Potato Glycoalkaloid
Potato Glycoalkaloid Toxicity: Solanine
by Andrew Montario. Cornell University.
Each year the world produces approximately 350 million tons of potatoes. The U.S. per capita consumption of potatoes is about 61 kgs per year. As you can see potatoes (Solanum tubersum) serve as a major food source as well as an inexpensive source of energy and good quality protein. Potatoes are grown mainly for human consumption but they are also widely used as food for livestock.
It is a less commonly known fact that potatoes produce compounds called glycoalkaloids that have been shown to be toxic to both man and to animals. At high enough levels the glycoalkaloid found in potatoes known as solanine can cause irritation of the gastrointestinal tract, impairment of the nervous system, and it is believed that they can cause teratogenic or birth defects. Neurological signs can include ataxia, convulsions, coma, muscle weakness, and involuntary urination.
Potatoes produce several different glycoalkaloids. The most well known one of these is Solanine; it is believed to be responsible for food poisoning. Solanine is a glycoalkaloid containing a steroid alkaloid nucleus with a side chain of three sugars. Solanine is the most active cholinesterase inhibitor found in food due to its location in edible portions of plants.
It has the ability to prevent the breakdown of acetylcholine -a very active neurotransmitter- in the human body. The accumulation of acteylcholine in neuromuscular junctions impairs the function of the nervous system and its effect on organs. Studies have linked birth defects such as spinal bifida in humans as well as breeding problems in animals to potato glycoalkaloids.
Alpha-Chaconine is another glycoalkaloid that is found in potatoes.
- As you can see both solanine and chaconine have the same aglycone as solanine, solaridine.
- The side chain sugar on the other hand is different in solanine and in chaconine.
- Both chaconine and solanine have been tested on mice, rabbits, and chick embryos and they have been shown to have similar toxicities.
Solanine Levels and Burning Sensation
Steroidal glycoalkaloids (SGA’s) of potatoes may be detrimental to the health of humans and animals, but they are beneficial to the plants. The SGA’s such as solanine are thought to be a component of the certain varieties resistance to insects. The insects they provide protection from the potato beetle, potato leafhopper, and wireworms.
It is also believed that SGA’s may assist some crops in resistance to disease. At a low pH level some SGA’s have shown to have antifungal effects. Synergistic fungi inhibitory effects were reported when alpha-chaconine and alpha-solanine where present simultaneously.
In addition low levels of glycoalkaloids are required in order to produce a desired flavor. More bitter varieties contain excess solanine and other SGA’s and are more toxic as well.
Solanine levels above 14mg/100g are bitter in taste. Cultivar with greater than 20mg/100g cause a burning sensation in the throat and mouth. The second most abundant steroidal glycoalkaloid in potatoes is alpha-chaconine.
In ruminant animals, potato glycoalkaloids are hydrolyzed to solanidine. Solanidine is then further metabolized into 5,6 dihydro analog.
The Mechanism of Action
Solanum alkaloids are cholinesterase inhibitors which result in neural function impairment. A cholinesterase inhibitor is a chemical compound that inhibits acetylcholinesterase from removing acetylcholine from neuromuscular junctions. Acetylcholine is the neurotransmitter of the parasympathetic nervous system.
It is released from the terminal bouton of the preganglionic nerve fibers when action potential frequencies reach a sufficient level. When an inhibitor of acetylcholinesterase such as solanine is present in the cleft acetylcholine accumulates. The presence of acetylcholine in nerve tissue or organs is responsible for the neurological signs associated with solanine poisoning.
Other Glycoalkaloids in Potato Tissues
Other glycoalkaloids that are known to accumulate in tissues of the body and tend to concentrate most significantly in the liver. High concentrations have also been found in other major organs such as the kidney, heart, lungs, and in the brain.
Toxic Concentrations in Potatoes
In the human alpha-solanine and alpha-chaconine(another glycoalkaloid in potatoes) toxicity begins with gastrointestinal disturbances, vomiting, diarrhea, abdominal pain, then followed by neurological disorders at higher doses, low blood pressure, fever, rapid weak pulse. The symptoms listed are associated with sublethal doses
Little information is available on the chronic toxicity of glycoalkaloids. There are indications that alpha-solanine and other potato glycoalkaloids can accumulate in tissues.
Solanine “poisoning” has a variety of symptoms. These symptoms may include: nausea, diarrhea, abdominal cramps, fever, headache, weak pulse, rapid breathing, hallucinations, delirium, and induce a coma.
Reasons for Low Oral Toxicity
Despite the effects this chemical has, it’s oral lethal dose is relatively high in animals; it has a low oral toxicity. This low oral toxicity is a result of how the compound of how the compound is dealt with by the body.
First, solanine levels in the blood are low after ingestion due to poor absorption by the gastrointestinal tract. Second, it is removed from the body fairly rapidly in both the urine and the feces, usually within 12 hours, preventing accumulation in the tissues. Third, intestinal bacteria aids in the detoxification by hydrolyzing the glycoside into solanidine(aglycone), which is less toxic than solanine and also poorly absorbed.