29F-27 |
Starved Listeria monocytogenes cells showed increased resistance to killing by nisin and diacetyl |
M. L. SOSTRIN, Center for Food Safety & Quality, Department of Food Science, University of Arkanasas, 2650 N. Young Ave, Fayetteville, AR 72704, R. Nannapaneni, Center for Food Safety & Quality, Department of Food Science, University of Arkansas, 2650 North Young Avenue, Fayetteville, AR 72704, and M. G. Johnson, Dept. of Food Science, Univ. of Arkansas, Center for Food Safety & Quality, 2650 N. Young Ave., Fayetteville, AR 72704-5690. Human listeriosis is associated with the consumption of unpasteurized cheese, dairy products, post processing contaminated of ready to eat meats and raw vegetables. The use of the bacteriocin, nisin is generally recognized as safe and may provide a means of control for L. monocytogenes. Diacetyl, also a lactic acid bacterium byproduct, may also have inhibitory properties for the control L. monocytogenes. Therefore, we hypothesize that a combination of nisin and diacetyl at various concentrations may offer improved control of L. monocytogenes. The effectiveness of nisin on starved cells has not been tested extensively. The objective was to determine the effectiveness of nisin and diacetyl to inhibit the growth of L. monocytogenes under normal cell cultivation and starvation conditions. The inhibitory effects of nisin at (320 or 1,000 IU/ml) or diacetyl (0.25%,0.5%, 1.0% vol/vol) and combinations on L. monocytogenes in PBS were determined using standard plating methods on BHI and PALCAM at 0 and 2 hours post-treatment. Starvation of L. monocytogenes for 7, 14, and 21 days was performed using PBS, pH 7.0. At day 0 or 7 of starvation, 2 hour exposure to nisin (1,000 IU/ml) and diacetyl (1%) gave 8 to 9 Log CFU/ml reductions on BHI. At day 14 or 21 the reductions were only 4 Log CFU/ml (or 99.99% more survivors). Using PALCAM to recover cells, the same trends in log reductions were observed, indicating the cells were indeed killed not injured by the nisin and diacetyl treatments. The nisin and diacetyl combinations gave more knockdown of L. monocytogenes then either separately. L. monocytogenes cells starved for 14 or more days are much more resistant to the combinations than controls.
Session 29F, Food Microbiology: Control of foodborne microorganisms by antimicrobials
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