Glycoalkaloids are natural poisons or toxins of plants that act as a defense mechanism of plants against diseases and pests. Glycoalkaloids are mainly obtained from potatoes, but they are also found in raw green or greening tomatoes. Glycoalkaloids in potatoes are called solanine and in tomatoes tomatine. In large doses, they cause a bitter aftertaste and are mildly toxic and harmful to health. They can cause stomach or intestinal pain, diarrhea, vomiting and nervous system symptoms.

Greened potatoes or raw tomatoes are not recommended for consumption. Early potatoes contain more glycoalkaloids than winter potatoes. The concentrations are highest in small tubers and greened potatoes in particular. The above-ground parts of potatoes, including the tubers, and potato sprouts also contain solanine, so they should not be used for food. Germination also increases the glycoalkaloid content of the cells near the sprouts.

The highest glycoalkaloid content is in the potato skin layer. Peeling the potato reduces the glycoalkaloid content by about 60%.

The concentration of natural toxins in potatoes and other vegetables is affected by factors such as soil, variety, growing conditions and factors related to potato storage. Greening of potatoes and thus an increase in glycoalkaloid content can be avoided by, for example, ensuring sufficient mulching during cultivation and protecting the potatoes from light during storage. The light permeability of the consumer packaging also plays a role in the formation of glycoalkaloids. To prevent greening, potatoes should be stored in retail stores, commercial kitchens and households protected from light.