When we think about the variety of natural food substances and the methods by which each of these is handled during processing, we realize that all kinds of microorganisms are possible contaminants. The type of food substance and the processing or preservation method used for it may favor contamination by certain groups of microorganisms. Most food substances provide the means by which various microorganisms can grow and multiply. Given this chance, these microorganisms can cause alterations in the food’s qualities, such as in its flavor, odor, and appearance.
Foods that are improperly sealed and canned at home favor the growth of botulin, the bacterium that causes botulism (food poisoning characterized by acute gastrointestinal and nervous disorders). On the other hand, commercially canned foods are virtually risk-free. This, of course, is on condition that the canned foods are in good condition.
In spoiled canned foods, the microorganisms involved are classified according to the acidity of the contents. Of the many microorganisms that can cause spoilage in canned foods, bacillus and clostridium stand out, mainly because of their ability to resist heat.
There are several types of spoilage of commercially canned foods, and these four are considered the most important: flat sour spoilage, thermophilic anaerobe spoilage, sulfide spoilage, and putrefactive anaerobe spoilage. Certain conditions of the can or its contents may be signs of spoilage, and these are what you have to watch out for.
In the flat sour spoilage type, which is caused by the bacterium Bacillus stearothermophilus, the can appears to have lost vacuum, possibly on storage. The appearance of its contents usually has not changed, but they have slightly abnormal odor and are sour.
In the thermophilic anaerobe spoilage type, which is caused by the bacterium Clostridium thermosaccharolyticum, the can swells and appears to burst any moment. Its contents appear fermented and sour and have butyric odor.
In the sulfide spoilage type, which is caused by the bacterium Clostridium nigrificans, the can appears flat, possibly from the product’s absorption of hydrogen sulfide gas. Its contents are usually blackened, and the odor is much like that of a rotten egg.
In the putrefactive anaerobe spoilage type, which is caused by the bacterium Clostridium sporogenes, the can swells and appears to burst any moment. Its contents may appear partially digested and have a typical putrid odor.
Simply put, a can that does not appear to be in good condition (example, swells out or has dents around the rim or seam) should be thrown out; food contents that appear bubbly, spongy, or moldy or smell odd should likewise be cast aside. Accidentally eating spoiled canned foods can cause headache, blurred vision, muscle weakness, and even paralysis. When this happens, do not delay in getting medical help.