A bulletin for the Australian Food Industry June 1995
Contents: Regulation of the production of uncooked, fermented meat products | Cadmium levels in Australian food | Nutrient claims | Biotechnology of food crops | Science and our food | Preservation of vegetables in oil and vinegar
Preservation of vegetables in oil and vinegar
In Italy two separate incidents of food poisoning due to Clostridium botulinum have been associated with the consumption of roasted eggplant in oil.
In 1991 Australian authorities took precautions against this sort of incident by regulating that this class of product must not have a pH greater than 4.6. The pH of a product is a measure of its acidity. Foods with a pH below 4.6 do not in general support the growth of food poisoning bacteria including C.botulinum. The necessary pH adjustment for these products can be achieved only by adding acid to the vegetable material. Vinegar, which is a solution of acetic acid, is the usual choice. Citric acid and lemon juice are other possible acidifying agents.
Attempts to preserve these products without acidification seem to be based on the false assumption that the addition of oil has a preservative effect. This is incorrect. The only function of the oil is to prevent oxidation from the air in the container which can lead to discolouration of some foods. By excluding air from the surface of the vegetable, one is establishing anaerobic conditions which actually favour the growth of some types of bacteria. Unfortunately, C.botulinum is one of these bacteria.
For further information read our factsheet on this subject.
Food Science Australia
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