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RESEARCH PRODUCT

Understanding of the phenomena involved in the inactivation of bacterial spores by a process combining high pressure and heat treatment

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High Pressure Processing (HPP) is an established food processing technique for maintaining food quality while inactivating vegetative forms of pathogenic and spoilage bacteria. However, bacterial spores are very resistant to pressure, which requires the development of a strategy combining HPP with another modality (pressure cycling, heat treatment) to increase spore destruction. Currently, the combination of these processes are not implemented at an industrial scale due to the technically complex implementation and uncertain results given the diverse and contradictory literature on the level and mechanisms of spore inactivation by HP. The elucidation of spore inactivation mechanisms by pressure is therefore essential to assess the real potential of the industrial application of the HP process for the inactivation of bacterial spores. In the first chapter, special attention was paid to the pressure cycling process, which could improve spore inactivation by accelerating spore germination. The comparison with continuous HP treatment allowed to understand the effect of each parameter of the cyclicing modality on spore inactivation, and then to propose a pressure inactivation model. In the second chapter, exploitation of intrinsic properties and the use of extrinsic markers allowed the monitoring of the physiological state of pressure treated spores, and thus to highlight membrane alterations very different from that observed for a simple heat treatment. In the third chapter, a method using fluorescence lifetime imaging microscopy (FLIM) of a viscosity sensitive fluorophore was developped to study spore membrane perturbation by pressure. It showed a variation in fluorescence lifetimes, suggesting a variation in membrane viscosity following treatment at different pressure and/or temperature scales. Overall, these research works reinforce the understanding of spore inactivation mechanisms by HPP, while proposing ways to optimize the industrial application of the studied process.