Homogenisation is typically used to reduce the particle size of liquids to make them consistent.
Liquid milk is a prime example, where homogenisation is used to break up fat globules into small particles, leaving no cream layer at the top of the bottle or ‘watery looking’ milk at the bottom and creating a stable emulsion.
Reduced particle size increases the stability and longevity of the homogenised product and, in the example of a bottle of milk, once homogenised, the cream layer doesn’t separate out again.
Ultra high pressure homogenisation (UHPH) is an emerging technology that can be used for the simultaneous commercial sterility and stabilisation of pumpable food, cosmetics and pharmaceutical products.
The product is pre-heated up to 75°C then pumped through a pressure valve, where pressures of between 200MPa and 400MPa, depending on the type of product, are applied.
The temperature is increased at the valve but, as it is under pressure, heating time is very short and the product is at maximum temperature for only 0.2 seconds.
It is then pumped through various heat exchangers and cooled rapidly to below 26°C before being either hygienically or aseptically packaged.
While the technology is based on conventional homogenisers, advancements in valve design and materials mean that high pressures of up to 400 MPa can now be reached.
UHPH is a continuous process, unlike high pressure processing (HPP). There are some semi-continuous HPP units operating but the majority are batch processes.
In an HPP system, the product is packed prior to treatment, whereas UHPH involves a continuous liquid flow, so the treated product can be further processed prior to packaging.
Because the treated fluid reaches its maximum temperature for less than a second, the process avoids adverse thermal effects – such as cooked flavours and colours – which often result from traditional pasteurisation processes.
Overall, UHPH results in minimal thermal effects on nutritional value and sensory characteristics.
Studies of UHPH show that this technology can reduce particle size of fat globules and oil droplets to a greater extent than traditional homogenisation, which in turn can lead to improved stability of UHPH-treated beverages and foods.
In terms of food safety, pressures used in this emerging technology successfully inactivate microorganisms by rupturing cell walls through sudden pressure drops, shear stresses, cavitation and turbulence and also inactivate certain enzymes, leading to shelf-life extension benefits.
Recent research
Dr Anna Zamora of the Food Technology Plant Special Research Centre (CERPTA) at the Autonomous University of Barcelona, Spain, is one of the world’s primary researchers of UHPH.
Working on two projects funded through the EU and in partnership with English high pressure technology company Stansted Fluid Power, she and others have studied the effects of the technology on a variety of beverages.
Their research, which was presented at CSIRO’s International Nonthermal Food Processing Workshop in October 2012, shows some major advantages of UHPH over traditional homogenisation and pasteurisation processes.
The research shows that the microbiological organism count of non-dairy milks such as soy and almond milks treated at 300 MPa was nil (i.e. below the detection limit), similar to UHT-treated milk, with almost no heat effects.
Counts were similar in UHPH juice to pasteurised juice. In shelf-life studies, aseptically packaged products such as apple and orange juices kept their ‘fresh-like’ characteristics for more than three months at room temperature.
In milk, Zamora also showed that UHPH beverages showed less Maillard reaction, which can cause discolouration, and less whey protein denaturation and lactose effects, and retained better nutritional value compared to commercial pasteurised milk.
The research found that the particle size after treatment was considerably smaller at even the mildest UHPH conditions compared to conventionally treated samples, and therefore stability was considerably increased.
In fruit juices, UHPH inactivates enzymes such as pectin methyl esterase (PME), which promotes pulp separation in orange juice, and polyphenol oxidase (PPO), which promotes browning in apple juice.
Bioactive compound retention and antioxidant activity were similar between fresh and UHPH juices, and were both significantly higher than in pasteurised juices.
The researchers also undertook sensory analysis of UHPH products and ran product acceptance trials. The products tested were well received and perceived to be of a similar freshness as the raw products.
Food and UHPH
UHPH can also be used as an intermediate operation for manufactured products such as yoghurts and cheeses before packing or further processing, and also displayed the improved characteristics described above.
For example, milk can be treated by UHPH and then used to make cheese or yoghurt and these also exhibit characteristics of the UHPH process.
Zamora’s team found that UHPH not only affects the fat globules, but that the combination of homogenisation and pressure may also affect protein.
This can lead to increased gelation in products, making gels more homogenous and compact. For example, yoghurts made from high pressure homogenised milk are firmer, with less liquid separation during storage at cold temperatures.
This offers the processing advantage of not requiring the addition of skim milk powder to the formulation. The yoghurts were also lower in acidity.
UHPH cheeses exhibit a continuous and dense protein matrix with no serum pockets, unlike most other cheeses, giving an opportunity to develop restructured cheeses with different textural attributes and mouth-feel to those currently available.
Commercialisation
Ypsicon, a 2011 spin-off from CERPTA created to commercialise the technology, manufactures the UHPH system under patent. CERPTA uses 15L/hr and 100L/hr units, which are designed for product development, laboratories and food processing pilot plants.
Ypsicon, in collaboration with Stansted, is currently developing a 1000L/hr model and a complete UHPH line, including preconditioning and aseptic packaging, with high pressure resistant components for the food and beverage industries.
UHPH research is a relatively new field and
development only started in 2004. There aren’t any UHPH products on
the market yet, but based on the activity in Europe, it may not be
long before the first UHPH beverages and manufactured foods are on
the shelves.
UHPH versus HPP
UHPH differs from high pressure processing (HPP) because it is a dynamic pressure that uses sudden pressure drops, shear stresses, cavitation and turbulence to produce a pasteurised and homogenised liquid in one step.
HPP is a static pressure intervention that is applied simultaneously to all surfaces. It pasteurises but it doesn’t homogenise. In HPP, products – whether semi-solid or liquid – are pre-packed then treated.
Most
fruit juices and dairy products will require pasteurisation, so if
homogenisation is also required, UHPH can save a step in the
manufacturing line. It has also potential to reach higher throughputs
than HPP, and therefore may provide the potential to manufacture
products at larger scales.
About the author
Dr Pablo
Juliano is a process engineer and research scientist at CSIRO’s
food processing centre in Werribee, Victoria. He can be contacted on
03 9731 3276 or Pablo.Juliano@csiro.au.
