Cassava crisis: the deadly food that doubles as a vital Venezuelan crop

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It is a plant that millions depend on for survival. But another, identical range can be lethal and desperate people turning to the black market cant tell them apart

Venezuela has suffered food shortages for several years but things only seem to be getting worse. People are resorting to the black market for food, skipping snacks and rummaging through garbage in search of sustenance. Last year, three quarters of adults involuntarily lost an average of 19 lb ( 8.6 kg ). Malnutrition is on the rise and people are being exposed to lethal meat. At least 28 people have died as a result of eating bitter cassava, having mistaken it for the sweet variety.

Cassava, also known as manioc and yuca, is a staple food for about 700 million people worldwide. The perennial flower is native to South America but was brought to Africa by 17 th-century explorers and later introduced to Asia. It thrives in tropical climates. The flower is very resilient, living where many other crops fail, and involves less human investment per calorie than potatoes. It is often poorer communities that rely on cassava for their survival.

Both the leaves and the tubers of a cassava plant are supported in a wide range of foods. The tubers are similar to potatoes and can be prepared in much the same way: boiled, fried or mashed. In Venezuela in 2015, McDonalds outlets offered cassava fries when they couldnt get hold of potatoes. The tubers can also be ground into a flour, which can be used in cakes and bread. In the west, cassava is best known in the form of tapioca.

But this versatile, resilient harvest has one significant downside: raw, unprocessed cassava is the cause of cyanide.

All parts of the cassava plant contain cyanogenic glycosides that help protect it against pests. The cyanogenic glycosides lend a bitter savor that are typically puts off any casual grazers once they have taken the first bite. But the flower also has a backup plan to stop more determined herbivores. The cyanogenic glycosides can be rapidly processed by enzymes within the flower to release lethal hydrogen cyanide. The enzymes and glycosides are distinguished within the plant cells but if the tissue is injury, for example by little bit, the two mixture and rapidly liberated the toxic compound. Enzymes within the human gut can also liberate hydrogen cyanide from the cyanogenic glycosides if ingested.

Hydrogen cyanide disrupts the fundamental process of breathing within cells. Without energy, cells succumb rapidly and on a massive scale, leading to loss of life. Symptoms include vomiting, nausea, headaches and convulsions. Treatment is possible but must begin promptly, before irreversible injury is done.

It may seem extraordinary that such a potentially lethal plant would become the third most important harvest in the tropics. However, the protection against pests is an advantage when developing the crop and human ingenuity means that the tubers is also possible processed to bring the toxic content down to safe levels. The quantity of cyanogenic glycosides in the tubers varies greatly with flower range( from 50 mg of cyanide equivalent per kg up to 500 mg ), and is indicated by the bitterness of the tuber. It is the sweet diversities that are usually eaten and it is these that you would usually found under Venezuelan marketplaces.

The bitter assortments can be visually very similar to the sweet but involve careful processing to attain the flour safe to feed. Peeling, grating or grinding the tubers followed by soaking in sea causes the freeing and safe vapour of the hydrogen cyanide. The hour needed for soaking will vary according to local temperatures and the variety of cassava being prepared. As has been seen in Venezuela, preparing bitter cassava in the manner of a sweet diversity can have fatal consequences.

Humans do have some natural defence against the ingestion of cyanides. Rhodanese enzymes within the bodys cells add a sulfur atom to the cyanide unit, converting it from the highly toxic cyanide( CN ) to the much less toxic thiocyanate ion( SCN ). Normally a human could eat 30 -3 5mg of hydrogen cyanide from cassava without any ill impacts but problems occur if they are in poor health or if the influx of cyanide is sudden and greater than the detoxification system can cope with.

There are statutes in Venezuela proscribing the sale of bitter cassava roots for meat. But desperation increases and black markets develop, the chance of it being sold and feed in mistake for the sweet variety gets higher. Venezuelas troubled economy and food shortages are not expected to improve over the coming year. The last reported fatal cases of cassava poisoning occurred in February 2017. Lets hope these are the last.

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