Effects of meat pH on growth of 11 species of psychrotolerant clostridia on vacuum packaged beef and blown pack spoilage of the product.

ABSTRACT

The aim of the study was to determine the effects of meat pH on the abilities of 11 psychrotolerant Clostridium spp. to grow on, and to possibly cause blown pack spoilage of vacuum packaged beef. Beef steaks of pH 5.4-5.6, 5.7-5.9 or ≥6.0, i.e. of normal, intermediate or high pH were prepared and vacuum packaged. Groups of 3 steaks of the same pH range were inoculated with log phase cultures of Clostridium algoriphilum, Clostridium algidixylanolyticum, Clostridium bowmanii, Clostridium estertheticum, Clostridium frigoris, Clostridium frigidicarnis, Clostridium gasigenes, Clostridium lacusfryxellense, Clostridium psychrophilum, Clostridium tagluense or Clostridium vincentii. Each pack was resealed immediately after the steak was inoculated, and pack volumes were determined by water displacement, immediately after resealing and at intervals during storage at 2 °C for 56 days. All of the clostridia grew in packs of high pH beef but none caused pack swelling. Packs of intermediate pH beef inoculated with C. estertheticum began to swell after 14 days, with a mean rate of increase of pack volumes of 6.80 ml/day. One pack of intermediate pH beef inoculated with C. frigoris was swollen after 37 days. Packs of normal pH beef that had been inoculated with C. estertheticum began swelling after 14 days with a mean rate of increase of pack volumes of 7.70 ml/day. Packs of normal or intermediate pH beef inoculated with other clostridia did not swell. After storage, the numbers of most Clostridium spp., as determined by real-time PCR were greater on beef of high pH than of lower pH values, but the numbers of C. frigidicarnis and C. lacusfryxellense were highest on intermediate pH meat, the numbers of C. estertheticum were higher on meat of lower than of high pH, and the numbers of C. tagluense were the same on meat of all pH values. With high pH meat, glucose was reduced to very low level in rinse fluids from packs that had been inoculated with any Clostridium sp. With intermediate and normal pH meat, glucose was reduced to very low concentrations in only rinse fluids from beef that had been inoculated with C. estertheticum.