The potato (Solanum tuberosum) is a widely consumed staple food, but it belongs to the nightshade family (Solanaceae), which is known for containing toxic compounds. While the potato tuber is generally safe, parts of the plant and certain conditions of the tuber contain naturally occurring toxins. Therefore, the potato plant carries a potential for toxicity depending on the part consumed and how it was grown or stored.
The Protective Toxin
The potato plant’s toxicity comes from natural chemicals called glycoalkaloids, primarily alpha-solanine and alpha-chaconine. These two compounds account for over 95% of the total glycoalkaloid content in cultivated potatoes. The plant synthesizes these compounds as a defense mechanism against environmental threats.
These compounds function as natural pesticides, protecting the plant from insects, fungi, and other pathogens. Their concentration increases when the plant is stressed or damaged. High levels of glycoalkaloids give the potato a bitter taste and can cause a burning sensation in the mouth.
Which Parts of the Potato Plant Are Dangerous
The highest concentrations of glycoalkaloids are found outside the edible tuber. This includes the leaves, stems, flowers, and the small, inedible fruit, which resembles a miniature green tomato. These aerial parts of the plant should never be consumed due to their high toxin levels.
The toxicity related to the tuber itself is concentrated in specific areas that have been exposed to light or are actively growing. New sprouts, often called “eyes,” contain elevated levels of glycoalkaloids as they are metabolically active parts of the plant. Additionally, any area of the potato skin or flesh that has turned green is a strong indicator of increased toxin presence.
The green coloring is harmless chlorophyll, but its production is triggered by light exposure. Light exposure simultaneously stimulates the biosynthesis of glycoalkaloids. A normal, non-illuminated potato tuber contains an average of 12–20 milligrams of glycoalkaloids per kilogram. In contrast, a green tuber can contain 250–280 milligrams per kilogram, with the highest levels (1,500–2,200 mg/kg) found in the green skin.
Recognizing Symptoms and Safe Handling
Ingesting potatoes with high glycoalkaloid levels can lead to solanine poisoning, with symptoms appearing 10 minutes to 12 hours after consumption. Mild reactions involve gastrointestinal distress, such as nausea, vomiting, abdominal pain, and diarrhea. These symptoms often resolve on their own without specific treatment.
In more severe cases, which are rare, the poisoning can affect the central nervous system, leading to headaches, fever, confusion, and in extreme circumstances, hallucinations or paralysis. If severe symptoms occur, it is important to seek immediate medical attention. The toxic dose for humans is estimated to be between 2 to 5 milligrams of glycoalkaloids per kilogram of body weight.
To minimize the risk of poisoning, proper storage is recommended in a cool, dark place, since light exposure increases toxin production. When preparing potatoes, always remove any sprouts or eyes, and cut away all green areas and deep bruises before cooking. If a potato is extensively green throughout or has a noticeably bitter taste, it should be discarded entirely. Cooking methods like boiling or frying only minimally reduce the glycoalkaloid content.