Poisonous potato lacks appeal
What can you do to avoid falling foul of the 'killer potato'? Dr Karl digs a little deeper to uncover the potentially lethal characteristics of the common spud.
Last time, I talked about how the humble potato could kill you, and how it belonged to a botanical family with many sinister members, such as tobacco, mandrake and deadly nightshade. In the case of the potato, it makes a poisonous chemical called solanine.
But how can a potato make solanine, after it's been dug out of the ground?
Well, even after it's been separated from its plant and taken out of the soil, the potato is still a living entity, with its own metabolism.
It makes chemicals, and this is very much controlled by the quality of the light that lands on it, whether it's sunlight in the garden shed sneaking under a door or under a roof, or flooding in through a window, or artificial lights.
All artificial lights are different — fluorescent lights, tungsten lights, the special lights in the supermarket that are designed to make food more attractive, and so on.
To the untrained eye, all these lights, especially if you've been under them for a while, simply appear white. But each of these lights has its own colour balance — a reddish tinge, or greenish, or bluish, or yellow if it's a sodium light.
If it's a reddish light that lands on the potato, it will make chlorophyll, giving the potato a green colour.
If the potato is hit by bluish or ultraviolet light, it will make solanine, by a completely separate chemical pathway. But the potato itself will not change colour.
If the light contains both red and blue, the two processes can happen at the same time.
So, there are four possibilities for a potato. It can have turned green and rich in solanine, or it can be green and low in solanine.
Or it can be non-green and rich in solanine, or it can be non-green and low in solanine. It's all so confusing.
So what is the average person, without access to a full biochemistry lab supposed to do?
First, if it's green, you can just cut off about five millimetres of the potato flesh from the outer layer. Or, you can just dump the whole potato into the compost.
And second, if it's not green, go by the taste test. If it tastes bitter, don't eat it.
And just in case you want to 'know the enemy' and familiarise yourself with the taste of solanine, first grab a potato with little shoots growing out of it.
Then, to taste solanine safely, just nip your teeth gently on the green tip of a shoot, taste it on your tongue, and spit it out.
Farmers have long known that green or sprouted potatoes can kill stock. Actually, livestock are relatively resistant to solanine, while we humans are very sensitive to it.
Over the years, solanine in potatoes has killed at least 30 people, and made over 2000 very sick.
For example, a 1933 outbreak in Cyprus poisoned about 60 people, of whom one died.
In north Korea in 1952–53, 382 people were affected by solanine, of whom 22 died.
In an English school in 1978, 78 students were poisoned, and three of them were close to death, but survived. In this case, uneaten potatoes were recovered two days later from residues intended for pig swill, and found to contain astronomically high levels of solanine: 250 micrograms of solanine per gram of peeled potato.
At this stage, we don't exactly know the fatal dose of solanine for humans, but it's probably around three to six milligrams of solanine per kilogram of body weight.
And even though there's not a lot of hard data, it seems that some people are more susceptible to solanine than other people.
In lab tests, eating potatoes with this level of solanine gave a two-part sensation: an immediate bitter taste lasting about one minute; followed by a strong burning taste which lasted about five minutes.
The taste is along the sides of the tongue, and the back of the mouth. However, regular ingredients used in cooking (such as salt, oils and flavours) can easily mask this bitter taste.
Almost certainly, the real figures for potato solanine poisoning are much greater than those officially recorded. But most cases would be lumped in with gastroenteritis or general food poisoning and so go unnoticed as the work of the killer potato.
So what should you do to protect yourself, bearing in mind that half a kilogram of fully green potato can make a 45-kilogram person quite sick?
Cut away any green sections. If the potato is bitter, don't eat it. Avoid fried potato skins (a popular appetizer in some restaurants) if they have any green tinge.
But don't get too paranoid. The philosopher and explorer, Alexander von Humboldt, said that South America gave us a great curse, tobacco, and a great blessing, the potato.
Published 28 April 2010
© 2020 Karl S. Kruszelnicki Pty Ltd