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Propidium monoazide coupled to real time PCR (PMA-qPCR) is a novel methodology proposed for the quantification of viable bacteria in food after microbial inactivation treatments. The aim of this work was to assess the effectiveness of different pressure levels on the lethality of a pool of Escherichia coli O157 strains in beef burgers by plate count and PMA-qPCR using uidA as target gene. Also, the effect on native microbiota counts, E. coli O157 counts, and physiochemical parameters of beef burgers during storage in refrigeration and frozen conditions were assessed. The treatment at 600 MPa for 5 min was the most lethal and was selected for the evaluation of bacteria behavior under storage conditions. Native microbiota and E. coli O157 were not recovered during refrigerated and frozen storage (4°C for 7 days and -18°C for 35 days). Cooking weight loss, pH, chromatic parameters, and texture were affected by HPP. PRACTICAL APPLICATION: Practical Application: PMA-qPCR can be used as an alternative to assess microbial inactivation by different high pressure processing (HPP) conditions (pressure level, holding time and temperature) more rapidly than conventional plate counts. In addition, it has the benefit of being able to quantify viable but nonculturable bacteria from contaminated beef burgers after HPP. Moreover, this novel technique generates less pathogenic residues, which minimizes workers' exposure to human biohazards.
Rey et al. (Mon,) studied this question.