PHA is known to be an insecticide, and plants probably developed it to keep their seeds from being destroyed by pests. In humans and other susceptible mammals (those of us without compound stomachs) PHA attacks and disables the epithelial cells lining the intestine. The body reacts to the threat by emptying the entire digestive tract as rapidly and completely as possible, to rid itself of the toxic substance...

Gardeners, in particular, should be a aware of the potential dangers of raw beans if they like to "graze" in their gardens, eating the fresh raw seeds directly from the shell. The level of PHA in all varieties is not known.
Green beans (snap beans) are a questionable matter. Many people do like to eat young green beans raw, and overcooking green beans until mushy is widely regarded as a sin against the vegetable. I can find no clear evidence that raw green beans have PHA levels high enough to make them unsafe for most of the population. It should be noted that the level of PHA is highest in seeds, and green beans are usually consumed for the sake of the green fleshy pod, at a stage when the seeds are only beginning to develop.
And from another source:
The syndrome is usually caused by the ingestion of raw, soaked kidney beans, either alone or in salads or casseroles. As few as four or five raw beans can trigger symptoms. Several outbreaks have been associated with "slow cookers" or crock pots, or in casseroles which had not reached a high enough internal temperature to destroy the glycoprotein lectin. It has been shown that heating to 80 degrees C. may potentiate the toxicity five-fold, so that these beans are more toxic than if eaten raw. In studies of casseroles cooked in slow cookers, internal temperatures often did not exceed 75 degrees C.
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