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Hélène Simonin

Univ. Bourgogne Franche-Comté, AgroSup Dijon, PAM UMR A 02.102, Dijon, France

Are bacterial spores activated by High Pressure treatment at 20°C ?

Bacterial spores are extremely resistant life forms that play an important role in food spoilage and foodborne disease. The return of spores to a vegetative cell state is a three-steps process, these being activation, germination and emergence. High Pressure (HP) Process at mild temperatures (<50°C) is known to initiate the germination of a part of a spore population. In a preliminary work, we demonstrated that HP at 20°C also induces reversible sensitization of spores to the antibacterial peptide nisin without germination induction.

The objective of the present work is to investigate the nature of reversible and irreversible spore modifications induced by HP using Infra-red facilities in synchrotron Soleil. The changes of biochemical signatures of spore structures (lipids, proteins) were investigated both in situ and after HP treatments.

Our results showed that spores treated by HP at 50 °C and germinated spores had similar spectral signatures involving same structural properties. However, after HP performed at 20 °C, two groups of spores were distinguished; one of these groups was clearly identified as germinated spores. The second group displayed a unique spectral signature, with shifts in the spectral bands corresponding to changes in membrane fluidity. Besides, spores spectra in the amid region could be divided in several groups close to spectra properties of dormant, germinated or inactivated spores. The major contributions to the spectral variation between HP 20°C spores and other populations are localized at wavenumber corresponding to ????-helix and ????-structures. These changes in the lipid and in the amid regions could be the signature of reversible changes linked to spore activation.

This study shows for the first time reversible spore modifications by HP that could be used to design new sterilization processes.

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