Microbial ecology of decontaminated and not decontaminated beef carcasses

The objective of this study was to investigate spoilage microflora of decontaminated and not decontaminated beef carcasses. Carcasses after skinning and after chilling at two beef plants (A, a small plant where no interventions but dry chilling are used; B, a large plant where multiple antimicrobial interventions and spray chilling are used) were swab-sampled for determination of carcass microflora. The numbers of aerobes, Pseudomonas, Brochothrix thermosphacta, lactic acid bacteria (LAB), and Enterobacteriaceae (EB) on carcasses at plant A after skinning were 5.2, 3.7, 2.8, 3.9, and 1.6 log cfu 15,000 cm-2 and they were not significantly different (p>0.05) from those on carcasses at plant B at equivalent times. The numbers of EB were significantly lower (p<0.05) on carcasses after chilling at both plants. However, no difference was observed for the other four groups of microorganisms (p>0.05). At plant A, the microflora on carcasses after skinning and after chilling included 18 and 19 bacterial species, with Psychrobacter (30.9%) and Psychrobacter (42.9%) being the respective predominant genus, respectively. At plant B, the microflora after skinning and after chilling included 21 and 17 bacterial species, with Chryseobacterium (18.6%), Kocuria (18.6%) and Brevibacterium (18.6%), and Pseudomonas (33.3%) being the respective predominant genera. The spoilage microflora of decontaminated beef carcasses is similar in numbers to that of conventionally produced carcasses, suggesting the decontamination treatments for beef carcasses may not cause major difference in storage life of chilled vacuum packaged beef, the major form of beef for international and domestic trading in North America.