Effects of Temperature and pH on the Growth of Bacteria Isolated from Blown Packs of Vacuum-Packaged Beef

Abstract

Bacteria recovered from the microflora of blown packs of vacuum-packaged beef were identified as Leuconostoc mesenteroides, Lactococcus lactis, Carnobacterium maltaromaticum, and Clostridium estertheticum, with L. mesenteroides predominant. Isolates of these lactic acid bacteria all grew in peptone yeast extract glucose starch broth (PYGSB) at temperatures between −2 and 30°C but generally grew more slowly and over a more restricted temperature range in meat juice medium (MJM). A C. estertheticum isolate and the type strain of C. estertheticum subsp. estertheticum (ATCC 51377) both grew in PYGSB and MJM at similar rates at temperatures between −2 and 17°C and grew at 20°C in MJM but not in PYGSB. Square root models of the variation of the growth rate with temperature indicated that the C. maltaromaticum isolate and the C. estertheticum strains grew at similar rates that were faster than those of the other isolates at temperatures between 22 and 0°C. The L. mesenteroides and L. lactis isolates grew in PYGSB at pH 5.0, but the C. maltaromaticum isolate and both strains of C. estertheticum did not grow in PYGSB at pH ≤ 5.3. C. estertheticum stopped growing in MJM buffered at pH 6.5 when glucose was exhausted, although these bacteria then utilized lactate. The findings suggest that, like carnobacteria, C. estertheticum may predominate during the early stages of development of the spoilage microflora of vacuum-packaged beef but that C. estertheticum will likely be inhibited by a falling pH and so may be only a minor part of the spoilage microflora when maximum numbers are attained.