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24, chemin de Borde Rouge –Auzeville – CS52627
31326 Castanet Tolosan CEDEX - France

Dernière mise à jour : Mai 2018

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PhD thesis of Mariya Ignatova (2006-2009)

Combined effect of redox potential, pH and temperature on L. monocytogenes behaviour

In order to limit the presence of L. monocytogenes in foods, physico-chemical factors are widely studies and used in food processing. The redox potential (Eh) measures the redox state of environments (Jacob 1970). The impact of Eh on microbial physiology has been widely studied, but the results are often contradictory. Aiming at bringing greater knowledge on the effect of redox potential, the combined effect of Eh, pH and temperature on L. monocytogenes behaviour was studied. In a preliminary part of our work a bioreactor enabling stable redox measures was especially designed. The redox effect on growth, heat resistance and nisin sensitivity of L. monocytogenes was evaluated. Moreover a proteomic analysis was carried out to analyse the response of L. monocytogenes to a redox stress applied during growth and showed over- and under-expression of proteins involved in energetic metabolism, carbohydrates and proteins metabolism, DNA synthesis and repair. A moderate redox potential influence on growth was observed with an increased lag phase duration in reducing conditions. Reduced redox resulted also in decreased heat resistance at 58°C and a significant delay of regrowth. The unfavorable redox influence on the thermoresistance and growth of L. monocytogenes, notably in reducing conditions, might be exploited in improving food preservation methods.