Controlling Microbial Contamination in Packaged Foods by Post Packaging UV-C Light Treatment
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The ability of Ultraviolet-C (UV-C) light to penetrate through plastic packages and to reduce E. coli or other microbes on the surface of foodstuffs such as beef bologna and English cucumber packaged in in plastic films was investigated in this study. The transmission of UV-C light through several plastic films used commercially in food packaging was measured. Effects of UV-C light treatment on both of food quality and films properties were investigated. PE film had the highest measured UV-C light transparency among the 15 films tested, at 76%, followed by PP and OPP films, with 59 and 57%, respectively. Exposure of PE film inoculated with E. coli k-12 with UV-C light resulted in a 4.6 log CFU/ml reduction after a dose of 164 mJ/cm² was applied. Reduction of E. coli k-12 on inoculated bologna packaged in PE film was higher (1.48 log CFU/g) compared to the other films (OPP and ClearTite®) following treatment with 406 mJ/cm2 of UV-C. Inoculated packaged cucumber treated at 23 0C for six min with UV-C (560mJ/cm2) resulted in a 1.60 log CFU/g reduction. UV-C light treatment delayed the loss of firmness and yellowing of English cucumber up to 28 day at 5 0C. Electron microscopy images show that UV-C light treatment influences the morphology of the E. coli cells. The surface-free energy of films was used as an indicator for changes to film surface properties. UV-C light exposure (560mJ/cm2) of PE, OPP and ClearTite® films at doses in this study had no significant effect (P≥0.05) on the surface properties of the treated films, water vapor transmission rate (WVTR), or oxygen transmission rate (OTR) of the PE film used to package the cucumbers. This study demonstrated that treating ready-to-eat meats such as a bologna with UV-C light after packaging can reduce E. coli populations by a 1.5 log cycle without negatively affecting the surface properties of plastic films. In addition, treating cucumbers with UV-C light following packaging in PE film can reduce bacterial populations and delay quality loss making this procedure may be appropriate for other similarly packaged fresh fruits and vegetables.