Journal
JOURNAL OF DAIRY SCIENCE
Volume 98, Issue 9, Pages 5890-5898Publisher
ELSEVIER SCIENCE INC
DOI: 10.3168/jds.2015-9410
Keywords
pulsed light; surface decontamination; spoilage and pathogenic bacteria; Cheddar cheese; process cheese
Funding
- Dairy Research Institute (Rosemont, IL) [DRI-65385]
- National Science Foundation MRSEC program [DMR-1120296]
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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 nonenteroliemorrhagic 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 microorganism's 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 x 5 cm slices, which were spot-inoculated with 100 mu L 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.
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