Most of us know that undercooked meat and poultry may carry threatening bacteria – both Salmonella and E. Coli bacteria are frequently found in the intestines of poultry, cattle, and other farm animals. But many people don’t realize that raw fruits and vegetables can also carry infected bacteria. This includes mung bean sprouts, a popular ingredient in many Chinese dishes.
In December 2005, over 400 people in Ontario became ill with salmonella poisoning after eating contaminated mung bean sprouts. The sprouts were sold at several outlets throughout Ontario, including Chinese groceries. In 2001, several people throughout Alberta became ill after eating at Asian restaurants. All of the restaurants had received contaminated mung bean sprouts from a single supplier. And in 2002, the US Food and Drug Administration issued a warning against eating raw sprouts (including mung bean sprouts) after an outbreak of food poisoning in several western states.
How Does Food Become Contaminated?It’s easy to see how meat becomes contaminated – animals frequently carry the bacteria in their intestines, which can be passed on if the meat isn’t thoroughly cooked. That’s why E. Coli (Escherichia coli) is commonly called “hamburger disease.” But how are salmonella and E. Coli bacteria transferred to fruits and vegetables?
The journey from farm to grocery store provides several opportunities for contamination. On the farm, fruits and vegetables may come into contact with unclean water during washing or irrigation. Food transported on trucks that are also used to deliver livestock may be exposed to contaminated animal manure.
Food handlers, unaware that they are carrying bacteria (not everyone becomes ill) may unknowingly transfer it from their hands to the food they are handling. This type of person to person transfer is easily preventable through safe food handling procedures - such as hand washing and wearing disposable gloves - but it’s impossible for the consumer to know if these have been rigorously followed. Add the fact that up to 20 people may have handled the food before it reaches your kitchen, and you can see why foodborne illness is a serious concern.
Mung Bean Sprouts – a Special ConcernMung bean sprouts pose a double threat when it comes to bacteria. The optimal growing conditions for mung bean sprouts - a warm, humid environment - provides the perfect conditions for bacteria to pass from the seeds to the sprouts. Worse, mung bean seeds themselves may be contaminated, meaning that growing your own sprouts to use in cooking is no guarantee that they are bacteria-free.
What Can You Do?
There is often no visible outward sign that mung bean sprouts are contaminated. Still, there are a few things you can check for when purchasing mung bean sprouts:
- buy only refrigerated sprouts
- look for sprouts that are crisp, with the buds attached
- avoid sprouts that are brown or have a strange odor
- use tongs to pick up loose bean sprouts
Cooking Sprouts Cooking food at high heat is the best way to destroy bacteria such as salmonella. Unfortunately, mung bean sprouts taste best when lightly stir-fried – overcooked sprouts lose their crisp texture and turn brown and limp. And of course, thoroughly cooking sprouts robs them of nutritional content (mung bean sprouts are high in Vitamin C). The result is that mung bean sprouts may still be contaminated after stir-frying (many of the victims in the 2005 Ontario outbreak became ill after eating stir-fries).
What can you do? It’s a bit of a trade-off between taste and appearance, and health concerns. You can of course, cook the sprouts for a longer time than called for in a recipe. Another option is to briefly blanch the bean sprouts in boiling water before stir-frying. Drain, rinse in cool water, and drain again thoroughly before adding the sprouts to the stir-fry.
More About Mung Bean SproutsSay it With Sprouts - the role of sprouts in Chinese cooking, and lots of Chinese recipes with mung bean sprouts
Chinese recipes with mung bean sprouts - appetizers, main meals, side dishes and vegetarian
Sprouting at home - tips for growing your own mung bean sprouts