Effect of pH on the Germination of Spores of Clostridium estertheticum in Meat Juice Medium

Introduction: Early onset blown pack spoilage (EOBPS) of vacuum packaged chilled raw beef and other meats is characterized by gross swelling of packs at early times during storage. Clostridium estertheticum, a strictly anaerobic spore former, has been identified as the primary cause of EOBPS. The meat must have been contaminated with spores rather than oxygen sensitive vegetative cells of C. estertheticum before packaging. Therefore, to understand how EOBPS might be controlled, it is necessary to establish the conditions required for germination and outgrowth of C. estertheticum spores.

Purpose : The objective of this study was to determine the effect of pH on the germination of spores of C. estertheticumin meat juice medium (MJM).

Methods:  Anaerobic MJM of pH 5.00, 5.50, 6.00, 6.50, 7.00 and 8.00 was inoculated with C. estertheticum spores (1 X 10⁵ CFU/ml). Spore germination was monitored using a modified differential spore stain (Wirtz-Conklin). The spores remaining in the MJM suspensions were counted at 0 h, 4 h, 8 h, 24 h, 31 h, 48 h and 72 h. The effect of pH on outgrowth was monitored over 20 days by observation of gas accumulation in Durham tubes in suspensions of spores in MJM of different pH values.

Results: The numbers of remaining spores decreased quickly within 4 h incubation. The spores remaining after 72 h at pH 5.00 and pH 7.00 were 37% and 19%, respectively, of the initial numbers, showing that the germination of spores of C. estertheticum was enhanced as the pH approached neutrality. As the pH increased, the time before gas production was decreased, with gas production being apparent after 8 and 20 d incubation of MJM of pH 7.3 and 5.7, respectively.

Significance: The normal pH of beef muscle tissue (5.5-5.8) is less favorable for germination and outgrowth of C. estertheticum spores than are higher pH values. Modification of meat surface pH might be a possible approach to prevention of EOBPS in vacuum packaged beef.