Green Potatoes: Are They Dangerous?

Question
“My question is about eating potatoes that have gone green.

I have cautioned at least 3 times over the past 18 months my local supermarkets who mark down the bags of green potatoes to sell. I am fearful the very people who would go for such a bargain are the poor & uneducated who do not realise the harm these could do to an unborn baby.

I checked out my concerns via the CSIRO site & they seem to back up what I say. But even so everyone else thinks I’m crazy. I won’t buy green potatoes myself; my concern is for other who unwittingly does so not knowing they can be harmful.

Am I right to go on complaining at the point of sale?”

Christine
Adelaide, South Australia

Reply

That’s a good question.

Potato tubers may be green and non-toxic. Potatoes may also look normal and be lethal.
Unless you carry a laboratory in your pocket, remember this taste test:
Toxic potatoes taste bitter, and this is the best way an amateur can tell the difference.

I wouldn’t complain because you first need proof they are toxic and that requires laboratory testing.

Solanine is the toxin concerned. Potatoes can contain a lethal amount of solanine without going green. And green potatoes can contain zero solanine. Why? Potatoes greened up under sunlight become toxic, but potatoes that have greened up under shop fluorescent lights can remain non-toxic.

Tungsten filament lamps (phased out in Australia in 2009) emit red light, which stimulates tubers to turn green, but it does not stimulate solanine production.

Ultraviolet light stimulates solanine production, but tubers do not green up. Fluorescent lights do not emit much ultraviolet light, so shop potatoes do not produce much solanine.

Fluorescent ‘grow lights’ are designed to cultivate plants in glasshouses or indoors by replicating natural sunlight. Both horticultural lights and sunlight include light from both the red and blue ends of the spectrum. Sunlight and ‘grow lights’ turn potatoes green and stimulate the manufacture of solanine. LED lights can include light wavelengths from either end, or both, of the spectrum.

Why then do we not hear more reports about people dying? I can’t find a reference to green potatoes on the NSW Poisons Information Centre website (Westmead Children’s Hospital). There have been so few solanine-related deaths worldwide that the actual lethal dose for a human isn’t known. Animal testing doesn’t help. Even though farm animals are occasionally killed, humans are more sensitive to this toxin, and infants and people living with HIV may be more susceptible. It’s likely that most cases of mild potato poisoning are lumped in with salmonella-related ‘food poisoning’ – a quick vomit and no need to consult a GP.

Potato, Solanum tuberosum, is a member of the Solanaceae family. Relatives include eggplant, capsicum, chilli, tomato, Angel’s trumpet (Brugmansia), tobacco, blackberry nightshade (Solanum nigrum) and deadly nightshade.

Boiling potatoes does not neutralise solanine, nor does microwaving. Deep frying and baking do if the potatoes are heated at 170C or above: at this temperature solanine is destroyed.

Solanine-rich potatoes taste bitter, it makes them very hard to eat. But if you peel off the green outer layer the rest inside is perfectly safe to eat, and that is information worth sharing to avoid people of any educational background (or economic status) from wasting good food.

Jerry Coleby-Williams
15th June 2012