Pressure change technology

Pressure change technology (PCT) is a non-thermal and non-chemical process for treating liquids with suspended microorganisms.

 

Principle

This method – also known as “cold pasteurization” – is mainly used between 5 °C and 40 °C at pressures of up to approx. 50 MPa. The liquid or suspension to be treated as well as the working gas (e.g. argon or nitrogen) are each placed under working pressure and then mixed homogeneously. In the case of microorganisms with cell membranes the gas diffuses through the membrane into the cells until the cytoplasm is saturated with gas. When subsequently the mixture is abruptly brought down to ambient pressure, the gas resumes its original gaseous state of aggregation and expands. This process destroys the cells eruptively. Cavitation effects may also result in damage to particle surfaces.

PCT pilot plant for contract application studies

© Fraunhofer IGB
Research facility for the purpose of testing PCT technology under strict hygienic conditions.

On the basis of years of research and project work, Fraunhofer IGB experts have built a PCT testing facility in which they can investigate the process for the stabilization and preservation of any liquid products and can determine the optimum parameters in each individual case.

  • Located in a cleanroom technical center (Class E cleanroom)
  • Continuous treatment of up to 4 L/min

Additionally, for basic testing – for example, at a customer’s location – a flexibly configurable and mobile PCT lab plant is currently being constructed.

Applications

  • Preservation of liquids by inactivation of microorganisms and enzymes (“cold pasteurization”)
  • Stabilization of alcoholic and non-alcoholic beverages, dairy products, plant-based extracts
  • Stabilization of suspensions or liquid preparations for pharmaceutical and cosmetic applications
  • Gentle cell disruption to obtain intracellular productsRelease of high-quality, thermolabile components from plant-based, animal or microbial cells

Advantages

  • Component-friendly preservation without chemical additives
  • Flavors, aromas and nutritional-physiological properties are not impaired in the preservation of liquid foodstuffs.
  • Protection from oxidation by using inert process gases
  • Can be applied flexibly in the process
  • Inactivation of oxidative enzymes (polyphenoloxidase, peroxidase)
  • Extraction and/or recovery of valuable cellular components under mild conditions
  • Environmentally friendly – no chemicals used, recovery of the process gas
  • Energy-efficient

Example: Preservation of liquid foods

At the Fraunhofer IGB we are further developing pressure change technology for the preservation of liquid foodstuffs such as fruit juices or wine. The aim of a current project for the stabilization of wine without preservatives is the inactivation of microorganisms participating in the fermentation process. The use of inert process gases such as argon or nitrogen prevents the oxidation of sensitive components. This method was first of all realized and validated as a batch process: parameters such as temperature, retention time, gas type and the effect on the microorganisms involved (yeasts, lactic acid bacteria), and also physical-chemical and sensory properties of the product are investigated. At present we are demonstrating the technology in a mobile plant under real conditions at the end-users’ facilities.

Example: Cell disruption for biotechnological processing

Pressure change technology is also suited to disrupting plant-based or microbial cells to extract intracellular metabolites. Thus we have been able to demonstrate the disruption of microalgae cells using PCT in order to extract superior-quality components for food supplements or cosmetics. For example, combining the PCT process with high-pressure extraction and the use of various process gases, omega-3 fatty acids can be extracted with greater energy efficiency than previously.