A comparison of growth of some common meat bacteria on the lean and adipose tissue of beef, pork and lamb

Abstract

Lean and fat samples of normal beef, pork and lamb were inoculated with aerobically and anaerobically grown cells of Hafnia alvei, Serratia liquefaciens, Leuconostoc mesenteroides, Lactobacillus plantarum, Lactobacillus curvatus (beef only) and Pseudomonas putida. Samples were packaged and stored in polyvinyl chloride (PVC) film for 6 days at 5°C and vacuum packaged in high-oxygen barrier (HOB) film for 21 days at 5°C. In addition, dark, firm, dry (DFD) beef samples were inoculated, packaged and stored as described above. Considerable increases in count (range 2.32 to 5.68 log10) of inoculated bacteria occurred on fat samples of beef, pork and lamb during refrigerated storage. Increases in count of H. alvei and S. liquefaciens on fat samples of beef and pork were consistently greater (P < 0.05) than those on comparable lean samples. This was also true, but to a lesser extent, for samples inoculated with L. plantarum. Increases in L. mesenteroides count on fat samples of beef, pork and lamb were either smaller than or did not differ (P > 0.05) from those on comparable lean samples. Growth patterns of H. alvei, S. liquefaciens and L. plantarum on fat versus lean samples of lamb were not consistent. In most cases, growth on samples inoculated with aerobically and anaerobically grown test cultures did not differ. Most changes in pH of [greater than or equal to] 0.5 during storage of samples were decreases in pH of fat samples. Lactic acid bacteria caused sour, rotten, rancid and spicy-mustardy odors. H. alvei caused fishy odors on fat samples. H. alvei or S. liquefaciens grew more extensively on the fat than on the lean samples of normal beef and differences in count between fat and lean of inoculated DFD samples had narrowed considerably or disappeared. Growth of L. mesenteroides was more extensive on the lean than on the fat samples of both normal and DFD beef; it was more pronounced on DFD than on the normal beef. Increases in count of L. plantarum on lean samples of DFD beef packaged and stored in PVC film were greater than those on comparable fat samples. On normal beef, however, increases in count were greater on the fat than on comparable lean samples.