Food Toxicology 2(2+0)

Lesson 13 : Animal Toxins and Plant Toxicants

Natural Plant table

Toxicant	Source	Action and symptoms
Goitrogens - goiter	Consumption of unusually large amounts of Brassica species, such as cabbage, broccoli, turnip, and mustard greens, might cause thyroid enlargement, but not if consumption is as a normal part of an otherwise adequate diet. Allyl isothiocyanates are a group of major naturally occurring compounds that confer a pungent flavor to foods, such as mustard and horseradish, where it is present at about 50 to 100 ppm.	Human goiter, related to iodine deficiency, is an important health problem in certain parts of the world. Goitrin is a goitrogenic substance formed from glucosinolate. Glucosinolates do not appear to be harmful until activated to isothiocynate, nitrile, and thiocyanate. Isothiocyanates and thiocynates have anti-thyroid activity. Goitrin formed from isothicyanate is a thyroid-suppressing substance. Isothiocyanates are toxic goitrogens which inhibit binding of iodine in the thyroid gland. Because iodine is required for the formation of the critical thyroid hormones thyroxine (T4) and triiodothyronine (T3), isothiocyanate-induced hyperthyroidism (goiter) mimics iodine deficiency. Hyperthyroidism is a physiological response as the thyroid attempts to compensate for reductions in both T4 and T3 Production. Endemic goiter is seen in geographical areas like India and Africa, where consumption of poorly processed foods is coincident with iodine deficiency. Normal processing steps (chopping, rinsing, milling) results in a safe product.
Cyanogenic Glycosides	Such compounds are natural herbicides and found in bitter almonds, kernels of cherries, apricots, and peach seeds; sorghum and related grasses; pulses, linseed, and cassava.	As few as 12 bitter almonds can potentially kill a small child. Cyanide in Foods Source Cyanide (mg/100 g) Sorghum (leaves, shoots) 60–240 Almond (kernel) 290 Apricot seed 60 Cassava 100 A lethal dose of cyanide is between 0.5 and 3.5 mg/kg body weight. The symptoms of acute cyanide intoxication are mental confusion, muscular paralysis, and respiratory failure. Thiosulfate plays a key role in detoxification of cyanide.
Phenolic substances	Phenolic substances contribute to the bitter taste, flavor, and color of foods. Phenolic Substance include Flavonoids, anthocyanidin, isoflavanone, Tannins, coumarin, safrole, myristicin, Capsaicin, d-Limonene Tannins are found in tropical fruits such as mangoes, dates, and in tea, coffee, grapes, wine, and cocoa. Black tea contains oxidized tannins Flavones are abundant and may contribute to the yellow pigments in plants. Coumarin, safrole, and myristicin are found as various flavor components. Myristicin is found in spices and herbs such as black pepper, carrot, parsley, celery Capsaicin is the extremely pungent ingredient (up to about 0.5%) in red and yellow chili peppers: d-Limonene is a major constituent of citrus oils and also is found, in much lower amounts, in other fruits and vegetables. The major sources of d-limonene are oils of orange, grapefruit, and lemon. Citrus peel oil can contain as much as 95% d-limonene & is used as flavoring agents in a variety of foods such as ice cream, soft drinks, baked goods, gelatin, chewing gum, and puddings. Purified coumarin was once used as a food additive, but this use was banned by the FDA after it was discovered that high doses caused liver damage in test animals. It also is used in human medicines as a blood thinning agent.	Condensed tannins are flavonoids. Tannins can tie up metals.. Tannins have been reported to cause liver injury (necrosis and fatty liver). Tannins bind proteins or cause precipitation of proteins, inhibiting digestive enzymes. They also reduce the bioavailability of iron In South Americans, the use of sorghum and heavy use of tannin rich teas may be responsible for esophageal cancers. Flavonoids have beneficial effects in preventing heart disease, particularly in populations with a high consumption of wine (French) and tea. Tea consumption has also been reported to protect against cardiovascular diseases. Gossypol is a toxic phenolic compound found in cottonseed. Gossypol consumption results in loss of appetite, weight loss, diarrhea, anemia, diminished fertility, pulmonary edema, circulatory failure, and hemorrhages of the GI tract. The phenolic compound inhibits the conversion of pepsinogen to pepsin and limits availability of iron. Topical creams containing capsaicin (0.025%) are commercially available as an analgesic. capsaicin prevents pain impulses from reaching the brain.
Caffeic Acid and Chlorogenic Acid	Caffeic and chlorogenic acid occur in an extremely wide range of fruits and vegetables. Caffeic acid and conjugates are present in high concentrations (over 1500 ppm) in many seasonings (thyme, basil, anise, caraway, marjoram); vegetables (lettuce, potatoes, radishes, and celery); and fruits (grapes, berries, eggplant, and tomatoes). Coffee is particularly rich in these phenolics, in addition to many other compounds. A cup of coffee contains about 190 mg of chlorogenic acid.	Caffeic acid inhibits 5-lipoxygenase which is a key enzyme in the biosynthesis of various eicosanoids,
Cholinesterase Inhibitors	Solanine is a anticholin-esterase toxicant found in foods like potato, particularly if the potato has been exposed to light, fungal infection, or bruising.	The enzyme cholinesterase aids in the hydrolysis of acetylcholine, a substance responsible for transmission of nerve impulse across the synapse. After the nerve impulse is transmitted, the acetylcholine must be hydrolyzed so that the neuron can become ready for the next impulse. Solanine is heat stable and insoluble in water; therefore, cooking does not remove the toxicant. The commercial potato has about 2 mg of solanine/100 g, and greening increases the content to 50 to 100 mg/100 g. The FDA regulates the solanine content to be no more than 20 mg/100 g.
Biogenic Amines	Dopamine and tyramine are natural components of banana, cheese, and avocado, and bacterial action on the amino acids found in meats and fish. Some specific examples include the fava bean. Tyramine content can be high in oriental preserved foods such as soy sauce, soybean paste, and various condiments. Swiss cheese has been implicated in outbreaks of histamine poisoning.	Histamine has been implicated as etiological agents in several outbreaks of food poisoning. Norepinephrine and dopamine or catecholamines are pressor amines important as neutrotransmitters. Spanish wines have been shown to increase histamine and tyramine content within 5 d of manufacturing.. Hypertension, palpitations, and severe headaches are common. In some cases, intracranial bleeding can occur, leading to death. Foods containing large amounts of biogenic amines are counter-indicated in patients using MAO inhibitors, such as antidepressants
Hydrazine’s and Other	Edible Mushrooms. All contain substantial amounts of compounds in the hydrazine family, many of which are potent liver toxins and carcinogens.	People consuming a 100 g serving and, therefore, ingesting 50 mg would be getting very nearly the same dose on a per kilogram (kg) body weight basis as that giving cancer to mice upon sustained daily exposure. Whole mushrooms have been shown in numerous studies to cause cancer in laboratory animals, but whether they are a significant cause of cancer in people is uncertain.