New improved cassava recipe removes deadly ingredient
17 February 2007
MILLIONS of people in Africa depend on cassava for food despite an unfortunate bitter ingredient: cyanide.
Although cassava (Manihot esculenta) is processed to remove cyanide, the techniques are not always effective. Commonly the plant is ground into flour and then mixed in boiling water to create a claggy paste, but this only reduces cyanide levels by about 60 per cent. Consequently, each year thousands of children across central and east Africa are struck down by konzo, an irreversible paralysis of the legs. "Even in a good year in north Mozambique, cyanide levels [in cassava paste] frequently top 45 parts per million, far more than the WHO-recommended 10 ppm," says Howard Bradbury of the Australian National University in Canberra. Bradbury has now developed a simple technique for removing cyanide that could prevent much of the sickness. Cassava flour is mixed with water, and the dough spread in a layer no more than 1 centimetre thick, and left in the shade for 5 or 6 hours. The process removes almost all of the cyanide (Food Chemistry, vol 101, p 894).
It works by bringing together an enzyme in the plant cell walls with the cyanide-producing compound linamarin in the cytoplasm. The enzyme breaks down the linamarin, releasing hydrogen cyanide gas that then diffuses out.
[From issue 2591 of New Scientist magazine, 17 February 2007, page 16]