Yam (vegetable) - Toxicity in Yams

Toxicity in Yams

Unlike cassava, most varieties of edible, mature, cultivated yam do not contain toxic compounds. However, there are exceptions.

Bitter compounds tend to accumulate in immature tuber tissues of white and yellow yams. These may be polyphenols or tanninlike compounds.

Wild forms of bitter yams do contain some toxins that taste bitter, and hence are referred to as bitter yam. Bitter yams are not normally eaten except at times of desperation in poor countries and in times of local food scarcity. They are usually detoxified by soaking in a vessel of salt water, in cold or hot fresh water or in a stream. The bitter compounds in these yams are water soluble alkaloids which, on ingestion, produce severe and distressing symptoms. Severe cases of alkaloid intoxication may prove fatal.

Aerial or potato yams too have antinutritional factors. In Asia, detoxification methods, involving water extraction, fermentation and roasting of the grated tuber are used for bitter cultivars of this yam. The bitter compounds in yams also known locally as air potato include diosbulbin and possibly saponins. These substances are toxic, causing paralysis. Extracts are sometimes used in fishing to immobolize the fish and thus facilitate capture. The community of Zulus use this yam as bait for monkeys, while hunters in Malaysia use it to poison wildlife such as tigers. In Indonesia an extract of air potato is used in the preparation of arrow poison.