Comparison between the growth of Yersinia enterocolitica, Listeria monocytogenes, Escherichia coli O157 : H7 and Salmonella spp. in ground beef packed by three commercially used packaging techniques

Growth of the pathogens Yersinia enterocolitica, Listeria monocytogenes, Es cherichia coli O157:H7 and strains of Salmonella were compared in ground be ef packed in modified atmospheres of 60% CO2/40% N-2/0.4% CO (high CO2/low CO mixture), 70% O-2/30% CO2 (high O-2 mixture) and in chub packs (stuffed in plastic casings). The ground beef was inoculated with rifampicin-resista nt or nalidixic acid/streptomycin-resistant strains of the pathogens (final concentration 10(2)-10(3) bacteria/g) and stored at 4 and 10 degrees C for up to 14 days. At 4 degrees C the shelf life, based on colour stability an d background flora development, was prolonged for the high CO2/low CO mixtu re compared to the two other packaging methods, but at 10 degrees C the she lf life was <8 days for all the packaging methods. Growth of Y. enterocolit ica was nearly totally inhibited both at 4 and 10 degrees C in the high CO2 /low CO mixture, while the bacterial numbers in the samples packed in the h igh O-2 mixture increased from about 5 x 10(2) bacteria/g at day 0 to about 10(4) at day 5 at 4 degrees C and to 10(5) at 10 degrees C. Growth in the chub packs was even higher. L. monocytogenes showed very little growth at 4 degrees C in all treatments. At 10 degrees C there was slow growth from ab out 5 x 10(3) bacteria/g to about 10(4) at day 5 in the high CO2/low CO mix ture, while the numbers in the high O-2 mixture and the chub packs were abo ut 10 times higher. Growth of E, coli O157:H7 at 10 degrees C in the ground beef was nearly totally inhibited in both the high CO2/low CO mixture and the high 0, mixture. Growth in the chub packs was higher, as the number of bacteria increased 3 log in 5 days. The Salmonella strains (S. typhimurium, S. dublin, S. enteritidis and S. enterica 61:k:1,5,(7)) in the ground beef stored at 10 degrees C for 5 and 7 days grew to a higher number in the hig h CO2/low CO mixture than in the high O-2 mixture. This study shows that th e growth of Y. enterocolitica and L. mononcytogenes in ground beef stored i n the high CO2/low CO mixture was not increased as a result of prolonging t he shelf life. However, the observed growth of strains of Salmonella at 10 degrees C in this mixture and in chub packs does emphasise the importance o f temperature control during storage. (C) 2000 Elsevier Science B.V. All ri ghts reserved.