Gentle Preservation at 6,000 Bar

Consumers' expectations for food are constantly growing: They are to be natural, have an attractive appearance and keep for as long as possible. A maximum nutrient content is also a must. Innovations are constantly increasing safety and quality in the food sector. With innovative processes, such as those taking centre stage at Anuga FoodTec in Cologne, Germany, processing takes place gently and in fewer or shorter steps than with conventional technologies. Pulsed electric fields and UV radiation are examples of such gentle procedures.

Among the non-thermal pasteurisation techniques, high-pressure pasteurisation (HPP) is becoming increasingly important. Instead of heating the food over a longer period of time, it is briefly exposed to high pressure in order to destroy the harmful microorganisms. The process offers an interesting alternative to conventional heat treatment for sensitive products and follows the principles of the "clean label", i.e. food production without additives. With Hiperbaric, JBT and Thyssenkrupp Uhde, three key players in this technology were present at Anuga FoodTec 2024. And not without reason - because the process is revolutionising the way food and drinks are preserved and enabling manufacturers to create innovative products.

In high-pressure treatment, food is usually placed under high pressure in a water bath in its final packaging. In Japan, fruit jams have been treated with the HPP process since 1990 to ensure freshness and a longer shelf life. "This laid the foundation for the spread of high-pressure pasteurisation," says Boris Brockhaus from Uhde High Pressure Technologies. In the years that followed, HPP became a popular method of keeping food fresh without using heat or preservatives. "Since the start of the millennium, the process has been attracting increasing interest in the fruit and meat industry," says the Product Manager at HPP.

The food is placed in special baskets in the high-pressure container, which is guided into the machine and filled with water. A water pressure of 6,000 bar is applied evenly from all sides and reaches right into the core. Brockhaus says: "When the pressure is increased, the water is compressed by around 17 percent and an additional 60 litres of water are injected into a 350-litre high-pressure container to achieve the required pressure." As the water serves as a pressure-transferring medium, the packaged food is pressurised homogeneously and gently. No shearing forces are generated and the product is not deformed. The machine then opens and the goods are pushed outwards on belts so that they can be unloaded from the processing baskets. As the food is already in its final packaging, subsequent contamination can be ruled out. In addition, different products can be treated at the same time, such as fruit juices and purees within the same cycle.

At the Uhde Service Centre in Quakenbrück, Lower Saxony in Germany, a wide variety of foods such as juices, dairy products, meat products, seafood and many more can be processed. It is located in the immediate vicinity of the German Institute for Food Technology (DIL), with which Thyssenkrupp Uhde High Pressure Technologies co-operates in the field of research. Since 2021, up to 26 tonnes of food can be preserved gently and safely every day in a space of around 630 square metres. Among other things, the collaboration focuses on microbiological testing and the development of sustainable foods based on HPP technology.

In mid-June, participants of the "DIL Technology Day 2024" had the opportunity to visit the application centre. "Hygiene and safety in the food industry are more relevant than ever, and with HPP technology we are supporting the continuing trend towards the most natural, high-quality food possible," said Brockhaus, who led the tour. As high pressure eliminates many organisms that are harmful to food and can deactivate enzymes, decay processes are significantly slowed down and in some cases even prevented. For example, some types of fruit no longer turn brown. In contrast, flavourings and vitamins are not significantly damaged and remain intact. Brockhaus says: "High-pressure pasteurisation has proven particularly effective for fruit products and meat products. Although even very delicate foods are subjected to this pressure in their final packaging, their appearance and consistency remain largely unchanged after treatment."

Whilst the strength of the pressure is not high enough to break covalent bonds or create new bonds, it is able to destroy weak bonds. The cell membranes of bacteria and germs consist of precisely these weak bonds, which is why they are eliminated. "As the product can be treated directly in its final packaging, there is no subsequent contamination," says Brockhaus. The total aerobic bacterial count in freshly squeezed orange and peach juice is reduced many times over after just three minutes under pressure. The cycle time depends on the product and the resulting dwell time and can vary between two and nine minutes - depending on the pre-load, pH and water activity.

In terms of food safety, the process is just as safe as others - a conclusion that has also been confirmed by the European Food Safety Authority (EFSA) in a scientific expertise. The EFSA experts assessed whether the method can be used to control Listeria monocytogenes in ready-to-eat foods and as an alternative to thermal pasteurisation of raw milk. With certain time-pressure combinations, which are described in the expert opinion, the treatment method reduces the Listeria monocytogenes content in ready-to-eat foods. The following applies here: The longer the duration and intensity of the pressure, the greater the reduction. High-pressure treatment also proved to be effective in reducing the levels of other pathogens, such as Salmonella and Escherichia coli. For raw milk, experts have identified time-pressure combinations that can be considered just as effective as thermal pasteurisation.

And the process is also impressive in terms of energy efficiency, as Boris Brockhaus emphasises. This is because: "The total cycle has an energy consumption of around 17 kilowatt hours. In comparison, it would take almost twice as much energy to heat the equivalent amount of water from five to 80 degrees Celsius," says the expert.

High-pressure treatment can take place at various stages in the food chain and is generally used for pre-packaged products. It is suitable for raw products such as milk, fruit juices and smoothies, but also for pre-processed products such as products made from sliced cooked meat and ready-to-eat foods. In the latter case, it reduces contamination from the manufacturing environment, for example when cutting and handling the products. Dry products such as powder or products with an air content such as bread do not work, as the pressure in the product cannot be transferred or the air is pressed out of the product. The packaging itself must be flexible, such as PET bottles, vacuum bags, films, thermoformed trays or sleeves. Uhde High Pressure Technologies offers the opportunity to test the application at its Application Centre in Quakenbrück. As soon as the product has been developed to market maturity, UHPT provides support with contract processing. Customers can have their products processed at the Quakenbrück site up to a capacity of 25 tonnes per day.