High hydrostatic pressure inactivation of Bacillus subtilis var. niger spores : the influence of the pressure build-up rate on the inactivation

In the context of the development of commercially applied high pressure processes it is necessary to evaluate the impact of high pressure on the inactivation of bacterial populations. From the results kinetic models should reliably predict inactivation under dynamic conditions. High pressure processes imply an initial phase of pressure build-up, accompanied by a temperature increase due to adiabatic heating. Since pressure application leads to the generation of heat, the question may arise whether this dynamic p-T profile will influence the spore inactivation. The come-up time (the time needed to reach the constant treatment conditions) is an important variable that needs to be considered in the design and optimization of high hydrostatic pressure processes due to its significant contribution to microbial inactivation. The pressure-temperature inactivation kinetics of Bacillus subtilis var. niger spores was first studied under isobaric-isothermal conditions in the pressure range 50�400 MPa at temperatures between 25�70°C. Isobaric-isothermal inactivation of spores appears to follow a fairly linear trend and can be described by a first order model. The kinetic parameters (kref, Ea and DV¹) were calculated at different pressure and temperature levels. Assuming first order kinetics for non-isobaric/non-isothermal inactivation of Bacillus subtilis spores during the come-up time, the integral effect of the inactivation process under dynamic conditions was quantified. To do that, the above mentioned kinetic parameters were used to calculate the inactivation constants as a function of temperature and pressure. The total come-up time was divided in time steps of one second and the inactivation constants were calculated for each seconds time interval. The experimental pressure build-up was carried out in two different ways: (a) fast � pressure was developed with the highest possible rate and the come-up time was between 118 and 677 seconds depending on the pressure level of the treatment; (b) slow � pressure was built-up with a rate of 20 MPa/min and the come-up time was between 180 and 1337 seconds. The inactivation effects during these come-up times after fast and slow pressure build-up processes were measured and compared with the calculated effects. The comparison reveals an additional inactivation effect on spores due to dynamics of fast pressure build-up. This is the first time that such an effect has unambiguously been shown.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Heidelberg

Year

2004

Author dc:creator

• Urzica, Anca Cristina

Contributors dc:contributor

• Ludwig, Horst

Repository record source_url

http://www.ub.uni-heidelberg.de/archiv/4930

OAI identifier oai:identifier

oai:archiv.ub.uni-heidelberg.de:4930