Dynamic changes of selected microbiological and physical parameters in fresh jointed beef

During the performance of microbiological analyses, important groups of microorganisms whose action may have a significant influence on the quality of chilled beef meat stored aerobically and vacuum-packed were monitored in samples of beef on days 1, 3, 7 and 14. Samples of beef rump (musculus semimembranosus) and sirloin (musculus longissimus thoracis et lumborum) from young animals (n = 9) were used. The initial concentration of 104 CFU.cm-2 increased under aerobic conditions during the seven days of storage to a total of 107 CFU.cm-2. Higher total counts of microorganisms were detected in rump than in sirloin at the beginning of storage. A lower count of microorganisms was found in vacuum-packed meat after 14 days of storage than in unpacked meat on day 7. A similar trend was found for the numbers of psychrotrophic microorganisms. Even on day 14 of storage, coliform bacteria counts in vacuum-packed beef were as much as two orders of magnitude lower than in beef stored aerobically. No visible growth of mould was seen in the samples of meat stored. The number of yeast was relatively low at the beginning of storage (of the order of 102 CFU.cm-2), though their number then increased gradually up to 104 CFU.cm-2 in unpacked meat. Lower counts (103 CFU.cm-2) were found in vacuum-packed meat. The colour difference ΔE*ab on day seven of storage of the meat was higher in rump meat (5.2) than in sirloin (4.7). Discoloration of the meat (ΔE*ab = 5.19) and an increase in pH (6.10) were clearly evident when surface slime, which was evident at microorganism counts of the order of 108 CFU.cm-2, appeared.