Low Acid Canned Food Microbiology

While low-acid foods may be contaminated with viruses, yeast, molds, parasites, and bacteria, it is the spore-forming bacteria that are of greatest concern from the standpoint of sterilization. The bacterium most important for low-acid canned foods is Clostridium botulinum, which produces spores that survive boiling. When the vegetative cells of C. botulinum grow, they produce potent neurotoxins (Types A, B, and E are of greatest significance) that can cause death if consumed. C. botulinum Type A and proteolytic strains of Type B have decimal reduction (D) values at 250°F (121°C) of 0.10 to 0.20 minutes (5), the D value being the time in minutes at the specified temperature to destroy 1 log, or 90%, of the population. Thus, thermal processes for low-acid canned foods must be designed to destroy the spores of this organism. By convention, a process equivalent to 12D is considered adequate to protect the public health. However, there are other Clostridia important in food spoilage that produce more heat-resistant spores. To produce shelf-stable products, processes are therefore designed to destroy the spores of organisms such as PA 3679, an organism similar to Clostridium sporo-genes, that has a D25o°f value of 0.50 to 1.50 minutes (5). The heat treatments required to render low-acid foods commercially sterile will destroy viruses, yeast, molds, parasites, and bacterial pathogens such as Salmonella and Escherichia coli 0157:H7.

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