The fate of Clostridium perfringens spores exposed to ozone and/or mild heat pretreatment on beef surfaces followed by modified atmosphere packaging Original Research Article

Clostridium perfringens is a natural contaminant of raw beef products that can proliferate to dangerous cell levels under conditions of temperature abuse. Spores of the bacterium were inoculated onto irradiated London broil beef at levels of 3 log10 spores/g beef. Samples of beef (7.5×10.0×1.0 cm) were treated with aqueous ozone (5 ppm O3 for 5 min), or heat (60°C for 30 min), or both and then vacuum-packaged to 2 kPa for up to 10 d storage at 37°C, 25°C, or 4°C. Storage at 37°C resulted in increases in viable counts after 1 d to over 7 log10 cfu/g beef, whereas storage at 4°C prevented spore germination and growth for all treatments. At 25°C, heat-treated beef samples reached 6 log10 cfu/g viable counts in 2 d and spores/vegetative cells on control or ozone-treated samples did not germinate or grow through the first day of vacuum-packaged storage. Modified atmospheres with increasing CO2 concentration were also compared with regard to bacterial survival during beef storage at 25°C. C. perfringens spores remained dormant in control and ozone-treated beef during a 10-d storage at 25°C. Pretreatment with heat increased germination and outgrowth during storage of beef, whereas ozone treatment and no treatment controls were effective in inhibiting spore germination and outgrowth in combination with increasing CO2 concentrations above 30% or refrigeration. These data support the avoidance of heat in the pretreatment of raw beef.