Resistance and Membrane Fluidity of Endospores of Clostridium spp. During Pressure-Assisted Thermal Processing in the Presence of Antimicrobials

  • Author / Creator
    Hofstetter, Simmon C
  • Endospores of Clostridium spp. pose an economic threat to the food industry and put consumers at risk of foodborne illness. An increase in consumer demand for minimally-processed, ready-to-eat products has driven research to examine ways to mitigate current thermal processing severity used to inactivate endospores, while maintaining food safety. Pressure-assisted thermal sterilization (PATS) in combination with antimicrobial compounds is a promising technology. The first objective of this study was to determine the resistance of endospores of Clostridium spp. to the antimicrobials nisin and reutericyclin during PATS. Nisin and reutericyclin target cell membranes, are effective against endospores, and have a unique mode of action. The presence of nisin enhanced inactivation of endospores during thermal treatments, whereas reutericyclin had no effect. The presence of nisin and reutericyclin enhanced inactivation of endospores during early stages of PATS. However, the presence of reutericyclin appeared to facilitate survival of endospores. Resistance to nisin and reutericyclin during thermal treatment and PATS is species-dependent. The second objective of this study was to determine the composition of the inner membrane of endospores of Clostridium spp., and to assess membrane fluidity in situ and ex situ of thermal and high pressure / thermal treatment. Measurements of membrane fluidity may provide information to help explain species-dependent resistance of endospores to nisin and reutericyclin. The inner membrane of endospores was chosen as a target because of its barrier properties. Inner membranes of endospores of Clostridium spp. differed significantly in short chain:long chain fatty acid ratios, and saturated:unsaturated fatty acid ratios between species. The fluorescent probe LAURDAN was used to label and measure fluidity of the inner membranes of endospore populations. Labeling inner membranes of endospores with LAURDAN did not affect the viability or structure. Fluorescence measurements were done in situ and ex situ of thermal and high pressure / thermal treatment. At ambient conditions, the inner membranes of endospores of Clostridium spp. were in an ordered state indicative of a gel-phase membrane. The presence of reutericyclin during thermal treatments disrupted the gel-phase membranes. Conversely, the presence of nisin during high pressure/thermal treatments stabilized the ordered state of inner membranes of endospores.

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  • Degree
    Doctor of Philosophy
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