80-6 |
Mechanistic studies on the inactivation of microorganisms by high pressure |
S. BRUL1, A. J. M. Rommens2, and C. T. Verrips2. (1) Food Process & New Technologies, Unilever Research Vlaardingen/SILS Univ. of Amsterdam, Olivier van Noortlaan 120, Vlaardingen, 3133 AT, Netherlands, (2) Department of Molecular Cell Biology (now at Solvay Duphar), Utrecht University, Padualaan 8, Utrecht, 3584 CH High hydrostatic pressure processing is a technology that can be applied as a food preservation process. What the initial mechanism of microbial inactivation is, is currently still subject of many studies. In this presentation we will focus on lower eukaryotes and show that mild high pressure treatments, a typical example being 15 minutes 300 MPa at 25°C, leads to a change in cell wall protein structure of the yeast Saccharomyces cerevisiae such that cells are sensitised towards a treatment with b-1,3-glucanase. A deletion of specific cell wall proteins or an impaired biogenesis of cell wall oligosaccharides does not lead, however, to an increased sensitivity to the application of high pressure. In contrast, a deletion mutant with an impaired trehalose synthesis did show a 2 log increased inactivation compared to its parent strain when treated for 15 minutes with 200 MPa pressure at 25°C. It is well known that trehalose protects cellular membranes from heat induced damage. Indeed the disaccharide is essential for the initial cellular survival of heat stress. However, in the case of high hydrostatic pressure, plasma membrane related propidium iodide uptake did not correlate quantitatively with the observed decrease in colony-forming units. We concluded that the primary high-pressure inactivation step of yeast cells presumably involves a perturbation of (intracellular most likely mitochondrial) membranes. The fact that at sub-lethal pressure values the cell wall is perturbed in such a way that access of cell wall lytic enzymes is facilitated opens up the possibility of combined high pressure and cell wall lytic enzyme preservation treatments. Finally, we will indicate possibilities of combining high pressure treatment with the addition of membrane active antimicrobial peptides or naturally occurring lipophilic small organic molecules. The outlook will deal with the role of genomics in the study of the mechanism of high-pressure mediated microbial inactivation.
Session 80, Ultra high pressure: Molecular changes in foods
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