Potatoes are a staple in many diets, yet green patches on their skin are a common sight that can raise questions. This discoloration is not merely cosmetic; it signals underlying chemical alterations within the potato. Understanding this green hue is important for ensuring potato safety.
Understanding the Green Color
The green color on potatoes is due to chlorophyll, the pigment that gives plants their green appearance. Chlorophyll itself is harmless and poses no risk to human health. However, chlorophyll production often occurs alongside the formation of solanine, a natural glycoalkaloid. Solanine is a bitter-tasting compound that serves as a natural defense mechanism for the potato plant against pests and diseases.
Small amounts of solanine are not harmful, but higher concentrations can lead to adverse effects. The amount of solanine in potatoes is low, but it can increase significantly when potatoes are exposed to light or physical damage. Symptoms of solanine toxicity can include gastrointestinal issues such as nausea, vomiting, and abdominal pain. In more severe cases, neurological symptoms can occur. Potatoes with solanine concentrations exceeding 0.1 mg/g can taste bitter, and levels above 0.2 mg/g may cause a burning sensation in the mouth.
Why Potatoes Turn Green
Potatoes turn green due to light exposure, whether natural sunlight during growth or artificial light during storage. When potato tubers are exposed to light, they produce chlorophyll as part of a natural process similar to photosynthesis.
Beyond light, other environmental factors influence greening and solanine development. Physical damage, such as bruising or cuts, can stimulate solanine production as a defense response. Higher storage temperatures can also increase greening. The potato variety and its maturity also affect how readily it greens and produces solanine; white-skinned varieties, for example, may green more easily than red or russet types.
Safe Practices for Green Potatoes
To prevent potatoes from turning green and accumulating solanine, proper storage is important. Potatoes should be kept in a cool, dark, and dry place, such as a pantry, cellar, or cupboard, away from direct light. Avoiding plastic bags and opting for paper bags or breathable containers can improve air circulation and help prevent moisture buildup, which contributes to spoilage. Store potatoes away from heat-emitting appliances.
When encountering green potatoes, assess the extent of the discoloration. If only small, superficial green spots are present, these can be safely peeled or cut away along with any sprouts or “eyes,” as solanine is concentrated in and just beneath the skin. However, if a potato is extensively green or has a noticeably bitter taste, it indicates high solanine levels throughout and should be discarded entirely. Cooking can reduce solanine levels, but peeling is the most effective method for removal, as much of the compound is in the outer layers.