Potatoes (Solanum tuberosum) are a global food staple, yet they belong to the nightshade family, a group of plants known for containing natural toxins. This relationship often generates confusion regarding the safety of the potato plant, particularly its non-tuber parts. While the potato tuber itself is consumed safely, other sections of the plant contain compounds that are not safe for human consumption. Understanding which parts of the potato plant are toxic is important for home gardeners and consumers.
Clarifying the Potato Plant and Its “Seeds”
The term “potato seeds” can refer to two very different things, and clarifying this distinction is important. What a gardener calls a “seed potato” is not a true botanical seed but is actually a small piece of the tuber used for vegetative propagation. These seed potatoes are essentially clones of the parent plant. They contain the same potential for toxicity as any tuber, especially if they are heavily sprouted or green.
The plant’s true seeds are found inside its fruit, which are small, round, green berries that look like tiny, immature tomatoes. These berries are rarely encountered by consumers as they are typically only produced after the plant flowers and are often removed by commercial growers. The true potato berries possess high concentrations of the toxic compounds found in the aerial plant parts. These true seeds are mainly used by plant breeders to develop new varieties.
Solanine: The Compound Responsible for Toxicity
The source of the potato plant’s toxicity lies in a group of compounds called glycoalkaloids, primarily Solanine and Chaconine. These compounds act as the plant’s natural defense mechanism against pests, insects, and fungal diseases. Solanine and Chaconine are present in all parts of the plant, but their concentration levels vary significantly.
The toxic effects of these glycoalkaloids result from their ability to disrupt cell membranes and interfere with the nervous system. Symptoms of poisoning can include gastrointestinal distress like nausea, vomiting, abdominal pain, and diarrhea. More severe cases can involve neurological symptoms such as headache, apathy, drowsiness, or paralysis.
Toxicity risk is generally considered to begin when the total glycoalkaloid level exceeds 200 milligrams per kilogram of fresh potato weight. A safe level is considered to be below 100 milligrams per kilogram. A toxic dose for a human is estimated to start in the range of 2 to 5 milligrams of glycoalkaloid per kilogram of body weight. Normal, properly stored potatoes contain levels far below this, typically averaging 12 to 20 milligrams per kilogram.
Identifying and Avoiding Poisonous Potato Plant Parts
Consumers are most likely to encounter elevated glycoalkaloid levels in tubers that have been improperly stored. Exposure to light, whether natural sunlight or artificial, triggers the potato to produce chlorophyll, causing the skin to turn green. This exposure also stimulates a significant increase in glycoalkaloid production. This green hue is a visual indicator of potential toxicity, though the toxin itself is colorless.
Potato sprouts, commonly referred to as “eyes,” also contain a high concentration of these toxins. The glycoalkaloids are most heavily concentrated in the outer layer of the potato, particularly in the skin and the area immediately beneath it. For example, a green tuber can contain 250 to 280 milligrams of glycoalkaloid per kilogram. The green skin itself may contain up to 1,500 to 2,200 milligrams per kilogram.
To prevent toxicity, potatoes should always be stored in a cool, dark, and dry place, which slows the production of both chlorophyll and glycoalkaloids. Any green sections of the potato, along with the sprouts, should be generously cut away before cooking. Cooking methods like boiling or baking do not reliably destroy Solanine, as the compound is relatively heat-stable. Degradation requires temperatures above 338°F (170°C). Peeling the potato can remove 30 to 80% of the Solanine, making physical removal the most effective safety measure.