Microbial inactivation by high pressure homogenization (HPH) was studied in two very different disruption chambers, one based on a piston micrometric valve and the other on an orifice valve, in order to relate the geometrical and fluid dynamics aspects with the rate of death of Escherichia coli, Lactobacillus delbrueckii and Saccharomyces cerevisiae. The kinetics of inactivation, obtained for multiple HPH passes at pressures ranging between 100 and 300 MPa, showed that the piston valve system is always significantly more efficient, probably due to the direct mechanical interaction of cells with the valve, being the characteristic dimension of the piston valve (3-14 gm) comparable to cell size and significantly smaller than the orifice valve (diameter of 130 mu m), as well as due to the higher extent of cavitation. In addition, an empirical Weibull inactivation model was successfully applied to fitting the experimental inactivation data of all tested microorganisms. (C) 2012 Elsevier Ltd. All rights reserved.