In an era of intensive farming and global trade, we take our food plants for granted. But if our ancient ancestors had not learned to deal with such natural poisons as a cyanide-producing compound in cassava, our modern diet would be severely restricted. Unfortunately, farmers in some places now neglect ancient wisdom.
So it is with cassava root, one of the most important food sources in tropical countries. It contains linamarin, a well-known cyanogen - a compound that produces cyanide when eaten. Rushing to get their crop to market, some farmers shortcut the traditional processing that removes linamarin. This puts millions of cassava eaters at risk for cyanide poisoning.
Enter modern genetic engineering to eliminate the problem at its root. Ohio State University in Columbus reports that plant biologists Richard Sayre and Dimuth Siritunga have created a cassava variety whose roots are essentially cyanogen free. Professor Sayre notes that this is particularly important for sub-Saharan Africa, where, he says, "improperly processed cassava is a major problem.... If we could eliminate the cyanogens in cassava, the plant wouldn't need to be processed before it's eaten."
Cassava is one of many common foods we eat without concern because centuries, even millenniums, of trial and error experience and cultivation have taught us how to make them wholesome.
Green potatoes contain toxic alkaloids. People learned long ago to peel off green skin and also any sprouts. When it comes to almonds, moderate consumption and careful processing are the best practice. Many fruit seeds also contain cyanogens. We learned to eat the apple and spit out the seeds. Traditional plant breeding has produced a lima bean - another cyanogen-bearing seed - with a low poison content. In fact, most beans naturally contain digestion-inhibiting chemicals, even cyanogens, until cooking renders them wholesome. Various spices also contain noxious compounds. Nutmeg is notorious for its hallucinogenic myristicin. People usually don't eat enough of any spice to cause health problems, except for thrill-seeking nutmeg "junkies."
Our food plants are descended from wild varieties that evolved defenses against plant-munching mammals and insects millions of years ago. What's poisonous to us is essential to the plant. Sayre says that in cassava, linamarin may be important in the transport of nitrogen from the plant's leaves to its roots. He says more research is needed to learn how restricting linamarin formation may affect plant yield and to develop commercially viable cyanogen-free varieties.
Cassava, also called manioc, originated in South America, where there is archaeological evidence for its use over many centuries. Proper processing involves boiling or soaking in water, baking, and drying.
Cassava spoils quickly when exposed to oxygen in air. Roots sold in American and European markets are coated with wax or wrapped in plastic to extend shelf life. These roots and tapioca, which is made from cassava, generally have been properly processed, Sayre says.
No one knows how long it took ancient food gathers and farmers to tame this nutritious yet dangerous plant. Today, biologists can rewrite a plant's genetic code to potentially turn it into a wholesome food source.