54F-27 |
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S. E. WOODLING, Food Science, Cornell Univ., Stocking Hall, Ithaca, NY 14853 Pulsed Light (PL) has been proven successful in reducing microbial populations. Prior work has shown that the effectiveness of PL treatment can vary as a function of the substrate properties and the spatial distribution of the microbial load. In order for PL to be adopted by the food industry, the specific treatment parameters that impart microbial injury and destruction (i.e. spectral region), as well as the potential sources of treatment heterogeneity must be elucidated. Stainless steel coupons (50 sq.cm) were inoculated with 1 mL of several different inoculum populations of Listeria innocua and treated with PL. Survivors were enumerated by both SPC and MPN procedures - the latter allowed identification of sublethally injured cells. To determine the contribution of various spectral ranges on PL inactivation, a series of optical filters were used. The data indicated an increasing trend in the level of reduction as the inoculum population increased, particularly for lower intensity treatments (R-squared = 0.84 for 3 pulses). The comparative SPC and MPN evaluation of survivors indicated that sublethal injury took place. After 9 and 12 pulse treatment of ~2e7 CFU/(50sq.cm) the SPC method indicated survivor counts < 2.5e3 CFU/(50sq.cm), yet MPN procedures consistently yielded counts of 1.1e5 CFU/(50sq.cm). The difference is due to the fact that some of the cells were sublethally injured and underwent repair and recovery under the MPN testing conditions. Data obtained using optical filters indicated negligible microbial reduction for the UVA-VIS-NIR spectral range. These results suggest that the major contributor to the lethality of PL lies within the 180nm-315nm range (UVC + UVB). The fact that PL results in high levels of sublethal injury can be used in a hurdle technology strategy, where the application of another method of decontamination immediately after the PL treatment could result in high levels of microbial reduction.
Session 54F, Nonthermal Processing: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |