How to prevent botulism

Press, 23 April 1984, Page 12

How to prevent botulism

Kathy Taylor is a top pentathlon competitor. The British sportswoman’s skills in shooting, riding, swimming, fencing, and long distance run-

ning have featured in many television programmes. Now Ms Taylor, who has a degree in physiology, is working as a television commentator.

The admission to Rotorua Hospital earlier this year of two women suffering from botulism created a great deal of interest in this rare and often fatal food poisoning. These were the first confirmed cases in New Zealand.

Botulism is caused by a bacteria found in soil and marine silt that forms spores, resistant to heat and drying, which become dust borne and can contaminate a variety of foods. Given the right conditions, the spores germinate and produce a toxin that causes botulism.

The Department of Health’s director of public health, Dr C. M. (Maxwell) Collins, says a series of conditions has to exist before the toxin is produced. “While the sequence of events in the Rotorua cases has yet to be confirmed, it’s believed the toxin developed in bottled mussels and watercress.”

Dr Collins says that while some New Zealand recipe books contain methods for preserving shellfish with puha or watercress, these

recipes are not strictly traditional. “In the days before bottling became commonplace, the method of preservation was to cook the shellfish and then string them on strips of flax to dry in the sun.”

Dr Collins says the foods commonly involved in botulism cases overseas include vegetables, fish and shellfish, along with meat and poultry that haven’t been heated sufficiently during canning or bottling. “Poor home processing is responsible for most cases.” It is generally accepted that bottled fruits are safe because fruit is less likely to be contaminated by the bacteria spores and because its acidity inhibits their germination.

“Although there have been overseas reports of home preserved pears and apricots being responsible for botulism, these examples are very rare and the risk is extremely small. “Thorough washing of the fruit and bottling by standard methods should be safe. Over-ripe fruit, especially

tomatoes, shouldn’t be used because of reduced acidity." says Dr Collins. The Department's public health division has prepared the following guidelines for the prevention of botulism in the home. Pressure Cooking The botulism spores can only be destroyed by heating to 115 C (i.e. more than boiling point) and held at that temperature for about 25 minutes. Therefore, low-acid foods such as vegetables, meat and seafood must be canned or bottled under pressure in a pressure cooker. They should never be preserved by using a hot oven, boiling water bath or open bottle method.

Before serving, these foods should be transferred to an open saucepan and brought to a rolling boil for 20 minutes to destroy the toxin. Remember not to taste before heating. Bottling shellfish and green vegetables carries

the risk of botulism. It is best to eat such relishes on the day they are made. Because of the hazards involved in the home bot- • tling of low-acid foods, it is recommended that meat, fish and vegetables be preserved by freezing instead. Freezing Freezing doesn’t destroy botulism spores, but pre- . vents them from germinating and producing toxins. Only fresh food should be frozen and in amounts that can be used at one meal. The food should be used as soon as it is thawed. This is a much simpler and safer method for the home preservation of lowacid foods. Other methods Botulism spores do not germinate and produce toxins in solutions of sugar, salt or vinegar strong enough to preserve the food. Therefore, home made vegetable pickles and relishes are quite safe if the amount of vinegar etc. recommended in con-

ventional recipes is used.

This method of home preservation is not recom- - mended for meat and : seafoods, including shellfish. Detection Unlike some other food; spoilage bacteria such as ' yeast and moulds, the botulism toxin does not affect the taste, smell or appearance of preserved food. The growth of botulism bacteria is inhibited” by the presence of organisms that do affect these characteristics of food.