In the last decade of 20th century, high pressure science and technique have found application in new areas: biology, biochemistry and production of novel foods. In Poland, the research on high pressure processing (HPP) of foods has been initiated in 1993 in the Institute of High Pressure Physics, Polish Academy of Sciences in cooperation with National Institute of Hygiene.

Effect of HPP on food and microbial contamination of food depends not only on pressure level, but also on time of exposure, temperature, pH and chemical composition of processed products. Vegetative forms of microorganisms are more susceptible to high pressure than microbial spores which may be destroyed only in the stage of germination.

High pressure pasteurization is an athermic technology of microbiological decontamination. While destructing microbiological agents it does not brake covalent bonds, neither primary structure of peptides. The influence of high pressure on cell systems includes changes in molar volume of elements. High pressure processed foods have longer shelf life without the risk of psychrophylic pathogenic bacteria growth.

The aim of the study was to define the impact of high pressure HPP on pathogenic bacteria including Listeria monocytogenes and Staphylococcus aureus in smoked vacuum packed fish – mackerel. Samples were subjected to various pressure levels: 200, 300, 400 and 500 MPa in a special high pressure chamber. The HPP was conducted in temperatures of 2°C or 40°C and the time of exposure was 5, 10 or 15 minutes. Number of bacteria was estimated after 2-4 hours following HPP and compared to control samples not subjected to HPP.

For each of the studied bacteria 42 HPP cycles were performed. The following results were obtained:

• Listeria monocytogens was more susceptible to HPP than Staphylococcus aureus irrespective of temperature,
• Listeria monocytogenes was completely inactivated at pressure level of 500 MPa in all samples of smoked fish irrespective of the time of HPP exposure,
• HPP is more effective against Stapylococcus aureus at the temperature of 2°C as compared to 40°C, and Listeria monocytogenes is more susceptible to HPP at 40°C.
• Pressure of 200 MPa does not have a significant effect on the number of Staphylococcus aureus bacteria.

Acknowledgments

The work was performed within a research project MNiI PO6T 006.29, 2005-2008.

References

1. [FAO] Food and Agriculture Organization 1999 May, Report of the FAO expert consultation on the trade impact of Listeria in fish products. Rome: FAO.FAO Fisheries Report nr 604, 34p
2. ArabasJ., J. Szczepek, L. Dmowski, V. Heinz, M. Fonberg-Broczek: New technique for kinetic studies of pressure-temperature induced changes of biological materialsAdvances in High Pressure Bioscience and Biotechnology, ed. by H. Ludwig, Springer-Verlag, 1999, p.537-540

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