What are glycoalkaloids?
Potatoes are part of the Solanum genus, the nightshade family, and naturally contain a group of toxic compounds called glycoalkaloids. The two most prevalent and concerning glycoalkaloids in potatoes are solanine and chaconine. These compounds are part of the plant's natural defense system, protecting it from insects, bacteria, and fungi. In properly grown and stored potatoes, the levels of these toxins are low and considered safe for human consumption. However, when a potato is stressed or improperly stored, its glycoalkaloid content can rise significantly.
Where are glycoalkaloids concentrated in potatoes?
The concentration of these toxins is not uniform throughout the potato. The highest levels are found in the plant's non-edible parts, like the leaves, stems, and sprouts. Within the edible tuber, the concentration is highest just beneath the skin, especially in areas that have turned green. The "eyes" or sprouts are also highly concentrated with solanine and should be removed. A bruised or damaged potato can also have an increased glycoalkaloid content near the affected area. The green color is actually harmless chlorophyll, which develops with light exposure, but it serves as a visual indicator that the plant is also producing solanine. A more reliable indicator of dangerously high toxin levels is a bitter taste or a burning sensation in the mouth.
Symptoms of solanine poisoning
Symptoms of solanine poisoning primarily affect the gastrointestinal and nervous systems. The onset can range from as little as 10 minutes to up to 12 hours after ingesting high-solanine foods. The severity of symptoms depends on the amount of toxin consumed. Mild cases often present as simple digestive upset and may be mistaken for a common stomach bug.
Common symptoms
- Nausea and vomiting
- Diarrhea
- Abdominal pain and cramping
- Headache and dizziness
- Burning sensation in the throat
Severe symptoms
At very high doses, solanine can cause more serious neurological issues. These are rare but can include:
- Hallucinations
- Paralysis or loss of sensation
- Fever
- Dilated pupils
- Slow pulse and breathing
- In extreme cases, death has been reported, though it is very rare.
How to prevent solanine exposure
Fortunately, avoiding solanine poisoning is straightforward with proper storage and preparation. The key is to prevent the potato from producing high levels of the toxin in the first place and to remove any parts that have.
Prevention guidelines
- Store potatoes in a cool, dark, and dry place to prevent them from turning green and sprouting.
- Avoid buying potatoes that already look green or have sprouts.
- Always cut off all sprouts and any green-colored parts before cooking.
- Peel the skin. Since most of the glycoalkaloids are concentrated near the surface, peeling is a very effective way to reduce the toxin content.
- Discard any potatoes with significant greening or a bitter taste. The taste is a strong signal that the glycoalkaloid levels are elevated.
The effect of cooking on solanine
Cooking methods are surprisingly ineffective at destroying glycoalkaloids. High temperatures are required to break down solanine, and common cooking methods don't get hot enough for a long enough time. Boiling, baking, and microwaving have been shown to reduce solanine levels only minimally. Deep-frying at very high temperatures ($>170^{\circ}C$) for an extended period can be more effective, but it is not a foolproof solution. Peeling and trimming remain the most important steps.
Low-Toxin vs. High-Toxin Potatoes: A Comparison
To summarize the key differences, consider this table:
| Feature | Low Glycoalkaloid Potato (Safe) | High Glycoalkaloid Potato (Unsafe) |
|---|---|---|
| Appearance | Uniform, pale skin color. No sprouts. | Obvious green coloration, especially under the skin. Visible sprouts. Bruised areas. |
| Taste | Neutral, earthy potato flavor. | Distinctly bitter taste, and potentially a burning sensation in the mouth. |
| Storage | Kept in a cool, dark, and dry environment. | Stored in direct light, at warmer temperatures, or for an extended period. |
| Toxin Level | Negligibly low, within safe limits. | Elevated and potentially hazardous levels. |
Conclusion
The toxic substance in potatoes is a group of compounds called glycoalkaloids, primarily solanine. While normally present in safe, low levels, this natural pesticide can accumulate to dangerous concentrations if the potato is exposed to light or stored improperly, leading to noticeable greening and sprouting. The key to prevention lies in proper storage and preparation, such as keeping potatoes in a cool, dark place and always peeling away any green or sprouting parts. By following these simple guidelines, you can continue to enjoy potatoes safely without risk. For more information on potato plant poisoning, refer to the MedlinePlus article from the National Institutes of Health.
