Attack of The Green Potatoes
Apr 23rd, 2012 | By MaryEllen | Category: Food, Gardening | Print This Article
Have you ever noticed a slight green tinge to your potatoes? Or maybe you’ve seen the occasional greenish chip in a bag of potato chips. Potatoes sometimes turn green and, no it is not an old wives’ tale that this can poison you. The green part of a potato is toxic for people to eat. The reason, however, may surprise you. What is myth rather than fact is that the green part of a potato tuber is full of arsenic. This misconception has spread perhaps because there is some arsenic in potato plants. The green part of a tuber, however, is poisonous for a different reason.
Even though the green potato will not poison you with arsenic, there are very good reasons to consider the levels of arsenic in your food. The amounts of this toxic element in foods and the types of foods in which it can be found may surprise you.
If you grow potatoes in your garden already, you know about mounding or hilling. When the tubers of potatoes begin to form, you need to keep them covered with soil. As they grow, you need to keep an eye out and make sure they are fully covered. The trick is to cover the tubers without covering too much of the greenery. As you cover the tubers, you end up creating a hill or a mound around the plant, hence the term for this process. The reason for keeping the tubers well covered is the dreaded green potato.
When a potato tuber is exposed to the sunlight, it begins to produce chlorophyll. Chlorophyll is the molecule in green plants that is responsible for collecting energy from sunlight. It is also the molecule that makes plants green. Through the process of photosynthesis, green plants take energy from the sun, carbon from the air and soil, and water to create its own food. Chlorophyll is a crucial step in this process, and the more chlorophyll a plant has, the more energy it can take in and the more food it can create to grow successfully.
So, the greening of a tuber is the potato’s strategy for success. As long as it is exposed to the sun, it may as well be collecting energy from the sun, as the leaves do, and contributing to the process of photosynthesis. Unfortunately, for us, those green spots on the potato are toxic. It is not the chlorophyll itself, however, that is toxic, but another compound that also grows in the green spots.
Toxins in Potatoes
Potatoes, which are members of the nightshade group of plants, produce compounds called glycoalkaloids. They are poisonous compounds and are the source of the name nightshade. When eaten, glycoalkaloids taste bitter and produce a burning sensation on the side of the tongue and in the back of the mouth. Tomatoes and eggplants also contain these compounds as fellow members of the nightshade family.
The specific alkaloid that is produced in potato leaves, stalks, roots, and tubers is called solanine. Solanine is very toxic and is produced in higher quantities in the green portion of a tuber that is exposed to light. They also elevate production of solanine when the tubers are damaged by splitting, cutting, bruising, and rotting. Potatoes produce solanine in all parts of the plant as a protective measure. Solanine acts as a fungicide and a pesticide, protecting the potato plant from invaders and predators.
An entire green potato contains enough solanine to cause serious health problems for anyone who eats it. Solanine consumption causes both gastrointestinal and neurological symptoms. In severe cases of solanine poisoning, the sufferer can become paralyzed or die. Someone who has eaten too much of this toxin may experience the following symptoms:
- Burning sensation in the throat and mouth
- Stomach cramping
- Dilated pupils
- Hypothermia, or low body temperatures
- Slowed breathing and slow pulse
- Vision problems
- Loss of sensation
Most potatoes, if they are not green at all, will not have enough solanine content to cause any symptoms. It is possible, however, that a potato that looks safe to eat can have more solanine than usual. If this is the case, it will taste bitter and you should throw it out. The sprouts that emerge from a tuber are particularly high in solanine, so these should be cut out and thrown away before eating the rest of the potato. Death from solanine is quite rare, but if you see any of these symptoms in someone who has eaten a potato, you should seek emergency medical attention or call poison control.
Although solanine is the toxic compound that concentrates in the green part of a potato, arsenic may still be present in any potato in very low amounts simply by taking up minerals from the earth. These amounts are negligible. What is of greater concern is the arsenic that may be present because of pesticides used and arsenic in irrigation water. A study conduct in Spain found that potatoes that were irrigated with water containing arsenic had up to thirty-five times more arsenic in them than other potatoes. Arsenic levels in water can be a serious concern in some places, and it can cause this toxic element to build up in vegetables.
Arsenic is an element, and in its elemental state, it is a whitish-gray semi metal. It exists naturally in the earth in mineral compounds with sulfur, oxygen, and other elements. Arsenic is toxic to most living things, but there are a few bacteria species that actually depend upon it. Many of the arsenic compounds that we use for semiconductors, pesticides, and other products are poisonous.
Symptoms of arsenic poisoning include headaches, confusion, drowsiness, convulsions, and severe diarrhea. With acute arsenic poisoning, the sufferer will experience vomiting, muscle cramping, hair loss, stomach pain, organ failure, coma, and finally death if enough is consumed. Chronic exposure to low levels of arsenic can include heart disease, stroke, cancer, diabetes, respiratory illness, and vitamin A deficiency, which can lead to night blindness.
The type of arsenic found naturally in the ground and that is taken up in plants and vegetables is organic arsenic. In this form, it is not very toxic and nothing to be concerned about. Inorganic arsenic compounds, on the other hand, are very toxic. Natural, organic arsenic compounds can turn into inorganic compounds in ground water. Exposure to this type of arsenic usually occurs through contaminated drinking water. For adults, 70 to 200 milligrams of this arsenic in a day is enough to be lethal.
Sources of Arsenic
Contaminated drinking water is the most common source of arsenic poisoning throughout the world. This typically leads to chronic, low levels of poisoning, rather than an acute and lethal dose. The World Health Organization recommends that drinking water should have no more than one hundredth of a milligram of arsenic per liter. The Environmental Protection Agency sets that limit for the United States at 10 parts per billion. Poisoning through drinking water is not often an issue in the US, although it is in other places in the world.
Other sources of arsenic that should concern you as a consumer include foods and beverages. Some animal feeds contain arsenic, specifically those for turkeys and chickens. This means that much of the commercial turkey and chicken meat in stores has more arsenic than other foods. Apple juice also can contain elevated amounts of arsenic due to processing with contaminated water. This is particularly a concern with juice imported from China where arsenic from pesticides is a serious problem.
More recently, rice has come under fire for containing a surprising amount of arsenic. A study conducted at Dartmouth found that products containing organic brown rice syrup had significantly higher amounts of arsenic than foods without this ingredient. It has long been known that, because of how it grows, rice takes in more arsenic than other foods.
The EPA and FDA would have you believe that arsenic in foods is not a problem. However, there are no studies that indicate how harmful this low level exposure to arsenic over time could be. Your best bet is to avoid supermarket foods and grow your own. You shouldn’t worry about getting arsenic from your potatoes, though. Just be sure to get rid of the green ones.
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