Whether you bring vegetables home from the store or harvest them from your garden, proper storage is a key factor in retaining their freshness and quality. Vegetables begin to decompose and become active breeding grounds for harmful microorganisms that can cause foodborne illnesses, sometimes even before the recommended use-by dates. Even when you keep vegetables refrigerated, mold, bacteria and yeasts eventually can make them unsafe to consume.
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All vegetables can become toxic when you keep them past their safe storage time or at temperatures that are not cold enough to kill harmful microorganisms. The safe storage time for vegetables varies. Soft, watery vegetables -- such as spinach, lettuce, squash and greens -- remain in prime condition for less than one week, according to the University of Nebraska-Lincoln Cooperative Extension. Cut vegetables -- such as convenience containers of chopped green peppers, diced onions and coleslaw mix -- deteriorate rapidly after two to three days. Dense, hard vegetables, such as carrots and beets, last up two weeks.
Bacteria, mold and yeast are the primary sources of illnesses caused by consuming old vegetables. Damaged or bruised vegetables are prime targets for decay and infection during storage, but even vegetables that are in good condition might harbor dangers. Imperfections on the surface of your vegetables are prime locations for the entry of invisible bacteria. Some bacteria are present on the skin of vegetables when you bring them into your home, and they have the ability to thrive even in a cold environment. Mold and yeasts often result from less-than-ideal temperatures during storage or simply keeping vegetables so long that they begin to decay, which provides an opportunity for these culprits to develop and grow.
The University of Nebraska-Lincoln Cooperative Extension recommends that you store vegetables that require refrigeration between 34 and 40 degrees Fahrenheit, preferably in the crisper section of the refrigerator. Vegetables such as onions, potatoes and tomatoes, which do not require refrigeration, continue to ripen after harvest. To store them safely, keep them in a cool, dark place in an area that has adequate ventilation.
Eating vegetables infected with mold, yeast or bacteria can result in serious illness or even death. Some symptoms of food poisoning from old vegetables include vomiting and diarrhea, sometimes accompanied by a fever. Mold on vegetables also causes respiratory problems when you inhale the spores. Discard soft, watery vegetables that have an unusual smell, black spots or a fuzzy growth. These are all signs of decomposition, which increases the likelihood of microbial infection. Some harder vegetables -- such as cabbage, broccoli, onions and potatoes -- are safe to eat after you remove the infected sections, according to the Baylor College of Medicine. However, when you cut away the infected area, it is possible to miss the roots of molds and yeasts inside your vegetables. Take care to keep your knife from touching the spoiled area. This leads to cross-contamination of the unspoiled part.