Saturday, October 1, 2011


Mice are more suceptible to listeria if exposed to relatively low doses of ionizing radiation. See my last 2 posts. Naval radiation research in the 1960s established this finding. See my last 2 posts.

In our present era, listeria has become a major problem in some produce, particularly green, leafy vegetables. Ionizing radiation is used to kill listeria.

The catch is that the dose must be high. When the level of ionizing radiation is not high enough, the listeria growth actually increases after a period of storage time.

Ionizing Radiation Sensitivity of Listeria Monocytogenes and L. Innocua Inoculated on Endive (Cichorium Endiva) Authors, Niemira, B., X Fan, K. Sokorai, & C. Sommers (2003, January 6, 2003). Journal of Food Protection.
"Leafy green salad vegetables, such as endive, can be contaminated with bacteria that cause serious illness in humans. Ionizing radiation can inactivate these pathogenic bacteria, making the food product safer to eat. To determine how well this process works with endive, leaf pieces and leaf homogenates of endive were inoculated with one of two bacteria, either the pathogenic bacterium Listeria monocytogenes or Listeria innocua, a non-pathogenic surrogate bacterium. The radiation sensitivity of the two strains were found to be similar, although L. innocua was more sensitive to the type of suspending leaf preparation. During refrigerated storage following irradiation, the population of L. monocytogenes on inoculated endive was briefly suppressed by a very low radiation dose calibrated to achieve a 99 percent reduction. However, the pathogen regrew after 5 days until it exceeded the bacterial levels on the untreated control after 19 days in storage. Treatment with a higher radiation dose, equivalent to 99.99 percent reduction, suppressed L. monocytogenes throughout the course of refrigerated storage. Doses up to the 99.99 percent kill level had no significant effect on the color or texture of endive leaves..."

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