title: Inactivation of Pseudomonas fluorescens in skim milk by combinations of pulsed electric fields and organic acids.
abstract: Pseudomonas fluorescens suspended in skim milk was inactivated by application of pulsed electric fields (PEF) either alone or in combination with acetic or propionic acid. The initial concentration of microorganisms ranged from 10(5) to 10(6) CFU/ml. Addition of acetic acid and propionic acid to skim milk inactivated 0.24 and 0.48 log CFU/ml P. fluorescens, respectively. Sets of 10, 20, and 30 pulses were applied to the skim milk using exponentially decaying pulses with pulse lengths of 2 micros and pulse frequencies of 3 Hz. Treatment temperature was maintained between 16 and 20 degrees C. In the absence of organic acids, PEF treatment of skim milk at field intensities of 31 and 38 kV/cm reduced P. fluorescens populations by 1.0 to 1.8 and by 1.2 to 1.9 log CFU/ml, respectively. Additions of acetic and propionic acid to the skim milk in a pH range of 5.0 to 5.3 and PEF treatment at 31, 33, and 34 kV/cm, and 36, 37, and 38 kV/cm reduced the population of P. fluorescens by 1.4 and 1.8 log CFU/ml, respectively. No synergistic effect resulted from the combination of PEF with acetic or propionic acid.
authors.affiliation: Department of Biological Systems Engineering, Washington State University, Pullman, Washington 99164-6120, USA.
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Fernández-Molina
authors.forename: Bilge
authors.initials: B
authors.lastname: Altunakar
authors.forename: Daniela
authors.initials: D
authors.lastname: Bermúdez-Aguirre
authors.forename: Barry G
authors.initials: BG
authors.lastname: Swanson
authors.forename: Gustavo V
authors.initials: GV
authors.lastname: Barbosa-Cánovas
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology*; D000818:Animals; D015169:Colony Count, Microbial; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004558:Electric Stimulation / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods; D006863:Hydrogen-Ion Concentration; D008892:Milk / Q000382:microbiology*; D011422:Propionates / Q000494:pharmacology*; D011551:Pseudomonas fluorescens / Q000187:drug effects / Q000254:growth & development*
chemical_list: D011422:Propionates; C029658:propionic acid; D019342:Acetic Acid