LPT 321: Meat Science (1+1)

THE PUBLIC HEALTH ASPECT OF CANNED FOODS

• Improvements in canning industry during recent years, together with greater appreciation of its hygienic requirements, have done much to remove the prejudice in the minds of lay public against canned foods based on the opposition that canned foods might cause Food poisoning.
• Food poisoning is usually the result of improper handling of food during preparation or storage, and, with the exception of botulism, food poisoning outbreaks are always caused by bacteria which would be destroyed during processing.
• Botulism is caused by the botulinal toxin produced by Clostridium botulinum (or Cl. botulinum) an obligate anaerobe which is ubiquitous, being found in the air, soil, waters, intestinal tracts of fish and mammals, and gills and viscera of crabs and other shellfish.
• Clostridium botulinum grows well in low-acid foods such as canned vegetables, processed meats, sausages, smoked fish, and other seafood products.
• There are seven known types of Clostridium botulinum bacteria. These differ in such characteristics as proteolytic activity, tolerance to salt and reduced water activity, minimum growth temperature and resistance to destruction by heat.
• The nonproteolytic type B, E and F strains can grow at refrigerated temperatures, but produce spores of very low heat resistance. These types cause problems primarily in pasteurized or unheated foods. Because they are nonproteolytic, no off-odor or evidence of spoilage may be produced with toxin development
• Type C strains cause botulism in birds, turtles, cattle, sheep and horses.
• Type D is associated with forage poisoning of cattle and sheep in Australia and South Africa.
• No outbreaks of type G have been reported; however, type G has been isolated in cases of sudden and unexpected death in humans.
• Inactive Clostridium botulinum spores are found in soil and water throughout the world. It is comparatively harmless in the spore form.
• A lower processing temperature is however permissible in the case of a few special packs such as cured meats, in which the curing salts have an inhibitory effect on the growth of organisms and the production of its toxins.
• In Britain, there is no record that canned foods have been incriminated in outbreaks of botulism.
• Staphylococci and more rarely streptococci are now recognized as a cause of food poisoning and the majority of foods in which pathogenic staphylococci have been concerned were prepared or unheated foods such as cheese, salad, milk or ice cream.
• These organisms are ubiquitous in nature being found in air, water, milk and sausage but the main source is the human or animal body where they are normally present on the skin, in the intestines and in the respiratory tract.
• Staphylococci, however, are relatively susceptible to heat and even the more resistant staphylococcal enterotoxin, which may withstand a temperature of 100°C for 30 minutes, would be destroyed during commercial processing.
• Cans may occasionally become infected if these organisms gain entrance through a leaking can and in absence of accompanying gas-forming bacteria, the can will not blow. While its contents, though, they appear normal may contain large amount of the organisms and its toxins.
• Most cases of food poisoning now associated with canned foods are the result of contamination of food stuffs after the can is opened, but a number of cases of typhoid fever associated with canned foods have occurred in Britain in recent years.
• The outbreak in Aberdeen in 1964 in which there were over 400 confirmed cases attributed to the entry during the whole processing period of contaminated cooling water into a 6 lbs of tin of corned beef of South American origin.
• Viewing the question as a whole, it may be stated definitely that canned foods are considerably less likely to be a source of food poisoning than are ordinary fresh foods.
• The possibility of canned foods being rendered dangerous by secondary contaminated with pathogenic bacteria also raises the question of the wisdom or otherwise of leaving food in a can after it has been opened.
• So, from the public health point, there is no reason, why an open can properly stored, should not be used as a food container, the only requirement being that it should be kept covered to prevent contamination and that can and its content should be kept cool. But it is the sporulated Cl. botulinum that is able to resist high temperatures and survive a wide range of unfavorable living conditions, such as extreme cold, 5–10 hours in boiling water, and the presence of chemicals. Cl. botulinum reverts to its vegetative form once conditions become favorable and reproduces just like other bacteria. Fortunately, botulinal toxin is not heat resistant like the spore form. It can be inactivated by boiling temperatures of 212 ° F (100 ° C) for at least 10 minutes. The salmonella groups of organism are destroyed with certainity by the temperature attained in commercial processing. The minimum standard of processing now universally recognized by reputable canners ensures the destruction of CI.botulinum spores in low acid and medium acid foods.