From Top Wiki
PATS, also known as Pressure Assisted Thermal Sterilisation or HPP-sterilisation (High Pressure Processing Sterilisation) is a preservation technique for food. It uses a combined effect of high temperature and high pressure.
Figure 1 Process flow in PATS/HPP sterilisation
In preserving by high pressure, the product is heated by adiabatic heating (3-5 °C per 100 MPa). In PATS or HPP-sterilisation, this adiabatic heating effect is used maximally to heat preheated products to sterilisation temperature. This heating process is fast and uniform.
The product is filled into the packaging and sealed to close (Figure 1). Then the product is preheated to 70-80 °C in a continuous heater (in-line) or by using volumetric heating (eg microwave or RF). Volumetric heating goes faster than heating from outside, resulting in better product quality. After preheating, the product is placed into a warmed pressure vessel. In the vessel, pressures of 600 – 800 MPa can be reached. The product is kept under this pressure for about 3 minutes. The temperature increases to 95-115 °C due to the adiabatic heating. Part of the adiabatic heat is lost to the pressure vessel, which is cooler than the product (~70 °C vessel, product 95-115 °C). Due to this temperature difference, it cannot be guaranteed that the sterilisation process reaches the desired parameters. As soon as the pressure is released from the vessel, the temperature decreases to start temperature. After the high pressure treatment, the product is cooled.
PATS or HPP-sterilisation is a batch process, in which the packaged product is treated. The added value lies mostly in products as ready-to-eat meals, thick sauces and soups (with particles). Product quality
Figure 2 Effect of preservation methods on aroma components in fresh basil
Preservation of a product by PATS/HPP sterilisation influences the presence of micro-organisms, enzymes, flavour, texture and the vitamin content.
- The inactivation of enzymes by PATS/HPP sterilisation depends on several factors, like the type of enzyme, pressure, process time, pH-value and temperature
- PATS can be used to inactivate vegetative cells of micro-organisms, mould spores and bacterial endospores.
- The product flavour is retained better by sterilisation by PATS than by sterilisation with other techniques (see PHPP in figure 2).
- PATS/HPP sterilisation affects the texture of the product. This is caused by the prewarming, the high temperature achieved during the pressure treatment and by the pressure itself. Vegetables and fruit can turn soft. Proteins are denaturated by a pressure of 300 MPa, giving meat and fish a cooked appearance. The texture on the other hand resembles the texture of raw meat.
- The vitamin loss greatly depends on the product that is being treated. In spinach the vitamin C is retained after a PATS/HPP sterilisation treatment, while in apple juice the loss is about 25%.
Advantages and disadvantages
- No risk for contamination during filling (the product is treated in its packaging)
- Fresh properties are better preserved than with current sterilisation methods
- The technique can be used for many product shapes and volumes
- Instantaneous, homogenous heating
- Short process time
- Less energy input necessary than for sterilisation in an autoclave
- Price per product is relatively high
- New technique
- Not suitable for all packaging materials (tin cans and glass not possible)
- Batch process
- A slow heating and cooling process can undo the advantages of a fast PATS/HPP sterilisation process
- Problems with heat loss to the pressure vessel have not been solved yet
- Equipment not yet available on commercial scale
There are no PATS systems on a commercial scale available yet. The following equipment suppliers are working on the development:
- Avure: 100, 215 en 350 litre pressure vessels; maximum pressure 600 MPa
- NC Hyperbaric: horizontal vessels starting at 55 litres, maximum pressure 600 MPa
Investment and running costs
There is no commercial equipment on the market yet. This makes it difficult to estimate the investment and running costs. The total investment for a HPP-unit and preheating are estimated at €1.400.000,-. The total running consts are estimated at €0.15/kg.
- You can view here a lecture on PATS by Wouter de Heij.
- Wouter has written a blog article (in Dutch) on PATS on his personal blog earlier here.
- Some slides at slide share, posted by Wouter de Heij (early 2012).