OUTGROWTH OF CLOSTRIDIUM-PERFRINGENS SPORES IN COOK-IN-BAG BEEF PRODUCTS

Clostridium perfringens growth from a spore inoculum was investigated in vacuum-packaged, cook-in-bag ground beef that included 0.3% (w/w) s odium pyrophosphate, pH 5.5 or 7.0, and salt (sodium chloride) at 0 or 3% (w/w). The packages were processed to an internal temperature of 7 1.1C, ice chilled and stored at various temperatures. The total C. per fringens population was determined by plating diluted samples on trypt ose-sulfite-cycloserine agar followed by anaerobic incubation for 48 h at 37C. At 28C, a combination of 3% salt and pH 5.5 was effective in delaying growth for 24 h. At 15C, growth occurred within 6 days in sam ples with pH 7.0, but was delayed until day 8 in the presence of 3% sa lt at pH 7.0. Vegetative cells were not observed even after 21 days of storage at 15C in the presence 3 % salt at pH 5.5. C. perfringens gro wth was not observed at 4C regardless of pH or salt levels. The D-valu es ranged from 23.33 min (3% salt, pH 7.0) to 13.99 min (3% salt, pH 5 .5). Cyclic and static temperature abuse of refrigerated products for 12-15 h did not permit C. perfringens growth. However, temperature abu se of cook-in-bag beef products for periods longer than 15 h in the ab sence of salt led to growth of C. perfringens from a spore inoculum.