Viability of listeria. monocytogenes in raw ground beef

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he effect of some stress factors on the viability of isolated L. monocytogenes serotype 1 inoculated in raw ground beef was studied.The temperature of 70°c for more than 20 minutes in the center of the product will ensure a total kill of L. monocytogenes, even in a heavily contaminated one. Freezing and storage of the inoculated raw ground beef at – 18°c decreased the counts from 8.041 to 2.00 log CFU/g after 8 wecls. L. monocytogenes significantly decreased from 7.033 to 6 log CFU/g by the week 3 and from 4.5 to 2.566 log CFU/g by the week 7.Nisin at concerntration of 1600 IU/g of raw ground beef stored at 4°c may be useful in controlling of L. monocytogenes.The treatment of the inoculated ground beef with potassium sorbate at 0.26 % exhibited significant inhibitory properties against L. monocytogenes from 7.952 to 3.996 log CFU/g by the day 21 of refrigerated storage.The treatment of the inoculated ground beef with potassium nitrite (125 ppm) significantly decreased L. monocytogenes counts from 7.65 to 3.139 by the day 21.Combination of nisin, potassium nitrite and potassium ascorbate produced enhanced listeriidal effect more than the use of each preservative alone

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