title: pH and solute concentration of suspension media affect the outcome of high hydrostatic pressure treatment of Listeria monocytogenes.
abstract: The effect of pH and solute concentration of suspension media on high hydrostatic pressure (HHP) induced inactivation of Listeria monocytogenes (approximate 10(8) CFU/ml) was investigated by the using treatment between 300 MPa and 600 MPa at 25 degrees C for 10 min. The suspension media used in this study represented different concentrations (0.1% to 10%) of buffered peptone water (BPW) with an adjusted pH of 4 to 7. An increase in the concentration of BPW resulted in a decreased HHP-induced inactivation of L. monocytogenes that was dependent on the pH of the medium. HHP-treatment at 300 MPa showed no bactericidal effect at neutral pH regardless of the BPW concentration. When the pH of BPW (0.1% to 5%) was reduced to 4, L. monocytogenes was completely inactivated (more than an 8 log cycle reduction) with a HHP-treatment of at least 300 MPa. HHP-treatment above 400 MPa completely inactivated L. monocytogenes in a relatively dilute BPW (0.1% and 1%) with an adjusted pH below 6. While only a 2 log cycle reduction was observed in 10% BPW at the pH ranging from 5 to 7 after treatment with 600 MPa, L. monocytogenes in 10% BPW at pH 4 was completely inactivated. Even though a significant bactericidal effect of HHP-treatment was not observed when applied with a low pressure such as 300 MPa or suspended in higher BPW at neutral pH, a reduction of the pH greatly affected the HHP-induced inactivation of L. monocytogenes. These results indicated that information concerning the pH of food or media would greatly assist an optimization of HHP-treatment for the inactivation of bacteria.
authors.affiliation: Food Piezotechnology Laboratory, National Food Research Institute, 2-1-12, Kannondai, Tsukuba, Ibaraki 305-8642, Japan. koseki@affrc.go.jp <koseki@affrc.go.jp>
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Koseki
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry*; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D006874:Hydrostatic Pressure; D008089:Listeria monocytogenes / Q000254:growth & development*; D009994:Osmolar Concentration; D011237:Predictive Value of Tests; D013696:Temperature; D013997:Time Factors
chemical_list: D003470:Culture Media