Solanine is a naturally occurring compound found in certain plants. It belongs to a class of chemicals known as glycoalkaloids, which are produced by members of the nightshade family. This substance serves a protective role for the plant, functioning as a built-in defense mechanism that wards off insects, fungi, and other predators.
Foods Containing Solanine
The most well-known source of solanine is the potato. While commercially grown potatoes are screened to have low solanine levels, concentrations can increase significantly when tubers are exposed to light. This exposure causes the potato to turn green, which is due to harmless chlorophyll, but it indicates that conditions were suitable for producing more solanine. Damaged or sprouting potatoes also contain higher levels of this compound.
Other common vegetables from the nightshade family contain solanine, though often in different parts of the plant. In tomatoes, for instance, the highest concentration is found in the leaves and stems, with much lower amounts in the unripe, green fruit and negligible amounts in ripe fruit. Eggplants and peppers also produce solanine, primarily in their foliage rather than the parts typically consumed.
Solanine Toxicity and Symptoms
While solanine is toxic, the amount present in most commercially available produce is too low to cause harm. Poisoning is rare and results from consuming large quantities of improperly stored, green, or spoiled potatoes. The body’s reaction to solanine can involve both gastrointestinal and neurological symptoms, and initial signs include nausea, vomiting, stomach cramps, and diarrhea.
A burning sensation in the throat, headache, and dizziness can also occur. In more significant cases of exposure, neurological effects may appear, such as confusion, fever, or a loss of sensation. Doses of 2 to 5 milligrams of solanine per kilogram of body weight can lead to toxic symptoms. However, the levels in properly handled commercial potatoes are less than 0.2 mg/g, making it difficult to reach a harmful dose through normal consumption.
The mechanism of toxicity involves the disruption of cell membranes. When ingested, solanine can interfere with mitochondrial membranes, which are responsible for cellular energy production. Symptoms can appear anywhere from 30 minutes to 12 hours after ingesting a food high in the compound.
Minimizing Solanine Exposure
When choosing potatoes, select firm ones and actively avoid any that show signs of greening, sprouting, or physical damage. The green color itself is chlorophyll, but it serves as a visual cue that higher levels of solanine may be present. Checking for firmness and an even skin color helps ensure the potato has been stored correctly.
Potatoes should be kept in a cool, dark, and dry place. Light exposure stimulates the production of both chlorophyll and solanine, so keeping them out of direct sunlight or well-lit areas prevents greening and subsequent solanine formation. A pantry or cupboard is an ideal environment.
During preparation, physically removing the parts with the highest solanine concentration is the most effective method of reduction. A significant amount of the compound is found in or just beneath the skin, so peeling potatoes can lower the solanine content by 30-80%. It is also important to cut away any sprouted sections or areas with a green tinge before cooking. While deep-frying at high temperatures (170°C) can help lower solanine levels, boiling is less effective.