To Consider the toxicity of plants for humans those that humans frequently eat must be examined first. Many ordinary foods contain theoretically poisonous constituents, not as artificial or natural contaminants, but as part of their chemical make-up. This is incidentally quite separate from such known narcotics as tobacco, alcohol and tea and coffee. A review of natural toxins in foods- as in the list below-- might suprise some. - Wheat, rye, barley and oats contain a protein gluten that is hydrolysed in the digestive system to yield a peptidex-gliadin, a well-established and occasionally dangerous intestinal irritant.
- Lettuce contains in its sap a latex product, lactupicrin, that has many of the sedative and toxic properties of opium alkaloids.
- Apple seeds, and the kernels of apricots, plums and other stone fruits, as well as bitter almonds, contain significant quantities of cyanogenic glycosides that yield cyanide on hydrolysis, a process that also occurs in the digestive system.
- The cabbage family, which also includes mustard and horseradish, contains glucosilinates that yield goitre-causing thiocyanates and toxic nitriles.
- Potatoes are members of te deadly nightshade family: when the tuber turns green under the influence of the light it produces the same poisonous alkaloids.
- Many common household pulses, like soya bean, red kidney bean and haricot bean (as in baked beans), contain carious toxins, notable lectins called phytohaemagglutinins as well as trypsin-inhibitors, that can only reliably be neutralized by boiling for at least 30 minutes.
- The oil from rapeseed, widely grown in temperate climates as a cheap vegetable oil, contains erucic acid, which is known to cause heart damage in experimental animals.
The point of this list is not to alarm the public about the hidden dangers of eating. Of course, under almost all circumstances the food listed above are completely safe to eat. The real point is to show how difficult it is to predict the toxicity of a plant only from the presence of toxic constituents. As with other pharmacological questions, the action of the whole plant, and the way in which it is normally consumed, count for more than any individual constituent list. |
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