Acetylcholinesterase inhibitors

Acetylcholinesterase inhibitors have been detected in several edible fruits and vegetables. Their active components are alkaloids. In many foodstuffs, however, they have not yet been identified. These include broccoli, Valencia oranges, sugar beet, cabbage, pepper, carrot, strawberry, apple, lima bean and radish. In potato, eggplant and tomato — members of the Solanaceae family — the principal alkaloids have been identified. The most potent inhibitors are found in potatoes, and of these the most active component is the glycoalkaloid solanine.

The toxicity of solanine has been the subject of extensive study. Oral administration results primarily in gastrointestinal and neurological symptoms.

The solanine concentration of potato tubers varies with the degree of maturity at harvest, rate of nitrogen fertilization, storage conditions, variety, and greening by exposure to light. Commercial potatoes contain 2 to 15 mg of solanine per 100 g fresh weight. Greening of potatoes may increase the solanine content to 80 to 100 mg per 100 g. Most of the alkaloid is concentrated in the skin. Sprouts may contain lethal amounts of solanine.

ch2oh

H HO

\S—C<T _ thioglucosidase _ "^N—O— SO- -► R — C=N—O — SO-

H OH Glucosinolate

Thiohydroxamate -O - sulfate r

R — N=C = S R — C=N R — S — C= N Isothiocyanate Nitrile Thiocyanate

The identities of R in the predominant glucosinolates of a number of vegetables:

The identities of R in the predominant glucosinolates of a number of vegetables:

Other brassicas, CH2=CH—CH2— Allyl horseradish, black mustard

Other brassicas, CH2=CH—CH2— Allyl horseradish, black mustard

Rape CH2=CH—CHOH — CH2— 2 - Hydroxybut - 3 - enyl

Rape CH2=CH—CHOH — CH2— 2 - Hydroxybut - 3 - enyl

General structures of glucosinolates and their hydrolysis products.

Since potatoes also contain other glycoalkaloids, namely chaconine and tomatine, with biological properties similar to solanine, the symptoms seen in potato poisoning may be due to combined actions of the alkaloids. All existing and newly developed varieties of potatoes are now monitored for alkaloid content. Solanine is heat stable and insoluble in water. Hence, toxic potatoes cannot be rendered harmless by cooking. It is generally accepted that 20 mg solanine per 100 g fresh weight is the upper safety limit.

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