80-5 |
Compression heating of food materials during high pressure processing |
V. M. BALASUBRAMANIAM, National Center for Food Safety & Technology, Illinois Institute of Technology, Moffett Campus, 6502 S. Archer Road, Summit-Argo, IL 60501 During high pressure processing (HPP), the temperature of a material increases as a result of compression. This thermodynamic compression heating behavior of the material is very predictable. This provides a unique opportunity to uniformly increase the product temperature with minimal thermal degradation effects. Sample temperature increases with pressure and decreases with pressure release. The magnitude of this change depends mainly on the compressibility of the substance, thermal property, initial temperature, and target pressure. The apparent temperature rise of a product processed in a pressure vessel is also influenced by rate of heat loss to the pressure medium and surroundings. Gases experience significant compression heating. In contrast, liquids are far less compressible than gases, and solids have the least compressibility. For example, the temperature of water increases 2-3°C per 100 MPa. The properties of water under pressure have been well characterized. Since water is a main ingredient of most foods, the compression of most foods exhibits temperature changes very similar to that of water itself. To date, water seems to be the slowest heating component under pressure and fats seem to have highest compression heating (up to 5-9°C per 100 MPa). Changes in product or pressurization medium temperature due to compression heating and subsequent heat transfer should be considered during HPP. These temperature changes can influence microbiological inactivation studies in foods of different composition, especially those involving bacterial spores.
Session 80, Ultra high pressure: Molecular changes in foods
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