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|Title: ||In-Package Heat Pasteurization Combined with Biocide-Impregnated Packaging Films for Inhibition of Escherichia coli 0157:H7 and Campylobacter jejuni.|
|Authors: ||Hughes-Hollar, LaVonda Ann|
|Advisors: ||Patricia A. Curtis, Committee Co-Chair|
Sophia Kathariou, Committee Member
Geraldine Luginbuhl, Committee Member
Paul L. Dawson, Committee Member
Brian W. Sheldon, Committee Co-Chair
Escherichia coli 0157:H7
|Issue Date: ||5-Nov-2003|
|Discipline: ||Food Science|
|Abstract: ||Even with HACCP food safety programs in place, millions of pounds of ready-to-eat food products are recalled annually due to product recontamination after cooking and prior to packaging. As a consequence of this risk of contamination, numerous cases of foodborne illness occur yearly. Food processors are extremely interested in identifying and implementing additional food safety critical control points during and following packaging operations that would ensure that consumers receive products that are of high quality and that are safe.
The first objective of this study was to generate and evaluate the thermal inactivation and lethality kinetics of E. coli O157:H7 and C. jejuni inoculated on the surface of vacuumpackaged, low-fat turkey bologna slices. This investigation included determining decimal reduction times (D-values) and ZD-values, activation energies, and rates of inactivation for these two pathogens. Packaged samples were submerged in a pre-heated water bath at temperatures of 55°, 60°, 65°, 70°, and 75°C or 53°, 55°, 60° and 62°C for E. coli O157:H7 and C. jejuni, respectively. The corresponding D-values calculated from survivor plots for E. coli O157:H7 were 289.5, 45.8, 15.8, 11.9 and 9.1 seconds, respectively (zD-value = 13.9°C). D-values for C. jejuni at 53°, 55°, 60°, and 62°C were 272.0, 192.1, 38.4, and 25.2 seconds, respectively (zD-value = 8.3°C). These findings indicate that C. jejuni has greater temperature dependence (i.e., more heat sensitive) than E. coli O157:H7.
The second objective of this study was to examine the inhibitory activity of a wheat gluten (70% w/w) and glycerol (30% w/w)-based film containing 500 μg/ml nisin as Nisaplin, 3% citric acid, 5 mM EDTA, and 0.50% Tween 80 (Film+N) against E. coli O157:H7 and C. jejuni suspended in 0.1% peptone water. Alternatively, a control wheat gluten and glycerol-based film (Film) lacking nisin and the other treatment components and a 0.1% peptone water suspension without any films (Control) were tested. While the E. coli O157:H7 population increased 3-logs over the 72 hour exposure period (~23°C) for the Control and Film treatments, the Film+N treatment population decreased by 2-logs (a 5.6 to 7.4 log reduction). In contrast, C. jejuni populations decreased to below the minimum detectable level (log 1.2 cfu/ml) after 24h exposure to all three treatments. However, C. jejuni populations exposed to the Film+N treatment died at approximately twice the rate as the other two treatments.
Information gleamed from the previous two studies was used in designing a third study where inoculated bologna samples were subjected to a minimal in-package pasteurization process (≤1-log reduction) combined with the inhibitory films. A heat treatment of 60°C for 60 seconds was initially applied to the inoculated and vacuumpackaged bologna and film treatments and then stored at 4°C for 7 days. A duplicate study involving only E. coli O157:H7 was also conducted but the storage time was extended to 5 weeks. Minimal reductions in E. coli O157:H7 populations of 1.0, 0.5, and 0.35 log cfu/ml were detected across the Control, Film and Film+N treatments, respectively, following the seven day storage/exposure period. Following the extended five week refrigerated storage period, the E. coli O157:H7 populations declined by 1.74, 1.14 and 0.27 log cfu/ml, respectively. For C. jejuni, population reductions of log 1.51, 2.11, 2.68 cfu/ml were detected for the Control, Film and Film+N, respectively, following the 7-day refrigerated storage period.
The findings of this study demonstrate that wheat gluten and glycerol packaging films containing nisin, chelators and a surfactant are more inhibitory against bacterial pathogens when suspended in a liquid system as opposed to contact with a relatively dry ready-to-eat food (bologna). The loss of inhibitory activity in the combined in-package pasteurization and film treatment may be related to a lack of product moisture necessary to facilitate extraction and migration of the treatment components to the food surface. The ultimate goal of this line of investigation is to develop a modified inhibitory packaging film that would prove useful as one of several food safety .hurdles. that collectively might contribute to producing safer and higher quality food products having extended shelf lives.|
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