Acoustics'08 Paris

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Ultrasound in the Dairy

Dr Shobha Muthukumaran
School of Engineering and Information Technology
Deakin University Pigdons Road
Waurn Ponds, Victoria, 3217 Geelong, Australia

A/Prof Sandra Kentish
Department of Chemical and Biomolecular Engineering
The University of Melbourne Parkville
Victoria, 3010 Melbourne, Australia  

A/Prof Muthupandian Ashokkumar
School of Chemistry The University of Melbourne Parkville
Victoria, 3010 Melbourne, Australia  

Prof Geoff Stevens
Department of Chemical and Biomolecular Engineering
The University of Melbourne Parkville
Victoria, 3010 Melbourne, Australia

Popular version of paper 1pPAd8
"Potential uses of ultrasound in the dairy ultrafiltration processes"
Presented at 6:20 p.m. on June 30, 2008 in Room 352A

All figures referred to in the text are contained in this Power Point and this PDF

One of the major concerns in dairy processing is the handling and processing of whey, a natural by-product produced during cheese making. Whey makes up most of the initial milk volume, contains most of the lactose and about 20% of milk proteins. Until recently, whey was considered a useless waste product and was disposed of indiscriminately in land and surface waters causing considerable environmental impact. Increased environmental regulations, along with the realisation of economic and nutritional value of whey, have gradually led to more beneficial uses. For example, unprocessed whey can be used as feed for animals. However, further uses require processing of the whey to create nutritional value.

Porous membrane filters (Fig. 1) provide an extremely attractive technique for whey processing. They purify and concentrate the whey components, enhancing their utilisation and reducing the pollution problem. Membrane filters can be used to remove lactose and minerals and separate the whey proteins. The resulting whey protein concentrate can be directly added to a number of dairy products such as yoghurt or cottage cheese or it can be sold as an additive for use in a number of food products.

One problem with the membrane filters is that over time the membrane surface becomes blocked and clogged with proteins, making it less effective. This means that frequent cleaning is required (Fig. 2) . This repeated fouling and cleaning cycle of dairy whey filtration significantly affects the efficiency of the process. This project has attempted to use power ultrasound during whey filtration as an alternate and environmentally friendly approach which in turn helps to improve the process economics.

Ultrasonic waves are mechanical vibrations operating at frequencies above the human hearing threshold (in the range of 16 kHz to few megahertz). Power ultrasound (20-100 kHz) is widely used in industry for cleaning and is extremely efficient for this purpose. When ultra high frequency sound waves (ultrasound) are passed through a liquid, they generate a series of chemical and physical interactions in the liquid. Very tiny micro bubbles form, these grow and shrink as each wave of sound passes through them. Eventually these bubbles grow until they collapse. This process is known as acoustic cavitation (Fig. 3). The collapse of these bubbles leads to shock wave formation (Fig. 4), microjet formation (Fig. 5) and a turbulent flow of the liquid surrounding the cavitation bubbles, called acoustic streaming (Fig. 6). The bubble collapse (cavitation) and acoustic streaming can help prevent the membrane filters getting clogged by making the cake layer more porous and by loosening the cake so that it can be removed during wash out.

There are four effects of ultrasound, which can be packaged together to improve the filtration and or cleaning processes:

During the production cycle, the use of ultrasound reduces both pore blockage and the compressibility of the cake layer (Fig. 7). This leads to higher product recovery and the potential for longer production cycles. Our results show that the ultrasound can enhance the productivity by 20 to 70 % by reducing the extent of the clogging and enhancing the mass transfer which results in savings on processing costs. During the cleaning cycle, ultrasound increases cleaning efficiency which has the potential to reduce both total chemical consumption and system downtime. The result suggests that the ultrasonic influence is significant when cleaning is carried out for up to 10 minutes and almost all of the ultrasonic effect occurs in the first 10 minutes of ultrasound. We observe no deterioration in cleaning effectiveness or membrane condition, which implies that sonication has not damaged the membrane itself. Similarly, there was no change in the chemical nature of soluble proteins following sonication.

In summary, the application of results generated from this research would lead to a number of practical benefits:

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