Barotolerance of Acid-adapted and Cold-adapted Bacterial Isolates of E. coli O157:H7, Salmonella spp., and L. monocytogenes in an Acidic Buffer Model

Abstract

The fruit and vegetable juice industry has shown a growing trend in minimally processed juices. A frequent technology used in the production of functional juices is cold pressure, which refers to the application of high pressure processing (HPP) at low temperatures to inactivate foodborne pathogens. HPP juice manufacturers are required to demonstrate a 5-log reduction of the pertinent microorganism to comply with FDA Juice HACCP. However, there is no consensus on validation study approaches for bacterial strain selection or their preparation. Individual bacterial strains were grown using three different growth conditions: neutral, cold-adapted, and acid-adapted. Approximately 6.0-7.0 log CFU/mL of the matrix-adapted bacterial strains were inoculated individually into buffered peptone water (BPW) at pH 3.50 ± 0.10 (HCl adjusted) and treated at sublethal pressures of 500 MPa for Escherichia coli O157:H7 and 200 MPa for Salmonella spp. and Listeria monocytogenes (180 s, 4°C). Analyses were conducted at 0, 24, and 48 h (4°C storage) post-HPP on nonselective media. E. coli O157:H7 exhibited greater barotolerance than Salmonella spp. and L. monocytogenes. In neutral growth conditions, E. coli O157:H7 strain TW14359 demonstrated the greatest resistance (2.94 ± 0.64 log reduction), and E. coli O157:H7 strain SEA13B88 was significantly more sensitive (P < 0.05). Salmonella isolates, neutral and acid-adapted, expressed similar barotolerance to one another. Cold-adapted S. Cubana and S. Montevideo showed greater resistance compared to other cold-adapted strains. Acid-adapted L. monocytogenes strain MAD328 had <1.00 ± 0.23 log reduction while acid-adapted L. monocytogenes strains CDC and Scott A were significantly more sensitive (P < 0.05) with reductions of 2.13 ± 0.48 and 3.43 ± 0.50 log CFU/mL, respectively. These results suggested, under the conditions tested, bacterial strain and preparation methods influence HPP efficacy and should be considered when conducting validation studies.

Keywords: Acid adaptation; Cold adaptation; HPP validation; High-pressure processing; Juice HACCP; Pathogen inactivation.