Food Safety, Preparation and Storage Tips
Cooperative Extension, College of Agriculture & Life Sciences, the University of Arizona
Clostridium botulinum is a bacterium which grows in the absence of oxygen and produces a potent neurotoxin. It can be found throughout the environment in mud, dirt and dust as heat-resistant spores. These spores can survive in foods that are incorrectly or inadequately heat processed. When these foods are stored at room temperature in the absence of oxygen, such as home canned foods, the spores can become actively growing cells producing botulinum toxin.
Botulism results from eating food containing the neurotoxin and only very minute amounts of the toxin can make you sick. The onset of symptoms is usually 18 to 36 hours, and sometimes as long as 8 days, following ingestion of the food containing toxin. Early signs can include of marked tiredness, weakness, dizziness, usually followed by double vision and increasing difficulty in speaking and swallowing. Difficulty in breathing, weakness of other muscles, abdominal distention, and constipation may also be common symptoms. Paralysis can progress downward, usually starting with the eyes and face. When the diaphragm and chest muscles are involved, breathing is inhibited and death can result. Rapid diagnosis and treatment is important, especially in infants.
Most of the 10 to 30 outbreaks that are reported annually in the U.S. are associated with inadequately processed, home-canned foods, but occasionally in commercial processed foods as well as sausages, meat products, canned vegetables, and seafood products (such as canned and smoked fish) have been involved most frequently botulism. Restaurant foods such as sauteed onions, chopped bottled garlic in oil, potato salad made from baked potatoes, and baked potatoes themselves have been responsible for recent outbreaks.
Almost any food that is not acidic (pH above 4.6) can support growth and toxin production by C. botulinum. Therefore, canned foods stored without refrigeration or microbial inhibitors need to receive a sufficient heat treatment to destroy any botulinum spores that might be present. NEVER deviate from the approved processing method when preparing home canned foods. The botulinal toxin can be inactivated by a heat treatment of 176° F (80° C) for at least ten minutes. The presence of toxin is not necessarily indicated by a product defect such as an off odor or taste. When in doubt, throw it out!
Material written by Ralph Meer and Scottie Misner, April 1998.