Without a specific treatment food and pharmaceutical products are exposed to contamination and spoilage. For food safety the contamination in food should be inactivated or removed. The food safety is realized normally by thermal processes, like pasteurisation or sterilisation (e.g. 121 °C, 15 minutes). The problems of these methods are the instability of heat sensible ingredients (vitamins or pharmaceutical active agents) and the reduction of them during the processes. New processes tend to use non - thermal preservation treatments such as magnetic or electrical fields, ionisation, light pulses, high hydrostatic pressure (p > 100 MPa) or ultrasound (Mertens & Knorr, 1992). Disadvantage of the most of these methods is a high energy consumption. The inactivation of microorganisms in food with the high static pressure technology has a high potential (Torres & Valezquez, 2005). The influence of high pressure of food ingredients is well known (Pfister & Dehne, 2001). Together with partners from industry and research establishments an innovative technology for reduction of microbial count in liquid foods and pharmaceuticals is developed and realised. The principle of this new technology is pressure change. In the first step the liquid is saturated with gas. As a result of diffusion the gas is transferred into cells. After a rapid expansion the cells are disrupted, because of expansion is faster then diffusion out of the cells. This technology operate in a range of pressure up to 50 MPa and at temperatures between 0 – 40 °C. It will be an alternative to thermal process technologies with the advantage of conservation of natural active substances and is a gentle process for inactivating microorganisms in food.

This new technology was applied to food relevant organisms. Influencing factors were investigated with help of physiological changes of P. fluorescence, L. brevis, S. cerevisiae and E. coli. The results of this study indicate that microorganisms can be reduced up to 7 log. The reduction of the cell number can be detected after a treatment of only 5 minutes. The treated cells show cellular membrane damage and a reduced viability. The success of this pressure change technology depends on the process parameters (temperature, pressure and kind of gas), the kind of microorganisms (structure of cell membrane) and the age of the cells. Results will be shown and discussed.

Keywords: pressure change technology, inactivation of microorganisms, microbiological safety of liquids