Bacterial spore inactivation by ultra-high pressure homogenization

A new generation of high pressure homogenizers reaching up to 400 MPa offers opportunities for spore inactivation and high pressure sterilization of foods. A Stansted Fluid Power ultra-high pressure homogenization (UHPH) unit was tested to inactivate bacterial spores in a model buffer system. Bacillus subtilis PS832 and Geobacillus stearothermophilus ATCC7953 spores’ thermal resistances were assessed (D, z-value and Ea). The pressure and valve temperature were monitored during UHPH. Residence times under pressure and high temperature were estimated and enabled comparison with thermal inactivation, indicating the estimated thermal contribution to inactivation. Spore germination was also assessed but no germination was observed. Up to five log10 B. subtilis and two log10 G. stearothermophilus spores were inactivated by the harshest treatments (> 300 MPa –Tvalve > 145 °C for ~ 0.24 s). The inactivation profiles were similar to the predicted thermal inactivation suggesting that the valve temperature might be a dominant parameter leading to bacterial spore inactivation. Industrial relevance This work showed the UHPH potential for spore inactivation and the need of highly thermoresistant surrogates for process validation, for instance, G. stearothermophilus ATCC7953 spores. Both these findings are highly relevant for industrial application as, to date, no surrogate for this process was suggested while the first patents for the technology transfer to industry are being issued.