Ultrasound technology can be used to skim the fat from milk

We wanted a blue-sky project that was academically challenging and with potential marketability.

Milk is such an everyday part of our lives that it’s easy to forget its other role, as a quiet, consistent achiever in the Australian economy. Last year we produced 9480 million litres of it, and in the year to June 2013 we exported $2.76bn in milk and milk products, nearly 10 per cent of the world’s export market.

The Australian dairy industry is innovative and always on the lookout for better ways of doing things, which is why a team from Swinburne, in conjunction with CSIRO, is now examining milk with a particular question in mind – how can we use ultrasonic waves to skim milk? Their pioneering work is revealing some of milk’s deepest secrets.

Reinventing the wheel

Skimming – or separation of the fat – is the key component of milk processing, as old as farming itself. For thousands of years it was a simple matter of leaving the milk to rest in a cool corner while gravity did its work. When the centrifuge took over about 150 years ago, it paved the way for large-scale industrialised processing.

Skimming allows a standardised product, as the fat can be added back in exactly the desired quantity.

The ultrasound project originated with the Gardiner Foundation, a philanthropic organisation dedicated to dairy industry research, which approached the CSIRO to evaluate different skimming technologies. “We wanted a blue-sky project that was academically challenging and with potential marketability,” says Dr Aaron Gosling, the Foundation’s program manager, innovation.

Working in collaboration

The CSIRO, itself a leader in the use of ultrasonics for food processing, contacted Swinburne because of the established reputation of its ultrasonics group, of which Associate Professor Richard Manasseh is a key member. “Richard was excited when we contacted him,” recalls Dr Pablo Juliano, research scientist at the CSIRO. With funding from ARC Linkage Projects, a three-year $1.2m research project was born, due to conclude in mid-2015.

What the project needed, Associate Professor Manasseh knew, was a multidisciplinary approach. His team includes bio-interface engineer, Professor Sally MacArthur, postdoctoral fellows Dr Linda Johansson and Dr Tom Leong, mathematician and PhD student Javeria Jalal, electrical and food process engineers from CSIRO, as well as dairy industry members. They’re needed to understand all the factors, from the complex colloidal system of milk to the many acoustic phenomena at play. “Richard is a very applied guy,” observes Dr Gosling, “He wants to make real change, not just perform research.”

The role of milk fat globules

The focus of everyone’s attention is the milk fat globule, and it’s turning out to be a very interesting entity.

“We already knew that when you introduce a sound wave through fluid it causes particles to cluster – it creates expansion and contraction causing the particles to collect in vertical bands a half-wavelength apart – but it hadn’t been tried on milk particles,” says Associate Professor Manasseh. “They are tiny – you could fit 50–100 on the width of a human hair – and are formed like biological cells in that they have a membrane.”

We’re sure to hear more about these membranes in the future. They’ve been found to contain potentially protective properties against diseases such as Alzheimer’s and breast cancer, with the smaller milk globule membranes of particular interest as a future nutraceutical, a naturally occurring food supplement that is thought to have a beneficial effect on human health. But first things first: right now, the research is about establishing the parameters and design for using ultrasound on milk, then taking it from benchtop to a scaleable prototype.

Applying the research

Dr Linda Johansson, whose background is in micro-fluidics, is studying the fat globules using Swinburne’s microscopy facilities, including micro PIV (micro particle imaging velocimetry). While observing how these particles aggregate or coalesce in the acoustic field, Dr Johansson keeps at the back of her mind the visits she’s made to real dairy plants and how her work could translate into useful ‘on the floor’ technology. “It’s being part of a project with ‘market pull’ that makes it so rewarding,” she says.

One of ultrasound’s benefits is the ability it gives to separate out fat globules by size. As small and large globules have different properties, imparting smoothness or creaminess, they can be separated to create better tastes and textures for new dairy products.

Dr Tom Leong, who recently completed his PhD in ultrasonics, is examining the optimal frequency for separation – too high a frequency and the ultrasound gets absorbed by the milk and doesn’t travel far enough for a result, too low and it creates cavitation, or the collapse of microscopic bubbles, which might break up the membranes. “The holy grail is to create something highly precise that will really add value, like a nutraceutical in the future,” he says, “But it’s easy to forget that not long ago knowing how to separate milk using ultrasound was the holy grail!”

The beneficiaries of their work in the short term will be smaller dairies, of which there are around 120 in Victoria, as well as specialist cheese producers, as ultrasound skimming is very gentle, making it ideal for traditional products such as parmesan. Also, if climate change means new dairies need to be built in new locations, they will have start-up access to this Australian technology. But with the project not due to end until 2015, and so many people working collaboratively with Swinburne’s team, it could still yield a number of surprises.

Boutique solutions

“It was a meeting of kindred minds,” says Yarra Valley Dairy cheesemaker Jack Holman, about the Swinburne ultrasonic milk team’s visit to the dairy in Yering, Victoria. “We’re both passionate about what we do, so there was a real buzz. And it was a learning experience for both sides.

“Careful separation of milk is critical,” he explains. “If you damage the fat or proteins it will also damage the texture, mouth feel and longevity of the product we make. So it’s great to see innovation on this – and their excitement.

“There are two potential advantages from ultrasonic separation,” he says. “Firstly, if it allows a real difference in gentleness of separation, we could create new products and be really inventive, leading to a market edge. The other advantage is practical. If the unit is small and relatively inexpensive, dairies like ours would be able to separate their own milk, providing a practical solution that isn’t available to them at the moment.”

More information, visit the Yarra Valley Dairy website.

Media enquiries