| The USDA requires that relative growth of Clostridium perfringens should not exceed 1 log unit in all cooked beef products. To assist the meat industry comply with this regulation, FSIS recommends that all cooked meat be continuously cooled from 54.4°C to 26.7°C within 1.5 hr, and from 26.7°C to 4.4°C within 5 hr. Different organic salts (sodium acetate, sodium diacetate, sodium lactate, and sodium citrate buffered at pH 4.4, 5.0, and 5.6) and spices (chili, garlic and herbs, curry, oregano, and clove powders) alone or combined were assessed as secondary barriers for the control of C. perfringens growth in cooked vacuum-packaged beef products cooled during FSIS alternative cooling procedures. Emphasis was placed on sodium citrate for which the minimal inhibitory concentration against C. perfringens growth during an 18 hr cooling procedure was evaluated, as well as its possible mode of action using transmission electron microscopy (TEM).; Results showed that 0.25% (w/w) sodium acetate did not comply with USDA requirement during an 18 hr cooling period. Sodium diacetate at 0.25%, sodium lactate at 2%, and all sodium citrate buffered solutions at 0.5% resulted either in growth less than 1 log unit (sodium diacetate), or in C. perfringens population reduction (sodium lactate and sodium citrate) during an 18 hr cooling. None of the spices at 1% met USDA requirement except for oregano during a 15 hr cooling. The longer the cooling time, the more spices with potent antibacterial effect lost their activity. Significant growth inhibition in samples containing oregano or clove during 15 hr cooling was no longer significant during 21 hr cooling. Sodium lactate combined with any of the five spices showed some synergy during the 21 hr cooling period. TEM analysis of the mode of action of sodium citrate, heat and cooling treatments on the morphology of C. perfringens revealed that the organic salt induced cell wall, membrane, and overall intracellular structure loss of integrity. Heat seemed to affect cells primarily by resulting in cytoplasmic material coagulation and breakdown of the cell wall and membrane, probably as a consequence of denaturation of protein membrane. |
