Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Study of safety related aspects during HPLT processing

The inactivation of Bacillus subtilis strain PS832, grown in TSB as culture medium, was studied for different pressure, temperature and time combinations. Some of these combinations lead to solid-solid phase transitions after freezing at atmospheric pressure and subsequent pressurisation.

Depending on the pressure level, the samples may undergo solid-solid phase transitions from ice I into the domains of ice II, ice III or ice V. Treatments of cells between 250 and 350 MPa at -25°C are the most effective in inactivating vegetative Bacillus subtilis cells. For these conditions, a double effect of extracellular solid-solid (Ice I-III) phase transition and possible intracellular solid-liquid phase transition is suggested to be key in mediating the observed drop in viability. The damages on Bacillus subtilis PS832 vegetative cells induced by subzero temperatures and pressures up to 250MPa in buffer solution was studied by means of flowcytometry with combination of membrane permeability and viability probes such as PI and cFDA.

The growth of single cells was traced by measuring the optical density and light scatter of the growth medium. Bacterial cells showed a heterogeneous resistance to the HPLT treatment. The synergistic effects of low high pressure processing, subzero temperature and pH was investigated on Listeria monocytogenes cells in buffer and in smoke salmon marinated. Various conditions of pressure (100, 150 and 200 MPa) at subzero temperature (-10, -14 and -18°C) were applied without freezing due to the phase diagram of water under pressure. Selected pH acid (4.5) and neutral were considered.

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