Below is a detailed analysis of the anti-nutrient composition of different plant foods, showing why the majority of them can be inflammatory to anyone in high amounts, and to those particularly sensitive in low amounts.
|Phytic acid||Bran of grains and pseudo-grains, all kind of seeds, nuts, legumes, potatoes.||Birds and ruminant animals: phytase enzyme. Partially by soaking, cooking, fermenting, sprouting.||Binding with minerals of food in the gut: deficiency of iron, zinc, calcium and other minerals. Reduces the digestibility of starches, proteins, and fats.|
|Lectins||Grains, pseudo-grains, seeds, nuts, legumes, nightshade vegetables, diary, eggs.||Cooking with seaweeds and mucilaginous vegetables (okra). Partially by soaking, boiling in water, fermenting, sprouting.Wheat, soy, peanuts and dried beans are the most resistant to neutralization.||Leaky gut, neurodegenerative disease, inflammatory diseases, infectious and autoimmune diseases, blood clotting.|
|Saponins||Legumes, pseudo-grains, potatoes, red wine.||Different results in studies for soaking, cooking and fermentation. Cholesterol and bile.||Leaky-gut, disturbs digestive enzymes.|
|Oligosaccharides||Legumes||Other animals: alpha-galactosidase. Sprouting, fermentation. Bacteria in the colon.||Gas production.|
|Oxalates||Grains bran, nuts, soy, spinach, rhubarb, swisschard, chocolate, black tea, some fruits and vegetables. Metabolite of fungus and dysbiotic flora. Metabolism of the amino acids glycine and serine, vitamin C and sugar.||Partially by cooking.||Binding with calcium: Calcium and magnesium deficiency, kidney stones, disturb digestive enzymes. Hyperoxaluria may play a significant role in autism, COPD/asthma, thyroid disease, fibromyalgia, interstitial cystitis, vulvodynia, depression, arthritis. Researchers believed that “Oxalate hyperabsorptionmay be the main reason for stone formation in more than half of the idiopathic calcium oxalate stone formers”.|
|Cyanide||Beans, manioc, and many fruit pits (such as apricot kernels and apple seeds).||Cooking and phase II liver detox.||Cerebral damage and lethargy.|
|Canavanine||Alfalfa sprout.||Cooking and phase II liver detox and kidneys.||Abnormal blood cell counts, spleen enlargement, Lupus (if big amount of juice sprouts is taken).|
|Goitrogens||Soy, peanuts and cruciferous vegetables.||Cooking, fermenting.||Hypothyroidism.|
|Tannins||Legumes, some fruits and vegetables, tea, chocolate, wine, coffee, vinegar.||Tannin-binding salivary proteins. Partially by soaking and cooking. About 90% by germination.||Zinc and iron deficiency, decrease in both growth rate and body weight gain, perturbation of mineral absorption, inhibition of digestive enzymes, accelerate blood clotting, produce liver necrosis.|
|Trypsin inhibitor||Grains and legumes.||Partially by cooking, sprouting.||Growth inhibition and pancreatitis.|
|Alpha-amylase inhibitor||Grains, legumes, nuts skin, stevia leaves.||Partially by cooking, sprouting.||Dysbiosis (candidiasis). Deleterious histological changes to the pancreas.|
|Allicin and mustard oil||Onions, shallots, leeks, chives, scallions, and garlic.||Cooking and phase II liver detox.||Bad breath, and bad body odor, indigestion, acid reflux, diarrhea, stomach pain, gas, anemia, reduced blood clotting of open wounds., allergic reactions, accidental abortions in humans. Disturbs a baby’s ability to breast feed.|
|Salicylates||Berries and dried fruits, some vegetables, herbs and spices.||Sulfotransferase enzyme.||Same as medicines (aspirin): bleeding of the stomach and gastrointestinal tract, dyspepsia, skin reactions, liver toxicity, prolonged bleeding time, impaired kidney function, dizziness, mental confusion, allergic reactions.|
|Calcitriol, solanine, nicotine||Green potatoes, egg plant, peppers, tomatoes, goji berries.||Liver and kidneys.||Calcinosis, muscle pain and tightness, morning stiffness, poor healing, arthritis, insomnia gall bladder problems.|
|Gluten||All wheat, rye and barley plants.||Digestive problems, leaky gut syndrome or autoimmune disease, allergic reactions, and cognitive problems.|
|Chaconine||Corn and plants of the Solanaceae family.||Partially by cooking.||Digestive issues.|
|Fiber||All natural and unprocessed plants and mushrooms||Diverticular disease, constipation, haemorrhoids, bloating, anal bleeding, abdominal pain, leaky gut syndrome, inflammatory bowel diseases, a host of other autoimmune diseases, bowel cancer, depletes vitamins and minerals from the body|
|Endocrine Disruptors||Foods||Negative Effects|
|Phytoestrogens||Soybeans and soy products, tempeh, linseed (flax), sesame seeds, wheat berries, fenugreek (contains diosgenin, but also used to make Testofen®, a compound taken by men to increase testosterone). oats, barley, beans, lentils ,yams, rice, alfalfa, mung beans, apples, carrots, pomegranates, wheat germ, rice bran, lupin, kudzu, coffee, licorice root, mint, ginseng, hops, bourbon whiskey, beer, fennel and anise, red clover (sometimes a constituent of green manure).||Accelerated aging process, androgen hormone imbalances, autoimmune disorders such as lupus, breast tenderness, cervical dysplasia, difficultly losing weight, early onset of menstruation, endocrine imbalances, low male sex hormones, fibrocystic breasts, fibromyalgia, gynecomastia (or “man boobs”), infertility in men and women, irregular menstrual periods, low sperm count, low sex drive/libido, endometriosis|
|Exorphins||Gluten-containing cereals are a main food staple present in the daily human diet, including wheat, barley, and rye.||Gluten intake is associated with the development of celiac disease (CD) and related disorders such as diabetes mellitus type I, depression, and schizophrenia. However, until now, there is no consent about the possible deleterious effects of gluten intake because of often failing symptoms even in persons with proven CD. Asymptomatic CD (ACD) is present in the majority of affected patients and is characterized by the absence of classical gluten-intolerance signs, such as diarrhea, bloating, and abdominal pain. Nevertheless, these individuals very often develop diseases that can be related with gluten intake. Gluten can be degraded into several morphine-like substances, named gluten exorphins. These compounds have proven opioid effects and could mask the deleterious effects of gluten protein on gastrointestinal lining and function. Here we describe a putative mechanism, explaining how gluten could mask its own toxicity by exorphins that are produced through gluten protein digestion. The precise pathway leading to the development of ACD still needs to be discovered. However, the putative mechanism presented in this review could explain this intruding phenomenon. The incomplete breakdown of the gluten protein, resulting in the presence of gliadin peptides with opioid effects, makes it plausible to suggest that the opioid effects of gluten exorphins could be responsible for the absence of classical gastrointestinal symptoms of individuals suffering from gluten-intake-associated diseases. Moreover, the partial digestion of gluten, leading to DPP IV inhibition, could also account for the presence of extra-intestinal symptoms and disorders in ACD and the occurrence of intestinal and extra-intestinal symptoms and disorders in CD and NCGS patients. If so, then individuals suffering from any of these conditions should be recognized in time and engage in a gluten-free lifestyle to prevent gluten-induced symptoms and disorders.|
|Immune Disruptors||Foods||Negative Effects|
|Gliadin||Barley, buckwheat, durum wheat, bulgur, wheat bran, wheat germ, triticale, quinoa, millet, spelt and teff.||Incidentally, antibodies to gliadin are capable of binding to nervous system tissue and may contribute to immune-mediate neurological impairment, such as cerebellar ataxia and gluten encephalopathy. Gliadin, particular the omega fraction, is also responsible for allergic responses, including Bakers’ asthma and the odd wheat-dependent, exercise-induced analyphylaxis (WDEIA).)|
|Thaumatin-Like Proteins||Fruits, wheat, vegetables nuts etc…||Allergies, stimulate immune system or disrupt physical barriers|
|DNA/RNA Binding Molecules||Foods||Negative Effects|
|Rice miRNA||Rice||Alter transcription of LDL-receptor|
Bruce Ames is the inventor of the Ames test, a system for easily and cheaply testing the mutagenicity of compounds.
The toxicological significance of exposures to synthetic chemicals is examined in the context of exposures to naturally occurring chemicals. It is calculated that 99.99% (by weight) of the pesticides in the American diet are chemicals that plants produce to defend themselves. Only 52 natural pesticides have been tested in high-dose animal cancer tests, and about half (27) are rodent carcinogens; these 27 are shown to be present in many common foods. It is concluded that natural and synthetic chemicals are equally likely to be positive in animal cancer tests. It is also concluded that at the low doses of most human exposures the comparative hazard synthetic pesticide residues are insignificant.
Concentrations of natural pesticides in plants are usually measured in parts per thousand or million (16-23) rather than parts per billion, the usual concentration of synthetic pesticide residues or of water pollutants (1, 24). It is estimated that humans ingest roughly 5000 to 10,000 different natural pesticides and their breakdown products (16-23). For example, Table 1 shows 49 natural pesticides (and metabolites) that are ingested when cabbage is eaten, and indicates how few have been tested for carcinogenicity or clastogenicity. Lima beans contain a completely different array of 23 natural toxins that, in stressed plants, range in concentration from 0.2 to 33 parts per thousand fresh weight; none appears to have been tested yet for carcinogenicity or teratogenicity (19). Many Leguminosae contain canavanine, a toxin arginine analog that, after being eaten by animals, is incorporated into protein in place of arginine. Feeding alfalfa sprouts (1.5% canavanine dry weight) or canavanine to monkeys causes a lupus erythema- tosus-like syndrome (44). Lupus in humans is characterized by a defect in the immune system that is associated with autoimmunity, anti-nuclear antibodies, chromosome breaks, and various types of pathology. The toxicity of nonfood plants is well known: plants are among the most commonly ingested poisonous substances for children under 5 years. Surprisingly few plant toxins have been tested for carcinogenicity (10-13, 45). Among 1052 chemicals tested in at least one species in chronic cancer tests, only 52 are naturally occurring plant pesticides (10-13). Among these, about half (27/52) are carcinogenic. 11 Even though only a tiny proportion of the plant toxins in the human diet have been tested so far, the 27 natural pesticides that are rodent carcinogens are present in the following foods: anise, apple, apricot, banana, basil, broccoli, brussels sprouts, cabbage, cantaloupe, caraway, carrot, cauliflower, celery, cherries, cinnamon, cloves, cocoa, coffee, collard greens, comfrey herb tea, currants, dill, eggplant, endive, fennel, grapefruit juice, grapes, guava, honey, honeydew melon, horseradish, kale, lentils, lettuce, mango, mushrooms, mustard, nutmeg, orange juice, parsley, parsnip, peach, pear, peas, black pepper, pineapple, plum, potato, radish, raspberries, rosemary, sesame seeds, tarragon, tea, tomato, and turnip. Thus, it is probable that almost every fruit and vegetable in the supermarket contains natural plant pesticides that are rodent carcinogens. The levels of these 27 rodent carcinogens in the above plants are commonly thousands of times higher than the levels of synthetic pesticides. Table 2 shows a variety of natural pesticides that are rodent carcinogens occurring in the parts-per-million range in plant foods. The catechol-type phenolics, such as tannins, and caffeic acid and its esters (chlorogenic and neochlorogenic acids), are more widespread in plant species than other natural pesticides (e.g., Tables 1 and 2).
Dietary Pesticides Are 99.99% All Natural. Nature’s pesticides are one important subset of natural chemicals. Plants produce toxins to protect themselves against fungi, insects, and animal predators (5, 16-23). Tens of thousands of these natural pesticides have been discovered, and every species of plant analyzed contains its own set of perhaps a few dozen toxins. When plants are stressed or damaged, such as during a pest attack, they may greatly increase their natural pesticide levels, occasionally to levels that can be acutely toxic to humans. We estimate that Americans eat about 1.5 g of natural pesticides per person per day, which is about 10,000 times more than they eat of synthetic pesticide residues (see below). As referenced in this paper (see refs. 16-21 and legends to Tables 1 and 2), there is a very large literature on natural toxins in plants and their role in plant defenses. The human intake of these toxins varies markedly with diet and would be higher in vegetarians. Our estimate of 1.5 g of natural pesticides per person per day is based on the content of toxins in the major plant foods (e.g., 13 g of roasted coffee per person per day contains about 765 mg of chlorogenic acid, neochlorogenic acid, caffeic acid, and caffeine; see refs. 22 and 23 and Table 2). Phenolics from other plants are estimated to contribute another several hundred milligrams of toxins. Flavonoids and glucosinolates account for several hundred milligrams; potato and tomato toxins may contribute another hundred, and saponins from legumes another hundred. Grains such as white flour and white rice contribute very little, but whole wheat, brown rice, and corn (maize) may contribute several hundred milligrams more. The percentage of a plant’s weight that is toxin varies, but a few percent of dry weight is a reasonable estimate: e.g., 1.5% of alfalfa sprouts is canavanine and 4% of coffee beans is phenolics. However, the percentage in some plant cultivars is lower (e.g., potatoes and tomatoes).
Table 1. There are forty-nine natural pesticides and metabolites found in cabbage alone
|Food||Pesticides and Metabolites|
|Cabbage||Glucosinolates: 2-propenyl glucosinolate (sinigrin),* 3-methylthiopropyl glucosinolate, 3-methylsulfinylpropyl glucosinolate, 3-butenyl glucosinolate, 2-hydroxy-3-butenyl glucosinolate, 4-methylthiobutyl glucosinolate, 4-methylsulfinylbutyl glucosinolate, 4-methylsulfonylbutyl glucosinolate, benzyl glucosinolate, 2-phenylethyl glucosinolate, propyl glucosinolate, butyl glucosinolate Indole glucosinolates and related indoles: 3-indolylmethyl glucosinolate (glucobrassicin), 1-methoxy-3-indolylmethyl glucosinolate (neoglucobrassicin), indole-3-carbinol,* indole-3-acetonitrile, bis(3-indolyl)methane Isothiocyanates and goitrin: allyl isothiocyanate,* 3-methylthiopropyl isothiocyanate, 3-methylsulfinylpropyl isothiocyanate, 3-butenyl isothiocyanate, 5-vinyloxazolidine-2-thione (goitrin), 4-methylthiobutyl isothiocyanate, 4-methylsulfinylbutyl isothiocyanate, 4-methylsulfonylbutyl isothiocyanate, 4-pentenyl isothiocyanate, benzyl isothiocyanate, phenylethyl isothiocyanate Cyanides: 1-cyano-2,3-epithiopropane, 1-cyano-3,4-epithiobutane, 1-cyano-3,4-epithiopentane, threo-1-cyano-2-hydroxy-3,4-epithiobutane, erythro-1-cyano-2-hydroxy-3,4-epithiobutane, 2-phenylpropionitrile, allyl cyanide,* 1-cyano-2-hydroxy-3-butene, 1-cyano-3- methylsulfinylpropane, 1-cyano-4-methylsulfinylbutane Terpenes: menthol, neomenthol, isomenthol, carvone* Phenols: 2-methoxyphenol, 3-caffoylquinic acid (chlorogenic acid),* 4-caffoylquinic acid,* 5-caffoylquinic acid (neochlorogenic acid),* 4-(p-coumaroyl)quinic acid, 5-(p-coumaroyl)quinic acid, 5-feruloylquinic acid|
*Discussed below; all others untested. Clastogenicity. Chlorogenic acid (25) and allyl isothiocyanate are positive (26). Chlorogenic acid and its metabolite caffeic acid are also mutagens (27-29), as is allyl isothiocyanate (30). Carcinogenicity. Allyl isothiocyanate induced papillomas of the bladder in male rats (a neoplasm that is unusually rare in control rats) and was classified by the National Toxicology Program as carcinogenic. There was no evidence of carcinogenicity in mice; however, it was stated “the mice probably did not receive the MTD” (31, 32). Sinigrin (allyl glucosinolate, i.e., thioglycoside of allyl isothiocyanate) is cocarcinogenic for the rat pancreas (33). Carvone is negative in mice (34). Indole-3-acetonitrile has been shown to form a carcinogen, nitroso indole acetonitrile, in the presence of nitrite (35). Caffeic acid is a carcinogen (36, 37) and clastogen (25) and is a metabolite of its esters 3-, 4-, and 5-caffoylquinic acid (chlorogenic and neochlorogenic acid). Metabolites. Sinigrin gives rise to allyl isothiocyanate when raw cabbage (e.g., coleslaw) is eaten; in cooked cabbage it also is metabolized to allyl cyanide, which is untested. Indole-3-carbinol forms dimers and trimers on ingestion, which mimic dioxin. Occurrence. See refs. 18, 21, and 38-40. Toxicology. The mitogenic effects of goitrin (which is goitrogenic) and various organic cyanides from cabbage suggest that they may be potential carcinogens. Aromatic cyanides related to those from cabbage have been shown to be mutagens and are metabolized to hydrogen cyanide and potentially mutagenic aldehydes.
The cooking of food is also a major dietary source of potential rodent carcinogens. Cooking produces about 2 g (per person per day) of mostly untested burnt material that contains many rodent carcinogens-e.g., poly- cyclic hydrocarbons (81, 91), heterocyclic amines (92, 93), furfural (22, 23), nitrosamines and nitroaromatics (1, 94)-as well as a plethora of mutagens (91-95). Thus, the number and amounts of carcinogenic (or total) synthetic pesticide resi- dues appear to be minimal compared to the background of naturally occurring chemicals in the diet. Roasted coffee, for example, is known to contain 826 volatile chemicals (22); 21 have been tested chronically and 16 are rodent carcinogens (10-13); caffeic acid, a nonvolatile rodent carcinogen, is also present (Table 2). A typical cup of coffee contains at least 10 mg (40 ppm) of rodent carcinogens (mostly caffeic acid, catechol, furfural, hydroquinone and hydrogen peroxide) (Table 2). The evidence on coffee and human health has been recently reviewed, and the evidence to date is insufficient to show that coffee is a risk factor for cancer in humans (81, 86). The same caution about the implications for humans of rodent carcinogens in the diet that were discussed above for nature’s pesticides apply to coffee and the products of cooked food. Clastogenicity and Mutagenicity Studies. Results from in vitro studies also indicate that the natural world should not be ignored and that positive results are commonly observed in high-dose protocols. Ishidate et al. (26) reviewed experi- ments on the clastogenicity (ability to break chromosomes) of 951 chemicals in mammalian cell cultures. Of these 951 chemicals, we identified 72 as natural plant pesticides, and 35 (48%) were positive for clastogenicity in at least one test. This is similar to the results for the remaining chemicals, of which 467/879 (53%) were positive in at least one test. Of particular interest are the levels at which some of the carcinogenic plant toxins in Table 2 were clastogenic (26). Allyl isothiocyanate was clastogenic at a concentration of 0.0005 ppm, which is about 200,000 times less than the concentration of sinigrin, its glucosinolate, in cabbage. Allyl isothiocyanate was among the most potent chemicals in the compendium (26) and is also effective at unusually low levels in transforming (96) and mutating (30) animal cells. (See also the discussion of cancer tests in Table 1.) Safrole was clastogenic at a concentration of about 100 ppm, which is 30 times less than the concentration in nutmeg and roughly equal to the concentration in black pepper. The rodent carcinogens safrole and estragole, and a number of other related dietary natural pesticides that have not been tested in animal cancer tests, have been shown to produce DNA adducts in mice (97). Caffeic acid was clastogenic at a concentration of 260 and 500 ppm, which is less than its concentration in roasted coffee beans and close to its concentration in apples, lettuce, endive, and potato skin. Chlorogenic acid, a precursor of caffeic acid, was clastogenic at a concentration of 150 ppm, which is 100 times less than its concentration in roasted coffee beans and similar to its concentration in apples, pears, plums, peaches, cherries, and apricots. Chlorogenic acid and caffeic acid are also mutagens (Table 1). Coffee is genotoxic to mammalian cells (98). Plant phenolics such as caffeic acid, chlorogenic acid, and tannins (esters of gallic acid) have been reviewed for their mutagenicity and antimutagenicity, clas- togenicity, and carcinogenicity (99).
Some natural pesticide carcinogens in food
|Rodent Carcinogen||Concentration in Part per Million||Foods|
|5-/8-Methoxypsoralen||0.8-32||Parsley, parsnip, celery|
|Sinigrin*(allyl isothiocyanate)||12-72,000||Cabbage, collard greens, cauliflower, brussels sprouts, mustard (brown), horseradish|
|D-Limonene||31-8,000||Orange juice, mango, black pepper|
|Safrole||100-10,000||Nutmeg, mace, black pepper|
|Sesamol||75||Sesame seeds (heated oil)|
|Benzyl acetate||15-230||Honey, basil, jasmine tea|
|Catechol||100||Coffee (roasted beans)|
|Caffeic acid||50-1,800||Apple, carrot, celery, cherry, eggplant, endive, grapes, lettuce, pear, plum, potato, absinthe, anise, basil, caraway, dill, marjoram, rosemary, sage, savory, tarragon, thyme, coffee (roasted beans)|
|Chlorogenic acid† (caffeic acid)||50-21,600||Apricot, cherry, peach, plum, coffee (roasted beans)|
|Neochlorogenic acid† (caffeic acid)||50-11,600||Apple, apricot, broccoli, brussels sprouts, cabbage, cherry, kale, peach, pear, plum, coffee (roasted beans)|
Carcinogen tests are referenced in refs. 10-13 and the following: 5-methoxypsoralen (light-activated) and 8-methoxypsoralen (46, 47) (psoralen, which is carcinogenic by skin painting, and many other mutagenic psoralen derivatives are also present in parsley and celery); p-hydrazinobenzoate and glutamyl p-hydrazinobenzoate (48, 49); allyl isothiocyanate (31, 32); D-limonene (50); estragole and safrole (45, 51); ethyl acrylate and benzyl acetate (52); a-methylbenzyl alcohol (53); caffeic acid (37); sesamol (37); catechol (37). Concentration references are as follows: 5- and 8-methoxypsoralen (17, 55-59); p-hydrazinobenzoates (in commercial mushrooms) (48, 49); sinigrin (38-40, 60); D-limonene (61-63); estragole and safrole (64-67); ethyl acrylate (68); benzyl acetate (69-71), a-methylbenzyl alcohol (23); caffeic acid, chlorogenic acid, and neochlorogenic acid (72-80) [in coffee (81)]; catechol (83, 84); sesamol (85). For mutagenicity and clastogenicity references, see text.
*Sinigrin is a cocarcinogen (33) and is metabolized to the rodent carcinogen allyl isothiocyanate, although no adequate test has been done on sinigrin itself. The proportion converted to allyl isothiocyanate or to allyl cyanide depends on food preparation (38-40).
†Chlorogenic and neochlorogenic acid are metabolized to the carcinogens caffeic acid and catechol (a metabolite of quinic acid) but have not been tested for carcinogenicity themselves. The clastogenicity and mutagenicity of these compounds are referenced in Table 1.
It is probable that almost every fruit and vegetable in the supermarket contains natural plant pesticides that are rodent carcinogens. The levels of these 27 rodent carcinogens in the above plants are commonly thousands of times higher than the levels of synthetic pesticides.
Abstract: Compounds or substances which act to reduce nutrient intake, digestion, absorption and utilization and may produce other adverse effects are referred to as antinutrients or antinutritional factors. Seeds of legumes and other plant sources contain in their raw state wide varieties of antinutrients which are potentially toxic. The major antinutrients includes: toxic amino acids, saponins, cyanogenic glycosides, tannins, phytic acid, gossypol, oxalates, goitrogens, lectins (phytohaemagglutinins), protease inhibitors, chlorogenic acid and amylase inhibitors. These antinutrients pose a major constraint in the use of plant protein sources in livestock feeds without adequate and effective processing. The level or concentration of these anitnutrients in plant protein sources vary with the species of plant, cultivar and post-harvest treatments (processing methods). This paper reviews the nutritional effect of major antinutrients present in plant protein sources. Key words: Antinutrients, plant protein, legumes
INTRODUCTION Antinutrients or antinutritional factors may be defined as those substances generated in natural feedstuffs by the normal metabolism of species and by different mechanisms (for example inactivation of some nutrients, diminution of the digestive process or metabolic utilization of feed) which exerts effect contrary to optimum nutrition. Being an antinutritional factor is not an intrinsic characteristic of a compound but depends upon the digestive process of the ingesting animal. Trypsin inhibitors, which are antinutritional factors for monogastric animals, do not exert adverse effects in ruminants because they are degraded in the rumen (Cheeke and Shull, 1985). Many plant components have potential to precipitate adverse effects on the productivity of farm livestock. These compounds are present in the foliage and seeds of virtually every plant that is used in practical feeding (D’Mello, 2000).
Nutritional effect of major antinutrients in plant protein sources: The major antinutrients mostly found in plant protein sources are toxic amino acids, saponins, cyanogenic glycosides, tannins, phytic acid, gossypol, oxalates, goitrogens, lectins (phytohaemagglutinins), protease inhibitors, chlorogenic acid and amylase inhibitors.
Toxic amino acids: A wide range of toxic non-protein amino acids occur in the foliage and seeds of plants. These toxic non-protein amino acids appear to play a major role in determining the nutritional value of a number of tropical legumes (D’Mello, 1982). It has been proposed that these amino acids act antagonistically towards certain nutritionally important amino acids (Liener, 1980). Fowden (1971) suggested that the metabolic pathways culminating in the synthesis of certain non-protein amino acids might reflect subtle alteration in the genome responsible for directing the formation of crucial amino acids. Bell (1971) reported that while non-protein amino acids function primarily as storage metabolites, they may also provide an adaptive advantage to the plants, for example to render the plant less susceptible to attack by various animals and lower plants. Some of these toxic amino acids includes; djenkolic acids, mimosine and canavanine. Mimosine, a toxic non-protein amino acid structurally similar to tyrosine, is contained in the legume Leucaena leucocephala (D’Mello and Acamovic 1989; D’Mello, 2000). Mimosine has been proven effective in defleecing sheep and goats (Jacquemet et al.,1990; Luo et al., 2000). Mimosine a pyridoxal antagonist, which inhibits DNA replication and protein synthesis; thus, it may elicit defleecing by arresting cell division in the follicle bulb (Reis, 1979). In monogastric animals, mimosine causes poor growth, alopecia and reproductive problems. Levels of Leucaena meal above 5-10% of the diet for swine, poultry and rabbits generally result in poor animal performance. The major symptoms of toxicity in ruminants are poor growth, loss of hair and wool, lameness, mouth andoesophageal lesions, depressed serum thyroxine level and goitre. Some of these symptoms may be due to mimosine and others to 3, 4-dihydroxypyridine, a metabolite of mimosine in the rumen (Jones and Hegarty, 1984). Djenkol beans (Pithecolobium lubatum) when ingested sometimes lead to kidney failure which is accompanied by the appearance of blood and white needle-like clusters in the urine. The clusters are sulphur-containing amino acids known as djenkolic acids which are present in the bean in the free state, to the extent of 1-4%. This toxic amino acid is structurally similar to cystine, but it is not degraded in the animal body. Due to its insolubility it crystallizes out in the kidney tubules and escapes through urine (Enwere, 1998). The toxic, non-protein amino acid, canavanine, occurs widely in unbound form in various legume plants of the sub-family Papillonoideae (Bell et al., 1978) and abundantly in jack bean (Canavalia ensiformis (L). DC), constituting up to 63 g/kg dry weight of the seed (Ho and Shen, 1966). Canavanine, a structural analogue of arginine, was first isolated from jackbean by Kitagawa and Tomiyama (1929). Canavanine is believed to exert its toxic influence by virtue of its structural similarity with the nutritionally indispensable amino acid, arginine. Canavanine may antagonize arginine and interfere with Ribonucleic Acid (RNA) metabolism (Rosenthal, 1982). Canavanine has been demonstrated to reduce feed intake of non-ruminants but this was observed only at the equivalent of about 300 g/kg dietary level of raw jackbean Tschiersch, 1962). Saponins: Saponins are a heterogeneous group of naturally occurring foam-producing triterpene or steroidal glycosides that occur in a wide range of plants, including pulses and oil seeds such as kidney bean, chickpea, soybean, groundnut, lupin and sunflower Liener, 1980; Price et al., 1987; Jenkins and Atwal, 1994). It has been reported that saponins can affect animal performance and metabolism in a number of ways as follows: erythrocyte haemolysis, reduction of blood and liver cholesterol, depression of growth rate, bloat (ruminants), inhibition of smooth muscle activity, enzyme inhibition and reduction in nutrient absorption Cheeke, 1971). Saponins have also been reported to alter cell wall permeability and therefore produce some toxic effects when ingested (Belmar et al., 1999). Saponins have been shown to bind to the cells of the small intestine thereby affecting the absorption of nutrients across the intestinal wall (Johnson et al., 1986). The effect of saponins on chicks have been reported to reduce growth, feed efficiency and interfere with the absorption of dietary lipids, cholesterol, bile acids and vitamins A and E (Jenkins and Atwal, 1994).
Cyanogenic glycosides: Some legumes like linseed, lima bean, kidney bean and the red gram contain cyanogenic glycosides from which Hydrogen Cyanide (HCN) may be released by hydrolysis. Some cultivars Phaseolus lunatus (lima bean) contain a cyanogenic glycoside called phaseolutanin from which HCN liberated due to enzyme action, especially when tissues are broken down by grinding or chewing or under damp conditions (Purseglove, 1991). Hydrolysis occurs rapidly when the ground meal is cooked in water and most the liberated HCN is lost by volatilization. HCN is very toxic at low concentration to animals. HCN can cause dysfunction of the central nervous system, respiratory failure and cardiac arrest (D’Mello, 2000).
Tannins: Tannins are water soluble phenolic compounds with a molecular weight greater than 500 daltons. They have the ability to precipitate proteins from aqueous solution. There are two different groups tannins:- hydrolyzable tannins and condensed tannins. Condensed tannins are widely distributed leguminous forages and seeds. Cattle and sheep sensitive to condensed tannins, while goats are more resistant (Kumar, 1983; Kumar and Horigome, 1986; Kumar and Vaithiyanathan, 1990; D’Mello, 2000).Tannins may form a less digestive complex with dietary proteins and may bind and inhibit the endogenous protein, such as digestive enzymes (Kumar and Singh, 1984). Tannin-protein complexes involve both hydrogenruminants bonding and hydrophobic interactions. The precipitation of the protein-tannin complex depends upon pH, ionic strength and molecular size of tannins. Both the protein the precipitate increase with increase in molecular size of tannins (Kumar and Horigome, 1986). However, when the molecular weight exceeds 5,000 daltons, the tannins become insoluble and lose their protein precipitating capacity and degree of polymerization becomes imperative to assess the role of tannins in ruminant nutrition (Kumar, 1983; Lowry, 1990). Tannins have been found to interfere with digestion by displaying anti-trypsin and anti-amylase activity. Helsper et al. (1993) reported that condensed tannins were responsible for the testabloat bound trypsin inhibitor activity of faba beans. Tannins also have the ability to complex with vitamin B (Liener, 1980). Other adverse nutritional effects of tannins have been reported to include intestinal damage, interference with iron absorption and the possibility of tannins producing a carcinogenic effect (Butler, 1989).
Phytic acid: Phytic acid occurs naturally throughout the plant kingdom and is present in considerable quantities within many of the major legumes and oilseeds. This includes soybean, rapeseed and cotton seed. Matyka et al. (1993) reported that about 62-73% and 46-73% of the total phosphorus within cereal grains and legume seeds being in form of organically bound phytin phosphorus, respectively. As phytic acid accumulates in storage sites in seeds, other minerals apparently chelates to it forming the complex salt phytate (Erdman, 1979). Studies by Martinez (1977) revealed that in oilseeds, which contain little or no endosperm, the phytates are distributed throughout the kernel found within subcellular inclusions called aleurone grains or protein bodies. Whole soybeans have been reported to contain 1-2% phytic acids (Weingartner, 1987; Osho, 1993). The major part of the phosphorus contained within phytic acid are largely unavailable to animals due to the absence of the enzyme phytase within the digestive tract of monogastric animals. Nwokolo and Bragg (1977) reported that in the chicken there is a significant inverse relationship between phytic acid and the availability of calcium, magnesium, phosphorus and zinc in feedstuffs such as rapeseed, palm kernel seed, cotton seed and soybean meals. Phytic acid acts as a strong chelator, forming protein and mineral-phytic acid complexes; the net result being reduced protein and mineral bioavailability (Erdman, 1979; Spinelli et al., 1983; Khare, 2000). Phytic acid is reported to chelate metal ions such as calcium, magnesium, zinc, copper, iron and molybdenum to form insoluble complexes that are not readily absorbed from gastrointestinal tract. Phytic acid also inhibits the action of gastrointestinal tyrosinase, trypsin, pepsin, lipase and “-amylase (Liener, 1980; Hendricks and Bailey, 1989; Khare, 2000). Erdman (1979) stated that the greatest effect of phytic acid on human nutrition is its reduction of zinc bioavailability.
Gossypol: Gossypol is a naturally occurring polyphenolic compound present in the pigment glands of cotton seed (Gossypium spp). The average gossypol content varying from 0.4-2.4% within glanded cotton seeds to less than 0.01% free gossypol within some low-gossypol cotton seed meals (Liener, 1980; Robinson and Brent, 1989; Castaldo, 1995). Reduced lysine availability has been reported with cotton seed protein due to the ability of heatgossypol to bind with the reactive epsilon amino group of lysine during heat processing (Wilson et al., 1981; Robinson, 1991; Church, 1991). The general symptoms of gossypol toxicity are depressed appetite, loss of weight, laboured breathing and cardiac irregularity. Death is usually associated with reduced oxygen carrying capacity of the blood, haemolytic effects on erythrocytes and circulatory failure. Dietary gossypol also causes olive-green discolouration of yolks in eggs (Church, 1991; Olomu, 1995; McDonald et al., 1995).
Oxalates: Oxalates affects calcium and magnesium metabolism and react with proteins to form complexes which have an inhibitory effect in peptic digestion. Ruminants, however unlike monogastric animals can ingest considerable amounts of high-oxalate plants without adverse effects, due principally to microbial decomposition in the rumen (Oke, 1969). The hulls of sesame seeds contain oxalates and it is essential that meals should be completely decorticated in order to avoid toxicities (McDonald et al., 1995). Chemical analysis carried by Alabi et al. (2005) on locust bean seeds revealed that the testa of locust bean seeds had the highest concentration of oxalate (4.96 mg/100 g) followed by the pulp (3.40 mg/100 g) and the cotyledon (1.15 mg/100 g). Olomu (1995) reported that pigeon pea contains about 0.38% oxalic acid. Oxalic acid binds calcium and forms calcium oxalate which is insoluble. Calcium oxalate adversely affects the absorption and utilization of calcium in the animal body (Olomu, 1995).
Goitrogens: Goitrogenic substances, which cause enlargement of the thyroid gland, have been found in legumes such as soybean and groundnut. They have been reported to inhibit the synthesis and secretion of the thyroid hormones. Since thyroid hormones play an important part in the control of body metabolism their deficiency results in reduced growth and reproductive performance (Olomu, 1995). Goitrogenic effect have been effectively counteracted by iodine supplementation rather heat treatment (Liener, 1975).
Lectins (phytohaemagglutinins): Phytohaemagglutinins or lectins are glycoproteins widely distributed in legumes and some certain oil seeds (including soybean) which possess an affinity for specific sugar molecules and are characterized by their ability to combine with carbohydrate membrane receptors (Pusztai, 1989). Lectins have the capability to directly bind to the intestinal muscosa (Almeida et al., 1991; Santiago et al., 1993), interacting with the enterocytes and interfering with the absorption and transportation of nutrients (particularly carbohydrates) during digestion (Santiago et al., 1993) and causing epithelial lesions within the intestine (Oliveira et al., 1989). Although lectins are usually reported as being heat labile, their stability varies between plant species, many lectins being resistant to inactivation by dry heat and requiring the presence of moisture for more complete destruction (Ayyagari et al., 1989; Poel et al., 1990; Almeida et al., 1991).
Protease inhibitors: Protease inhibitors are widely distributed within the plant kingdom, including the seeds of most cultivated legumes. Protease inhibitors have the ability to inhibit the activity of proteolytic enzymes within the gastrointestinal tract of animals (Liener and Kakade, 1980). Trypsin inhibitor and chymotrypsin inhibitor are protease inhibitors occurring in raw legume seeds. Protease inhibitors are the most commonly encountered class of antinutritional factors of plant origin. These inhibitors have been reported to be partly responsible for the growth-retarding property of raw legumes. The retardation has been attributed to inhibition of protein digestion but there is evidence that pancreatic hyper- activity, resulting in increased production of trypsin and chymotrypsin with consequent loss of cystine and methionine is also involved (McDonald et al., 1995). Trypsin inhibitors have been implicated in reducing protein digestibility and in pancreatic hypertrophy (Liener, 1976). Trypsin inhibitors are polypeptides that form well characterized stable complexes with trypsin on a one-to-one molar ratio, obstructing the enzymatic action (Carlini and Udedibie, 1997). Protease inhibitors are inactivated by heat especially moist heat, because of even distribution of heat (Bressani and Sosa, 1990; Liener, 1995).
Chlorogenic acid: Sunflower meal contains high levels of chlorogenic acid, a tannin like compound that inhibits activity of digestive enzymes including trypsin, chymotrypsin, amylase and lipase (Cheeke and Shull, 1985). Because chlorogenic acid is uncondensed and non-hydrolyzable, its content of 1% or more of a total of 3-3.5% phenolic compounds in sunflower meal is not reported in tannin assays. Chlorogenic acid is also a precursor of ortho-quinones that occur through the action of the plant enzyme polyphenol oxidase. These compounds then react with the polymerize lysine during processing or in the gut. Although the toxic effects of chlorogenic acid can be counteracted by dietary supplementation with methyl donors such as choline and methionine. Chlorogenic acid is reported to be readily removed from sunflower seeds using aqueous extraction methods (Dominguez et al., 1993).
Amylase inhibitors: Amylase inhibitors are also known as starch blockers because they contain substances that prevent dietary starches from being absorbed by the body. Starches are complex carbohydrates that cannot be absorbed unless they are first broken down by the digestive enzyme amylase and other secondary enzymes (Marshall and Lauda, 1975; Choudhury et al., 1996). Pigeon pea have been reported to contain amylase inhibitors. These inhibitors have been found to be active over a pH range of 4.5-9.5 and are heat labile. Amylase inhibitors inhibit bovine pancreatic amylase but fail to inhibit bacterial, fungal and endogenous amylase. Pigeon pea amylase inhibitors are synthesized during late seed development and also degraded during late germination (Giri and Kachole, 1998).
Conclusion: The presence of antinutrients in plant protein sources for livestock feeding is a major constraint that reduces their full utilization. To be able to justify the overall nutritional potential or value of any plant protein source, proper assessment of the type, nature and concentration of the antinutrients present in the protein source and also the bioavailability of nutrients to the ingesting animal is necessary. Employing appropriate and effective processing techniques or combination of techniques could help reduce or eliminate the adverse effects of these antinutritive constituents in plant protein sources and thereby improve their nutritive value. Supplementation of some minerals, animo acids and vitamins could help reduce or neutralize the negative effect of antinutritional factors in plant protein sources for livestock nutrition. The concentration or level of the antinutritive constituents in these protein sources vary with the species of plant, cultivar and post-harvest treatments (processing methods). Since antinutrients vary among plant cultivars, therefore the use of genetically improved low-antinutritive livestock feeding. cultivars or varieties could be a possible option for livestock feeding.