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Behavior of E. Coli 0157:H7 in Packaged Spinach after Exposure to Sanitizing Solution
Title
Behavior of E. Coli 0157:H7 in Packaged Spinach after Exposure to Sanitizing Solution
Creator
Lu, Yin
Date
2011-12-13, 2011-12
Description
Leafy greens have been associated with multiple outbreaks of Escherichia coli O157:H7 (EC) infection in recent years. More information is...
Show moreLeafy greens have been associated with multiple outbreaks of Escherichia coli O157:H7 (EC) infection in recent years. More information is needed on EC survival during post-harvest processes, and our study aimed at evaluating survival in packaged spinach after treatment of cells with sodium hypochlorite. A green fluorescent protein-expressing strain of EC was exposed to sodium hypochlorite in two different ways, i.e., exposed in solution or on the spinach leaves. For exposure in the solution, EC was inoculated into 1 ppm sodium hypochlorite for 30 seconds, then the cells were inoculated onto the spinach leaves. For exposure on the spinach leaves, EC was first inoculated onto leaves; then the inoculated spinach leaves were dipped into 100 ppm sodium hypochlorite. After inoculation, the spinach was packaged to obtain high-oxygen (20%O2/3%CO2) and low-oxygen (0%O2/15%CO2) atmospheres, respectively. The packages were stored at 4°C or 15°C, and EC populations were quantified at six sampling points during 14 days of storage. The data were analyzed by DMFit and Microfit to demonstrate the growth curve and kinetics. In general, there were no apparent differences in EC behavior between the chlorine treated and control groups for most of the conditions. However, in certain conditions, the chlorine-treated cells showed a faster decrease and/or slower increase in population than the control packages. Generally, low temperature and high oxygen conditions led to lower survival than high temperature and low oxygen. For EC exposed in solution, the EC population showed a greater reduction and faster decrease in the high-oxygen than low-oxygen packages at 4°C. At 15°C, the lowoxygen condition resulted in a faster growth rate (+0.43 log CFU/ml/day) than high oxygen packages (+0.17 log CFU/ml/day). Also, in the 4°C high-oxygen condition, the chlorine-treated cells showed a greater population decrease (-0.95 log CFU/ml) than the control groups (-0.57 log CFU/ml). For EC exposed on the spinach, the low-oxygen packages showed greater population levels and faster growth rates compared to the highoxygen packages at 15°C. At 4°C, chlorine treated groups and control groups showed no apparent differences for both low- and high- oxygen packages. At 15°C, the chlorine treated packages showed less increase in population (+0.79 log CFU/ml) than the controls (+1.58 log CFU/ml) in low-oxygen; and the control groups increased at a faster growth rate (+0.57 log CFU/ml/day) than the chlorine treated ones (+0.25 log CFU/ml/day).
M.S. in Food Safety and Technology, December 2011
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