; Nebulization; Standing wave; Transducer

1.1. Introduction

Sound is simply a variation in pressure, or a vibration, that moves through its environment, be it the atmosphere or a food item. This variation in pressure is usually generated by a mechanical action. For example, if you dropped a book on the floor, the vibration caused by the collision would cause a “bang” sound. Playing the guitar has a similar effect; the vibration of the string causes us to hear music.

In sonoprocessing, these vibrations are used to generate physical and sometimes chemical effects. The approach provides a mechanism to modify food substances in a manner that consumers can appreciate, as it is noninvasive and does not use dangerous radiation. Further, it usually operates at ambient temperature, which means that there can be less damage to native proteins and other bioactives that can be damaged by heat. However, it can be energy intensive and users of the technology must be aware of the potential cost when scaling from a laboratory to a full-scale operation.

1.2. Acoustic Waves

1.2.1. Acoustic Transducers

In ultrasonics, the sound vibration is usually generated by a Langevin piezoelectric transducer. This consists of two ceramic elements that change their size in an accurate and reproducible manner in response to an electric field. Thus if an alternating electric field is applied, the ceramic elements move up and down in a highly reproducible manner (Fig. 1.1). A loudspeaker works in the same way, converting an electric field into audible sound. In an ultrasonic bath, four or six of these transducers are generally placed in a regular pattern underneath the base of the bath.

Figure 1.1 A diagram showing how a Langevin ultrasonic transducer operates when fixed to the underside of an ultrasonic bath.

1.2.2. Frequency and Power

The frequency of the acoustic wave generated (the number of waves per second, f) is determined by the frequency of the electric field applied and this is usually fixed by the instrument provider. Frequencies between 20 and 40 kHz are common for food processing applications such as emulsification and microbial inactivation; these frequencies are just above the frequency of human hearing (20 Hz–20 kHz). This is known as “power ultrasound,” as the sound waves generated are relatively powerful and can generate significant shear fields within the surrounding fluid (Fig. 1.2). Alternatively, higher frequencies (>1 MHz) are used for imaging applications, such as the detection of fat and bone in meat carcasses (Monin, 1998; Kvame and Vangen, 2007; Hopkins et al., 2007), and in acoustic velocity measurements for determination of food composition (Ghaedian et al., 1998; Benedito et al., 2001; Ninoles et al., 2010). In this region, any damage to the food substance is avoided. Frequencies in the 300–600 kHz range can have specific applications to sonochemistry, as this is the zone in which free radical production is maximized.

Figure 1.2 The frequency range of application of ultrasound technology and acoustic phenomena. Adapted from Dalmoro, A., et al., 2012. Intensifying the microencapsulation process: ultrasonic atomization as an innovative approach. European Journal of Pharmaceutics and Biopharmaceutics 80 (3), 471–477.

The acoustic power generated is related to the power supplied by the electrical field, which in turn determines the amplitude of vibration (A). This vibration is generally 25 μm or less (peak to peak) at the transducer surface (Peshkovsky et al., 2013). An ultrasonic bath, or a plate transducer, distributes this vibration over a relatively wide area, so the energy intensity of the acoustic field (I, W/cm²) is low. The intensity falls further as the distance from the transducers increases, due to absorption of the sound waves by the fluid. The extent to which it falls depends upon the density and viscosity of the fluid. This variation in energy intensity throughout the bath or reactor means that care must be taken during experimental work to ensure that samples are always placed at an identical position and that the fluid level is always identically uniform.

The acoustic intensity can be increased by reducing the area over which the vibration occurs. This is achieved by using a horn transducer (Fig. 1.3A), which causes the amplitude to initially decrease to zero (at the nodal point) and then increase in the reverse direction to around 100 μm. More recently, Peshkovsky et al. (2013) have suggested that similar amplitudes can be achieved over broader surface area...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• List of Contributors
• Preface
• Chapter 1. Engineering Principles of Ultrasound Technology
• Chapter 2. Advances in Thermo- and Manothermosonication for Microbial Inactivation
• Chapter 3. Hurdle Technology Using Ultrasound for Food Preservation
• Chapter 4. Advances in Thermosonication for the Inactivation of Endogenous Enzymes in Foods
• Chapter 5. Sonochemistry of Foods
• Chapter 6. Dairy Products Processed With Ultrasound
• Chapter 7. Ultrasound Processing of Fruit and Vegetable Juices
• Chapter 8. Fresh Produce Treated by Power Ultrasound
• Chapter 9. Ultrasound Processing and Food Quality
• Chapter 10. Physical Properties of Sonicated Products: A New Era for Novel Ingredients
• Chapter 11. Removal of Allergens in Some Food Products Using Ultrasound
• Chapter 12. Food Freezing Assisted With Ultrasound
• Chapter 13. Encapsulation of Bioactive Compounds Using Ultrasonic Technology
• Chapter 14. Extraction Processes Assisted by Ultrasound
• Chapter 15. Other Mass Transfer Unit Operations Enhanced by Ultrasound
• Chapter 16. Treatment of Food Industry Wastewater With Ultrasound: A Big Opportunity for the Technology
• Chapter 17. From Research to Production: Overcoming Scale-Up Limitations of Ultrasonic Processing
• Chapter 18. Multiphysics Simulation During Ultrasound Food Processing
• Chapter 19. Opportunities and Challenges of Ultrasound for Food Processing: An Industry Point of View
• Chapter 20. Laws and Regulations for Novel Food Processing Technologies
• Index