Though we don’t consider enjoying a healthy square meal of kidney beans as a death-defying feat, it could actually be one!
Having uncooked or even improperly cooked kidney beans could be potentially lethal, and all of it has to do with the presence of a protein in the kidney beans called phytohemagglutinin(PHA). In fact, it’s not an uncommon protein. PHA is found in almost all leguminous seeds, but kidney beans happen to have a much higher concentration of phytohemagglutinin than other seeds.
Phytohemagglutinin
Phytohemagglutinin or PHA is a protein belonging to a class called lectins. Lectins are a group of proteins that help in binding carbohydrates, and scientists aren’t quite certain about the specifics of the function PHA serves in the bean plants, other than binding. But we do have a clear idea of what it does to the animal cells. It binds the red blood cells or erythrocytes together into a clump and is often used to separate the RBCs from the other blood constituents. It also interacts with different white blood cells and is used in Immunology research. The gist of things is that it does not do you any good if it enters your system.
PHA, if ingested, would line the mucosal cells of the alimentary canal and causes not only irritation, but also vomiting or diarrhea, and substantially reduce the absorption rate of nutrients through the digestive system. But this is just for starters, as it could further dissolve in blood and bundle up the erythrocytes, making them inefficient, as these clumps of cells could not move through the tiny capillaries. It could also interfere with the white blood cells and thus the immune system to varying degrees. The most alarming thing is that having just four or five uncooked or undercooked beans could cause these problems and throw our system out of balance. Though rarely it gets serious, most of the time, recovery takes place within 4-5 hours from the onset of symptoms.
All kidney beans are not killers though, if you take care to cook them till the boiling temperature. This is because PHA denatures on boiling, as its bonds break and becomes dysfunctional, thus harmless. Canned beans are not a problem, as they are boiled for safety before canning. But beans cooked in slow cookers, where they are cooked at lower temperatures for longer times, could be harmful, as the protein never reaches a temperature high enough to be denatured, and could be retained in the meal we enjoy.
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