Ultrasound
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Contents
General Information
Overview
The development of ultrasound began in the preceding years of the Second World War, for emulsification and surface cleaning technologies. Further applications on animal communication sciences, detection of building flaws, fine chemistry analysis and treatment of disease. In the food sector, there are application to generate emulsions, cell disruption and disperse aggregate materials. Future developments on modification and control of crystallization processes, degassing of liquids, enzymes inactivation, enhanced drying and filtration and the induction of oxidation reactions. Potential aromatic change can be also enabled by the technology.
(Muredzi, 2012)
Advantages
- Rapid, precise and non-destructive analytical tool. Used for texture, viscosity and concentration measurements.
- Automatizing potential.
- Considered clean and green technology and acceptable.
- Foam destruction improving processing speed and potential viscosity management.
- Enhance texture (yogourt, stronger gel structure with greater water holding capacity; changing viscosity, reducing size of particle) and flavors in diary nutrition.
- Extending shelf life of juices, used when bio active and anti oxidant compound retention or enhancement is required
(Paniwnyk, 2014)
- Increase efficiency of mass transfer (Muredzi, 2012)
Disadvantages
- Monitor possible negative effect like oxidation of fats, inactivation of valuable enzymes and denaturation of proteins. Unexpected changes in aroma are also possible.
(Paniwnyk, 2014)
Base
- Ultrasonic technology is based on a form of energy generated by sound waves above 16 KHz. Its propagation in a biological structure induces compression and depression of the medium particles and high amount of energy can be imparted.
- The fundamental effect is to impose acoustic pressure on a continuum fluid. It is a sinusoidal wave dependent on time, frequency and the maximum amplitude wave
- Ultrasound enables the formation of regions of alternating compression and expansion. There is a potential generation of immense pressure, shear and temperature gradient in the medium due to cavitation, this is shockwaves from the collapse of formed bubbles leading to high pressure high temperature regions (5500°C and 50 MPa).Cavitation can result from micro streaming enhancing mass and heat transfer. Cavitation depends on the ultrasound characteristics, product properties and ambient conditions. Ultrasound intensity required to cause cavitation increase markedly above 100 KHz
- Another important phenomenon behind this technology is Ultrasound degassing: process of bubble transport and growth in the nodes and the anti nodes (bubbles smaller than the resonance size). The acoustic pressure at the nodes is zero and in the anti node fluctuate from a maximum to a minimum.
- There is classification of ultrasound according to the frequency: Power Ultrasound (16-100 kHz), high frequency ultrasound (100kHz-1 MHz) and diagnostic ultrasound (1-10 KHz).
- Frequency inversely proportional to bubble size. Low frequency generates large cavitation bubbles resulting in higher temperatures and pressures in the cavitation zones. Cavitation between 16-100 KHz for industrial use.
(Paniwnyk, 2014)
Description of techniques
- The general parameters are three: sound power, sound intensity and sound density characteristics. According to this parameters there is low energy and high energy ultrasound. Low energy (low power and low intensity) is higher than 100 KHz and lower than 1 Wcm-2; not physical nor chemical changes used for food processing monitoring. High energy ultrasound use intensities 10-10000 Wcm-2 and frequencies between 18-100 KHz altering material properties.
- A Liquid medium is essential even if it is only 5% of the overall medium. A source of high energy vibration or transducer which transfer the amplified vibrations to the sonotrode or probe in direct contact with the medium.
- The transducer can be : Piezoelectric (scalability and commercial) or magnetostrictive (generally lower maximum power)
- Process parameters: Energy (input per volume of material) and Intensity (power per surface are of the sonotrode). Pressure (more and more cavitation potential, more rapid but violent collapse of bubbles). Temperature (affecting vapour pressure, surface tension and viscosity; increase the bubble number but dampened collapse) and Viscosity (+-cavitation)
(Paniwnyk, 2014)
Changes in process
Fermentation
The use of the technology enables a reduction in the operation time with higher viable cells count. High potential in the dairy industry.
When microbiological cultures for fermentation are treated by ultrasound, their activity is higher enabling a faster fermentation. In this same way, processing by ultrasound can reduce costs significantly, since fermentation time is shorter.
(Barukčić et al. 2015)
Sterilization
Ultrasound technology, assisting to other processes of sterilization, is effective minimizing the flavor lost, enabling a greater homogeneity and energy savings. The results differ depending on the type of bacteria and very high intensities are need for permanent sterilization ultrasound alone.
Tested life extension of food, enhanced stability. Product quality, texture and flavors can be maintained if process times are kept to a minimum and treatment temperatures are reasonably low.
(Paniwnyk, 2014)
Cases:
Ultrasonic disruption of yeast cells: Underlying mechanism and effects of processing parameters
Innovative Food Science & Emerging Technologies, Volume 28, March 2015, Pages 59-65
Tao Wu, Xiao Yu, Antuo Hu, Li Zhang, Yuan Jin, Muhammad Abid
Influence of high intensity ultrasound on microbial reduction, physico-chemical characteristics and fermentation of sweet whey
Innovative Food Science & Emerging Technologies, Volume 27, February 2015, Pages 94-101
Irena Barukčić, Katarina Lisak Jakopović, Zoran Herceg, Sven Karlović, Rajka Božanić
Pasteurization
The technology can be used as replacement for conventional pasteurization where the precipitation does not occur. Stability increase of food is also possible. There is a reduction in cost compared with conventional methods due to reductions in the operation time. It has a high potential in the dairy industry.
(Barukčić et al. 2015)
Extraction
Ultrasound enables a greater penetration of solvent into cellular materials. Disruption of cellular walls facilitating the release of content. Micro streaming effects for better diffusion. Higher level of dry matter and final content. Improved process for organic compounds within the body of plants and seeds.
Fundamentally implies increasing efficiency of extraction at lower temperature in less time.
(Muredzi, 2012)
- Used in natural compound extraction as natural antioxidants, oils, color, flavors, polyphenols, citrus peel, olive, oil, pam oil, coffee, tea, grape must, carotenoids among others.
- Natural dyes extraction at 80 W, 45° 3h, up to 100% enhanced of the marigold flowers, 25% in pomegranate and 12% in green wattle.
(Paniwnyk, 2014)
Cases:
Applications and opportunities for ultrasound assisted extraction in the food industry
Innovative Food Science & Emerging Technologies, Volume 9, Issue 2, April 2008, Pages 161-169
Kamaljit Vilkhu, Raymond Mawson, Lloyd Simons, Darren Bates
Drying
The technology enables lower process temperature and less processing time. It enables increases from 30% to 60% on heat transfer between a solid surface and a liquid medium. Freezing drying with ultrasound enables the control the size of the crystals.
(Muredzi, 2012)
Cases:
Ultrasonic vacuum drying technique as a novel process for shortening the drying period for beef and chicken meats
Innovative Food Science & Emerging Technologies, Volume 26, December 2014, Pages 182-190
Mehmet Başlar, Mahmut Kılıçlı, Omer Said Toker, Osman Sağdıç, Muhammet Arici
Novel contact ultrasound system for the accelerated freeze-drying of vegetables
Innovative Food Science & Emerging Technologies, Volume 16, October 2012, Pages 113-120
Katharina Schössler, Henry Jäger, Dietrich Knorr
Cooling/freezing
The effect of the ultrasonic technology in the freezing process is related with the pre-existing bubbles in liquids that affect ice nucleation and crystallization. Liquids containing pre-existing bubbles nucleate with a shorter delay. Adding bubbles to liquid samples could be a promising and feasible approach to improve the effectiveness of ultrasound irradiation with great potential for the frozen food industry. (Hu et al, 2013)
Washing products
The ultrasound technology enables an enhancement in microbial count reduction over alone wash. Continuous-flow ultrasonic washing of fresh produce enhance microbial safety. Blockage of ultrasound by produce leaves or other materials should be avoided. Also the variance in the residence-time distribution should be minimized and a near-uniform acoustic field distribution in the washing facility should be assured.
(Zhou & Pearlstein, 2012)
Equipment Cleaning
The technology in situ combined with chemical treatment enables the reduction of chemical use and worker/chemical contact use. Better cleaning speed and cleaning consistency is enabled. Automatic operation and control are possible, additionally to potential on labor, floor space, and energy savings.
(Muredzi, 2012)
High pressure jetting effect potential can happened in solid-liquid systems.
(Paniwnyk, 2014)
Case:
Evaluation of high power ultrasound porous cleaning efficacy in American oak wine barrels using X-ray tomography
Innovative Food Science & Emerging Technologies, Volume 12, Issue 4, October 2011, Pages 509-514
Garth Wayne Porter, Andrew Lewis, Mark Barnes, Ruth Williams
Energy Savings
Potential savings due to the easier mass transfer processes, the energy needed per production unit should be lower as for most unit operation the technology accelerates the process.
Change in Energy Distribution
Use of more electricity increasing the power demand of the site in terms of electricity and potential reduction in terms on thermal energy. Due to the facilitation of the processes, it is also possible to have lower conditions of temperature and energy, broadening the potential sources of energy.
References
- Barukčić, I., Jakopović, K., Herceg, Z.,Karlović, S., Božanić, R. (2015) 'Influence of high intensity ultrasound on microbial reduction, physico-chemical characteristics and fermentation of sweet whey', Innovative Food Science & Emerging Technologies, 27(February), pp. 94-101.
- Hu, F., Sun, D., Gao, W., Zhang, Z., Zeng, X., Han, Z. (2013) 'Effects of pre-existing bubbles on ice nucleation and crystallization during ultrasound-assisted freezing of water and sucrose solution', Innovative Food Science & Emerging Technologies, 20(October), pp. 161-166.
- Muredzi, P. (2012) 'Chapter 5: Ultrasound Processing Technology', in Aleman, M. (ed.) Emerging Non-thermal Food Processing Technologies. USA: CBH books, pp. 167-194.
- Paniwnyk, L. (2014) 'Part III Other not Thermal Technologies: Chapter 15 Application of Ultrasound', in Sun, D. (ed.) Emerging Technologies for Food Processing. UK: Academic Press, pp. 361-377.
- Zhou, B., Feng, H., Pearlstein A. (2012) 'Continuous-flow ultrasonic washing system for fresh produce surface decontamination', Innovative Food Science & Emerging Technologies, 16 (October), pp. 427-435.
