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Glycoalkaloids: green potatoes, sprouts, and why bitter means stop

A potato is a nightshade, and like the rest of its family it defends itself chemically. Solanine and chaconine are glycoalkaloids: bitter, heat-stable, concentrated in the skin and in the green tissue where light has been. This is the one place where “it tastes bitter, spit it out” is genuine food-safety advice.

Not a diagnosis. Serious glycoalkaloid poisoning is rare but real, and it starts with digestive symptoms and can progress to neurological ones. If someone becomes unwell after eating a strongly bitter or badly green potato dish, contact a poisons centre or emergency service. Ordinary potatoes stored and trimmed sensibly are not a health concern, and “avoid all nightshades” is not supported advice for the general population.

What green actually tells you

The green on a potato is chlorophyll, and chlorophyll is harmless — you eat it by the bowlful in every salad. What makes it matter is that the same light exposure that produced the chlorophyll also drives glycoalkaloid synthesis. The colour is a witness, not the culprit.

Because the two respond to the same trigger but are not the same substance, they can come apart. A potato can develop high glycoalkaloid levels from damage, stress or sprouting without turning noticeably green, and that is where the bitter taste becomes the more reliable signal. Bitterness and a burning sensation at the back of the throat are the practical warning, and the sensible response is to stop eating and throw the dish out.

The distribution within the tuber is steep. Concentrations are highest in the sprouts, in the skin and the few millimetres beneath it, and around the eyes and any damaged or green area. The flesh in the middle of a sound potato carries very little. Generous peeling and cutting well past any green or sprouting therefore removes most of the problem, and a potato that is extensively green or heavily sprouted is not worth rescuing.

Cooking does not save you, storage does

Glycoalkaloids are heat-stable. Boiling barely touches them; baking and microwaving do little; deep frying reduces them somewhat, at temperatures well above what home cooking usually reaches. There is no preparation that makes a bitter, green potato safe, which is why every piece of official advice on this compound is about buying, storing and trimming rather than about cooking.

Storage is the lever. Keep potatoes dark — a paper sack or a closed box, not a clear bag on a lit shelf — cool, dry and unbruised, and away from onions, which release moisture that speeds sprouting. Bruising and cutting both trigger glycoalkaloid production at the wound, so a bag of knocked-about potatoes deteriorates faster than a careful one.

There is a genuine tension in the temperature advice, and it is worth knowing about: cold storage below about 4 °C slows sprouting but converts starch to reducing sugars, and reducing sugars are what turn into acrylamide when the potato is later fried or roasted. Cool but not cold — a larder rather than a fridge — is the compromise, and it is why potato packets say not to refrigerate.

Nightshades in general

Tomatoes contain tomatine, aubergines and peppers contain related compounds, and all of them appear on “avoid nightshades” lists aimed at people with arthritis or autoimmune conditions. The levels in ripe, ordinary produce are far below anything of toxicological interest, and green unripe tomatoes are the only entry in that group that carries a meaningfully higher content — which is why fried green tomatoes are eaten in modest quantities and not as a staple.

The claim that nightshades drive inflammatory arthritis has not been supported by trial evidence. What has been shown, repeatedly, is that tomatoes and peppers travel with better outcomes in cohort studies, along with the rest of the vegetable aisle.

The European Food Safety Authority reviewed glycoalkaloids in food and concluded that the compounds warrant attention, particularly for young children whose smaller body weight makes the same dose larger; the opinion is the document to read for the numbers. The long-standing informal industry ceiling for total glycoalkaloids in table potatoes — 200 mg per kilogram — predates it and is what breeders have worked to for decades.

Glycoalkaloidspor grupo de alimentos

Faixas, não decimais. Onde uma quantidade publicada para um alimento concreto não pôde ser verificada contra um documento, esta superfície imprime a faixa em vez de um número — e cada alimento abaixo liga à sua própria página de nutrição para ver o que mais há nele.

O que muda o número

• Light drives synthesis, so a clear bag on a lit shelf is the worst possible storage.
• Damage and bruising trigger production at the wound; handle and store gently.
• Sprouting raises it sharply — cut sprouts out generously, and discard heavily sprouted tubers.
• Cooking does not remove it: boiling, baking and microwaving leave it essentially intact.
• Peeling removes most of it in a sound potato, because the concentration is in the outer few millimetres.

Onde mais estes alimentos são assinalados

Alimentos elevados nesta página que também se sentam numa faixa elevada em pelo menos duas das outras quinze. Faixas tranquilizadoras não se contam, então uma linha aqui significa que o alimento realmente acumula rótulos mais do que meramente ser mencionado muito.

Vale a pena ler antes de remover qualquer coisa. As listas nesta superfície foram cada uma escritas para uma pessoa diferente com um problema diferente, e convergem no mesmo grupo pequeno de alimentos densos em nutrientes. Satisfazê-las todas de uma vez produz uma dieta que ninguém desenhou e ninguém testou.

Falar com alguém que realmente pode testar

Nothing on this surface is personal medical advice. If a food genuinely makes you ill, if you have had a kidney stone or a gout attack, or if you are considering removing a food group from your diet, the person to talk to is your doctor, pharmacist or a registered dietitian — they can test for the things that can be tested for, which a table cannot.

Fontes:Autoridade Europeia para a Segurança dos Alimentos — parecer científico sobre glicoalcaloides em alimentos, em particular em batatas e produtos derivados. · O tecto informal de longa data de 200 mg/kg de glicoalcaloides totais em batata de mesa, usado na selecção de variedades há décadas. · Orientação nacional de armazenamento: mantenha as batatas no escuro, fresco e seco, e não refrigere.· Nomes de alimentos e ligações: a base de alimentos do sítio. Verificado2026-09-06.

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