Recovered Bacteria Associated with Gas Accumulation in Vacuum-Packaged Fresh Kosher Ground Beef Stored at Refrigeration Temperature

Vacuum packaging and storage at chilled temperatures are commonly used to prolong the shelf life of meat. Under these conditions, cold-tolerant facultatively anaerobic spoilage microorganisms not only can grow but the conditions are more favorable for their growth because these conditions eliminate competition from cold-tolerant aerobic microorganisms. The objective of this study was to identify bacteria that caused gas formation and accumulation in vacuum-packaged refrigerated fresh kosher ground beef as well as from processing plant environment samples. A total of 87 vacuum-packaged ground beef (∼454 g size) and 33 environmental samples were received from a kosher processing plant. The initial populations of aerobic bacteria (AB), psychrotrophic bacteria (PSYB), Enterobacteriaceae (EB) increased by 0.58-1.09 log CFU/g, while the population of lactic acid (LAB) increased 3.18 log CFU/g after 5d at 2-4 °C. After 5 d storage at 2-4 °C, 34% of the packages exhibited gas accumulation. The accumulated gas reacted with lead acetate and formed a brown-black color indicating hydrogen sulfide (H₂S) formation, and the ground beef had a slight off-odor. Lactococcus lactis, Enterobacter cloacae, and Klebsiella oxytoca were the most isolated from environmental samples. Based on the results from the present study, the potential bacteria responsible for gas accumulation and distention of the vacuum-packaged ground beef were Leuconostoc mesenteroides (LAB), Lactobacillus curvatus (LAB), and Serratia liquefaciens (EB). The bacterial strains isolated from 5 d storage distended packages after 5 d storage were dominantly LAB, while the bacterial strains isolated after 56 d storage were mainly EB. These results indicated that LAB are potentially responsible for gas formation that occurs early postpackaging.