The antibotulinal effect of sodium propionate was evaluated by a factorial-design experiment and by an inoculated-pack study on a shelf-stable beef product. Processing of samples involved curing, cooking, vacuum packing, and gamma irradiation. The factorial-design experiment involved 240 samples treated with 0, 0.8, 2.0, and 3.3% sodium propionate, challenged with 101 to 105 spores of type A Clostridium botulinum per package, irradiated with 2.5, 5, 7.5, and 10 kGy, and stored at 28°C for up to 4 months. In the pack study, 110 samples with 2% added sodium propionate were challenged with 108 spores of C. botulinum per package, irradiated with 12.5 kGy, and stored (28°C) for 8 months. Addition of 0.8% sodium propionate resulted in a delay (compared to control samples) in toxigenesis of 18 (5 kGy), 34 (2.5 kGy), and 34 (7.5 kGy) days, while no toxin was detected in samples irradiated with 10 kGy. Samples containing 2 and 3.3% sodium propionate were not toxic at any irradiation dose assayed. A safety level, expressed as the number of decimal reductions (DR = log 1/P) for the combination 0.8% sodium propionate and 10 kGy, was estimated to be >4.4. In the inoculated pack study, 2 of 107 samples became toxic, and the safety level treatment resulted in 10.7 DR. Sodium propionate in combination with other processing factors was very effective in preventing C. botulinum toxigenesis: it can be used as a further safety hurdle in the development of shelf-stable meat products.

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