title: Pulsed-light inactivation of pathogenic and spoilage bacteria on cheese surface.
abstract: Cheese products are susceptible to postprocessing cross-contamination by bacterial surface contamination during slicing, handling, or packaging, which can lead to food safety issues and significant losses due to spoilage. This study examined the effectiveness of pulsed-light (PL) treatment on the inactivation of the spoilage microorganism Pseudomonas fluorescens, the nonenterohemorrhagic Escherichia coli ATCC 25922 (nonpathogenic surrogate of Escherichia coli O157:H7), and Listeria innocua (nonpathogenic surrogate of Listeria monocytogenes) on cheese surface. The effects of inoculum level and cheese surface topography and the presence of clear polyethylene packaging were evaluated in a full factorial experimental design. The challenge microorganisms were grown to early stationary phase and subsequently diluted to reach initial inoculum levels of either 5 or 7 log cfu/slice. White Cheddar and process cheeses were cut into 2.5×5 cm slices, which were spot-inoculated with 100 µL of bacterial suspension. Inoculated cheese samples were exposed to PL doses of 1.02 to 12.29 J/cm(2). Recovered survivors were enumerated by standard plate counting or the most probable number technique, as appropriate. The PL treatments were performed in triplicate and data were analyzed using a general linear model. Listeria innocua was the least sensitive to PL treatment, with a maximum inactivation level of 3.37±0.2 log, followed by P. fluorescens, with a maximum inactivation of 3.74±0.8 log. Escherichia coli was the most sensitive to PL, with a maximum reduction of 5.41±0.1 log. All PL inactivation curves were nonlinear, and inactivation reached a plateau after 3 pulses (3.07 J/cm(2)). The PL treatments through UV-transparent packaging and without packaging consistently resulted in similar inactivation levels. This study demonstrates that PL has strong potential for decontamination of the cheese surface.
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853.
authors.forename: J
authors.initials: J
authors.lastname: Proulx
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853.
authors.forename: L C
authors.initials: LC
authors.lastname: Hsu
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853.
authors.forename: B M
authors.initials: BM
authors.lastname: Miller
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853.
authors.forename: G
authors.initials: G
authors.lastname: Sullivan
authors.affiliation: Department of Food Science and Agricultural Chemistry, McGill University, Ste Anne de Bellevue, Québec, H9X 3V9, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Paradis
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853. Electronic address: cim24@cornell.edu.
authors.forename: C I
authors.initials: CI
authors.lastname: Moraru
mesh_terms: D000818:Animals; D002611:Cheese / Q000382:microbiology*; D015169:Colony Count, Microbial; D003666:Decontamination / Q000379:methods; D004305:Dose-Response Relationship, Drug; D019453:Escherichia coli O157 / Q000302:isolation & purification / Q000528:radiation effects; D005506:Food Contamination; D005516:Food Microbiology; D018857:Food Packaging; D008027:Light; D008087:Listeria / Q000302:isolation & purification / Q000528:radiation effects; D008089:Listeria monocytogenes / Q000302:isolation & purification / Q000528:radiation effects; D020959:Polyethylene / Q000737:chemistry
chemical_list: D020959:Polyethylene
keywords: Cheddar cheese; process cheese; pulsed light; spoilage and pathogenic bacteria; surface decontamination