Microbiological Testing in Canned Foods

Consumers have changed their lifestyle and begun to buy processed canned foods on a regular basis. They are adequately aware about checking expiry, use before and best by dates, ingredients for allergens and nutritional information for health reasons. However, sometimes canned foods can get contaminated with organisms that consumers might not be aware of. Most consumers avoid buying dented or swollen canned foods as they identify these with unsafe food.

Swollen Cans

Swollen cans are generally linked to botulism and microbiological testing can reveal if the food is contaminated with Clostridium botulinium or it is swollen because of overfilling, or closing cans when food is cool. Botulism can cause a number of health hazards including problems in the nervous system, cause muscle and chest weakness and also prove fatal. These organisms can withstand high temperatures and even exist without oxygen. Swelling can also occur when acids in the food product react with the metal of the cans, which causes hydrogen and spoilage. High altitude or rise in temperature also causes cans to swell, therefore, there is a need to test canned foods in a food testing laboratory for spores and rods and also because some microorganisms than can contaminate canned foods and produce no gas.

Leaked Foods

Organisms can also grow in canned foods when there is leakage from the can or when the food is under-processed. Defects, punctures and rough handling of cans can cause leakage which leads to spoilage. Bacterial growth detected in microbiological testing on surfaces of cans. If Clostridium botulinum spores or toxin, or both are found then the hazard is proved. Most botulism spoilage in canned foods is caused by bacteria rods and spores which can lead to spoilage in infant formula, starch, flour, cereals, dehydrated milk, soy proteins and even sugar.


Under-processing of canned foods can also cause contamination either because it has been under cooked because it does not reach adequate temperatures. Sometimes the product is already so contaminated that processing may be insufficient. Changes in formulation or unhygienic handling of the product can also cause contamination. Food testing labs analyse intact cans for specific organisms which indicate that the food is under-processed unless there are other indications. The food testing labs will also determine if the cans are intact and under-processing is not because of drained weight or product formulation.

Sometimes the product in the can is spoiled but there is no microorganism is detected during food testing. In this case it is possible that the spoilage may have occurred before processing or died during storage. Microbiological food testing laboratories also test for contaminants which are often present in the handling equipment which is used throughout the canning process. Contaminants can also be present on the skin of the food handlers, in the soil and on the raw materials themselves. Microbiological testing of raw materials and food testing of finished products even during storage must be carried out to ensure food is safe and has not deteriorated in any way.