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, Escherichia coli O157:H7 and strains of Salmonella were compared in ground beef packed in modified atmospheres of 60% CO2/40% N2/0.4% CO (high CO2/low CO mixture), 70% O2/30% CO2 (high O2 mixture) and in chub packs (stuffed in plastic casings). The ground beef was inoculated with rifampicin-resistant 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 and background flora development, was prolonged for the high CO2/low CO mixture compared to the two other packaging methods, but at 10 degrees C the shelf life was < 8 days for all the packaging methods. Growth of Y. enterocolitica 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 high O2 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 about 5 x 10(3) bacteria/g to about 10(4) at day 5 in the high CO2/low CO mixture, while the numbers in the high O2 mixture and the chub packs were about 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 O2 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 high CO2/low CO mixture than in the high O2 mixture. This study shows that the growth of Y. enterocolitica and L. mononcytogenes in ground beef stored in the high CO2 /low CO mixture was not increased as a result of prolonging the 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 of temperature control during storage.
Nissen
H
H
MATFORSK, Norwegian Food Research Institute, Oslovn. hilde.nissen@matforsk.no
Alvseike
O
O
Bredholt
S
S
Holck
A
A
Nesbakken
T
T
D000818:Animals; D002245:Carbon Dioxide / Q000032:analysis; D002417:Cattle; D019453:Escherichia coli O157 / Q000254:growth & development*; D018857:Food Packaging; D008089:Listeria monocytogenes / Q000254:growth & development*; D008460:Meat / Q000382:microbiology*; D012475:Salmonella / Q000254:growth & development*; D013696:Temperature; D015008:Yersinia enterocolitica / Q000254:growth & development*
D002245:Carbon Dioxide