Foods are regarded as such because they are palatable and have nutritional value; otherwise there would be no point in consuming them. However, many foods do contain toxins as a naturally-occurring constituent or, are formed as the result of handling or processing, but the risk for toxicity due to consumption of naturally occurring food toxins is fairly low. Nowadays the consumer’s attention is so focused upon synthetic contaminants and food additives that the harmful effects of naturally occurring toxins are often overlooked.
Natural toxins in food are considered important food safety issues of growing concern. Naturally occurring toxic constituents are usually present in doses that are too small to produce harmful effects when foods are eaten normally, except in the cases of consumers who may be sensitive to individual ingredients. So the significance of naturally occurring toxins in the human diet should not be underestimated as they may have deleterious effect on human health either acutely or after chronic intake.
These are some of the foods that contain natural toxins
Natural toxins present in foods of plant origin (plant toxins)
Red Kidney Beans(rajma)
Dried red kidney beans contain natural toxin called Lectin(Phytohaemagglutinins) which can cause stomach aches and vomiting. These can be destroyed if you soak these dried beans in water for at least 12 hours and then cook thoroughly at boiling temperature. Tinned Beans are safe to eat without further cooking as they have already been processed so can be used without further treatment.
Soybeans contain a natural toxin called trypsin inhibitors and that inhibits the activity of the digestive enzymes trypsin and chymotrypsin in the gut, thus preventing protein digestion. These inhibitors are proteins and are therefore denatured and inactivated by cooking. These will not cause problems in humans if legumes (soybeans) are cooked at boiling temperature after thorough soaking in water. Although feeding raw legumes to animals can result in pancreatic enlargement
Green and sprouted Potatoes
All potatoes contain natural toxins called glycoalkaloids, usually at low levels and Solanine is one of a range of heat stable glycoalkaloid compound found in green part of the potato plant. A very high levels of this glycoalkaloid can be found in green part of potatoes, sprouted potatoes and potatoes stored in light. These glycoalkaloids possess anticholinesteraseactivity which can produce gastrointestinal and neurological disorders. Severe glycoalkaloid poisoning is very rare, but it’s important to store potatoes in a dark, cool and dry place and not to eat green and sprouted parts and it is also advisable to keep smaller stock at one time.
Parsnips (Muli, Gajar, Chukandar)
Parsnips release toxins known as furocoumarins when exposed to harsh weather conditions. They are also present in lower concentration in other foods such as citrus fruits. Side effects associated with furocoumarins poisoning are stomach ache and painful skin reaction if person is exposed to increased amount of UV light during consumption of the poisonous plant. Since highest concentration of toxins is found in peel and surface layer, plant should be peeled and all damaged parts should be removed before cooking. Level of toxins will drop during cooking, boiling or preparing the plant in the microwave. Cooking water should be thrown away.
Mouldy and damaged apples may contain a toxin called patulin. Frequently it is found in apple products such as juices, jams and ciders. Fungal growth leading to patulin production is most common on damaged fruits. Any fruit with visible signs of rotting, decay or mold growth can be suspected and contain patulin. Patulin is stable in apple juice, so removal of contaminated apples from the initial processing lines during apple juice production has to be considered seriously. It is advised not to eat mouldy or damaged apples and not to use the contaminated apples to make apple sauces or juice
Rhubarb contains oxalic acid, a toxic substance that in high enough concentrations can cause stomach irritation and kidney problem. It can also mess up the body’s calcium metabolism and leach calcium from the body. Highest levels of oxalic acid are located in the plant’s leaves and they should not be eaten. In case one eats plant with too much oxalic acid, one may experience muscle twitching and cramping, respiratory difficulties, bradycardia, pain, vomiting, convulsion and even coma. Trim the leaves immediately from the stalk and wash the stalk well before eating. Distilling the oxalic acid from rhubarb leaves into water and adding calcium carbonate removes oxalic acid, then it can be strained from the mixture.
Zucchini ( Turee)
Zucchini also called courgette, has its origin in America and is available in yellow, light green, and green color. The shape of this small summer squashresembles that of a ridged cucumber and features numerous seeds. Even though zucchini is a fruit, it is usually cooked as a vegetable because it is best when eaten in cooked dishes. Zucchini may however contain toxins known as cucurbitacins. These toxins are often seen in wild plants and rarely in commercially available vegetable. Since toxins give zucchini a bitter taste, you can detect uneatable vegetable by taste and strong odor. Cucurbitacins can induce vomiting, stomach cramps and diarrhea. It is advisable to desiccate the Zucchini before cooking or eating as raw, as it removes cucurbitacins. Putting the zukes in salt water and then straining it is also recommended.
Giotrogenic foods (Cabbage, Cauliflower, Broccoli, Mustard Radishes, and Turnip)
The cruciferous vegetable foods contain a number of glucosinolate and thiocyanate compounds that interfere with normal utilization of iodine by the thyroid gland and can result in goitre. Just because these foods are high in goitrogens doesn’t mean we should avoid eating them, but we should avoid these foods in their raw form, as cooking helps reduce the goitrogenic substances
Mushrooms are an important component of human diet and some mushrooms are popular worldwide for their nutritional and therapeutic properties. However, some species are dangerous because of toxicity. Mushroom toxins have been divided into various categories as Amatoxins, Gyromitrin, Muscarine, and Phallotoxins. The toxic versions include Death cap mushrooms, Inocybe mushrooms, Cortinarius mushrooms, and Magic mushrooms. Cases of serious human poisoning generally are caused by the improper identification of toxic mushroom species. Mushroom poisoning can cause adverse effects such as liver failure, bradycardia, chest pain, seizures, gastroenteritis, intestinal fibrosis, renal failure, erythromelalgia, and rhabdomyolysis. Most of the toxins in wild mushrooms cannot be destroyed by heat so it is advisable not to pick or consume wild mushrooms
Cyanogenic plants (Bitter apricot seeds, Bamboo shoots, Cassava and Flaxseeds)
Cyanogenic glycosides (amygdalin, prunasin, dhurrin, linamarin) are present in some of these plants in raw state, with releasable cyanide. The toxicity of cyanogenicglucosides and their derivatives is dependent on the release of hydrogen cyanide. Dietary exposure to elevated levels of some cyanogenic glycosides in food has the potential to cause acute cyanide poisoning or a debilitating irreversible neurological condition in the long term. Children are particularly at risk because of their smaller body size. It is recommended that cyanogenic plants should be peeled and cut into smaller pieces and cooked thoroughly to release toxic hydrogen cyanide before consumption in order to reduce the level of the toxin. Also, seeds of fruits to be processed into juice should be removed before crushing to avoid cyanide poisoning.
Tannins are a broad class of compounds that is present in tea, red wine, cocoa, chocolates, coffee, broad beans, some herbal preparations, grapes and certain fruits like blackberries, and cranberries. Tannins inhibit the absorption of iron and in children with low iron intakes, regular consumption of these foods have been seen to be associated with anemia. High levels of tea consumption may contribute to low iron status in people with marginal iron intakes.
The part II of the article would appear in next edition
STO Kashmir, DHS Kashmir
Former Director with FSSAI New Delhi