Tongues can tell

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Tongues can tell

IITA, iNew

It may seem illogical to check for poison levels in cassava roots by tasting them, but a recent study in Malawi has proved that nibbling farmers know what they are doing.

The bitter sweet dilemma of cassava

Cassava is one of the most important staple crops for farmers in sub-Saharan Africa. Two main types grow in the region: one is used raw while the other has to be processed before eating. Local farmers in Nkhata Bay, Malawi refer to the groups as vyakuzizra (cool) and vyakubaba (bitter). But they can't always tell which is which just by looking at the plants.

Knowing the difference is vital as the "bitter" varieties have high levels of cyanogenic glucosides, an unpalatable form of cyanide, which can be harmful if ingested in large quantities. To check, farmers traditionally chew a small piece from the tip of the root; if it tastes bitter, the cassava needs to be detoxified through processing.

Although previous research in several countries has suggested a link between bitterness and toxicity in cassava, no one had previously tested the ability of farmers to predict the presence of glucosides based on taste. With funding from the Swedish International Development Agency and Uppsala University, a research team of Swedish, Danish, Malawian and IITA scientists investigated whether in fact there was a connection between a bitter taste and toxicity.

A trained sensory panel and a group of farmers from Malawi were asked to perform taste tests on the ten most commonly grown varieties of cassava, rating the flavor on a scale from "very bitter" to "very cool". The same roots were also analyzed to determine the exact concentration of cyanogenic glucosides.

For both tasting groups, there was a strong correlation between perceptions of bitterness and cyanogenic glucoside levels. Farmers were able to separate the varieties into groups and could further differentiate levels of toxicity among varieties in the "bitter" group. While the exact link between the two factors requires further study, for now farmers can continue trusting their tongues to make sure the food they prepare and sell continues to be safe to eat.

More information:

Article and image courtesy of i.New, International institute of tropical agriculture (IITA).

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August 2004	Article