plant toxins - food toxicology

1. ENDOGENOUS PLANT
TOXICANTS
D.MEGHANA NAIDU
MSc. FOOD TECHNOLOGY

2. “
”
Toxic components can reach our
table, for eg. Via the milk or
meat of the animals that have fed
toxic plants, or honey,
contaminated with environmental
toxicants
Here are some of the most important plant – borne toxicants
from various parts of the world…!

3. LECTINS or HEMAGGLUTININS
 LECTINS are NON ENZYMATIC – THERMOLABILE PROTEINS,
glycoproteins or lipoproteins that selectively bind to saccharide
(glucose, galactose, etc) groups.
 These are found in more than 800 edible plants…!
 Since many but not all, Lectins are capable of agglutinating
erythrocytes and other cells, they are often called HEMAGGLUTININS.
 SOURCES : Leguminous plants viz., various beans & peas (pulses).
*lectins have also been found in animals viz., sponges, molluscs,
fish(in blood), amphibians(in the eggs)& mammals including human
tissues…!
 USES : In practice lectins are used for blood group typing, recognition
of tumor cells, for the investigation of signal transmission,
mitogenesis and cell death.
 ADVERSE EFFECTS : A long term consumption of raw legumes may lead
to growth retardation and even goiter. Acute systemic exposure -
fatal injury of liver and other organs.

4. • Some lectins, especially ricin from the seeds of the castor oil plant and abrin from
jequirity bean or rosary pea , are serious poisons.
• A ricin molecule consists of two polypeptide subunits (short A and long B chains),
linked together with S–S bridges.
• In case of being ingested, ricin causes a severe necrosis of intestinal wall cells, and
death via a multi-organ damage.
• Yet, the absorption of ricin from the intestines is rather small and percutaneous
absorption is negligible.
• Inhalation and injections are much more dangerous routes of ricin administration.
• Ricin produces, for example, hepatotoxicity, nephrotoxicity, and oxidative damage at
24 h of post intraperitoneal (i.p.) treatment of rats.
• Hepatotoxicity is the most prominent type of ricin toxicity (Kumar et al., 2003).
• The LD50 of ricin to humans is 5–10 µg/kg or 350–700 µg for an adult weighing 70 kg
in case of inhalation of solid particles or intravenous or intramuscular injection.
• The toxicity of ricin is extremely high—one molecule of ricin is capable of killing
one cell.
Lectins cont… example

5. ENZYME INHIBITORS
 Extremely proteolysis resistant proteins are found in all plants. But in
large quantities in SOYBEAN (the kunitz inhibitor) other beans, peas,
beet, cereals (corn,wheat,rye,rice) , clover & potato.
 These are mostly inhibitors of a serine protease trypsin.
 But the inhibitors of chymotrypsin and carboxypeptidase B have also
been found in plants.
 ADVERSE EFFECTS: Long term eating (raw source) of even small
amounts of various protease inhibitors can increase the risk of
1. growth retardation
2. Cancer
3. Pancreatic hypertrophy – on the binding of inhibitor molecule to the
enzyme molecule, the pancreas receives a signal for the synthesis of a
new enzyme molecules, which may finally lead to the hypertrophy of
the exocrine pancreatic tissue.

6. Enzyme inhibitors cont…
 Thermal processing usually denatures the proteinaceous inhibitor
molecules. For eg., in case of potatoes, microwaving & boiling are
more effective than cooking.
 Since, many vegetables are eaten without any processing or after a
short term cooking, they can still exert at least a partial inhibition
capability of the digestive enzymes.

7. ALKALOIDS (Arabic word- “al-qali”)
meaning both alkali & alkaline properties
 ALKALOIDS are nitrogen containing heterocyclic compounds that exert
a pharmacological effect in humans and animals.
 In plants, alkaloids are defenders against herbivorous animals,
parasites and insects.
 Alkaloids also found in fungi and in animals.
 Alkaloids due to their alkaline properties, form water soluble salts
with acids.
 A number of plant alkaloids ae toxic for animals (some of them have a
bitter taste).
 Alkaloids viz., morphine or codeine, are used in medicine as
analgetics.
 Humans may have contact via food mostly with pyrrolizidine, xanthine
& solanine alkaloids.

8. 1.Pyrrolizidine alkaloid
 Are complex molecules named for their inclusion of a pyrrolizidine
nucleus ( a pair of linked pyrrole rings )
 Cause hepatotoxicity
 Honey contains good amount of pyrrolizidine alkaloid.

9. 2.Xanthine alkaloids
 Xanthine (xanthic acid), is a purine base found in most human body
tissues & fluids & in other organisms.
 A no. of stimulants derived from xanthine, including caffeine and
theobromine.
 CAFFEINE is almost entirely metabolized by liver.
 Normal caffeine drinkers have 0.2-2ug/ml in plasma.
 If it is10-30ug/ml (toxicological effect begins).
 Lethal dose 5g for child & 10g for an adult. (However, recovery has
been recorded even after the ingestion of 30 g caffeine)
 Threshold dose for chronic effect is 500-600mg/day for an adult
human weighing 70 Kgs.

10. Xanthine alkaloids cont…
 Lowest acute dose for adverse effects  5-15mg/kg.
 Acute intoxication with caffeine 1st causes headache, nausea, &
gastrospasm, sleepyness, excitement & palpitation of heart
( sensation that your hearthas skipped a beat or added an extra beat
)……… which starts at the administration of 0.5-1 g of caffeine.

11. 3.Solanine- group alkaloids
 Steroidal alkaloids a–solanine, a- chaconine & tomatine, also belong
to the group of terpenoids (found in potatoes, brinjal-egg plant,
tomatoes, berries of night shade.
 Usual glycoalkaloid content in tubers is 20-100mg/kg.
 In potato chips, summary content of glycoalkaliods is 20-600mg/kg (
has been reported by rietjens et,al, 2005).
 Total daily toxic dose of solanine & chaconine (LOEL) FOR HUMANS IS
2-5 mg/kg ., lethal dose being 3-6 mg/kg. (these two doses are
extremely close to each other)
 Cooking, boiling or microwaving do not destroy the alkaloids, but their
content is reduced by 3 times by peeling….as most of the alkaloids are
located in the surface layer and in the peel, that is why smaller tubers
are relatively toxic.

12. solanine cont..
 The intoxication symptoms (headache, vomiting, diarrhea,
neurological disorders, weakness & even death), part of
which can be related to the irritative and
anticholinesteratic effect
( potentiating the action of acetylcholine, a major neurotr
ansmitter carrying nerve impulses
across synapses and from nerves to muscles.
Continued action causes serious effectslike nausea, vomit
ing, sweating, salivation,restlessness, tightness of the che
st, blurred vision, diarrhoea convulsions and death ) of
alkaloids, appear at the total concentrations of
glycoalcaloids exceeding 200mg.

13. CYANOGENIC GLYCOSIDES (HCN)
 The glycosides of a low toxicity, containing –CN cyanic groups and releasing
highly toxic HCN at their enzymatic hydrolysis, are not only found in plants
(over 300) but also present in mushrooms, bacteria and even in animals.
 The list of respective dietary plants and foodstuffs include cassava, sweet
potato, yam, corn millet, sorgo, sugar cane, peas, almonds, lemons, apples,
pears, cherries, apricots, etc.
 From the 20 cyanogenic glycosides identified so far, the most interesting are
four – amygdalin, dhurrin, linamarin and lotaustralin.
 The hydrolysis of cyanogenic glycosides is promoted by physical destruction as
well as by stress (drying, freezing, cooking ) and is catalyzed by enzymes b-
glucosidase and hydronitrile lyase, which are found both in plants & in the
digestive tract of humans as well as of animals.
 The most well known and widely produced glycoside is amygdalin, which is
present in the bones of the fruits of drupaceous plants.

14. Cyanogenic glycosides cont…
 Amygdalin is an odorless & bitter substance, readily soluble in wather and
ethanol.
 Amygdalin content is different in various fruits ( in bitter almonds 2.5-
3.5%), (in peach seeds 2-3%), (in apricot stones 0.1-4%), ( in plum stones
1-1.8%), (in cherry stones 0.8%). smaller concentrations are also found in
the seeds of apple and pears.
 Amygdalin is not destroyed even during drying, boiling, cooking or stewing
of the stones.
 Human can obtain a lethal dose from 50-60 (bitter almonds) and 100
stones (plum or apricot).
 It has been estimated that the average daily dietary consumption of HCN
is 46-95ug per person.
 The minimum lethal dose of HCN is 0.5-3.5 for humans and 2-10mg/kg for
animals.
 HCN in blood plasma, toxic conc 0.2ug/ml & lethal conc 1ug/ml.

15. PHYTOESTROGENS
 Phytoestrogens are plant compounds which can produce effects like that of
the hormone estrogen when ingested into the body.
 Although their affinity for binding is 20-200 times less than that of estradiol,
they compete with estradiol receptor sites.
 Phytoestrogen content in plants is highest during blossoming.
Phytoestrogens are :
 Various flavonoids ( isoflavones, genistein, glycetein, daidzein, formononetin
& biochain A) their glucosides (genistin, glycetin & daidzin) from soybean,
favabean, kuduz, alfalfa,peanut, etc.
 Coumestans viz coumestrol & 4-O-methylcoumestrol from legumes and clover.
 Stilbeans viz resveratrol from grapes & red grape wine, peanuts & garden
shubarb roots.

16. Phytoestrogens cont…
 Ligands from flax, pumpkin, & sesam seeds, rye, soybeans, broccoli, beans&
some berries.
 Resorcyclic acid lactones viz mycotoxins zearalenone.
 Equol -4’,7- isoflavandiol, an isoflavandiol, biotrasformed from daidzein or
formononetin by the intestinal bacterial flora.

17. SAPONINS
 Saponins are glycosidic saponaceous surface-active substance.
 They are found in soybeans, sugar beet, peanuts, spinach, broccoli, alfalfa,
potato, apples and in other plants and fruits.
 saponins are very toxic substances ; owing to their surfactant activity, they
are able to decompose cellular membranes.
 They can elicit blood hemiolysis, especially in the case of cold-blooded
animals.
 For warm blooded animals , small per orally administered doses of saponins
are generally harmless., since they decomposed by enteric microflora.
 In addition they are poorly absorbed and their effect is inhibited by blood
plasma.
 Nevertheless, in the case of large doses of saponins, nausea, vomiting,
diarrhea and dizziness can occur.

18. OXALATES
 Rhubarb, spinach, parsley, chives, purslane, cassava, amaranth, beet
leaves, taro leaves, radishes, ollards, monstera fruit, tea, and cocoa
contain a large amount of (0.3–2.0% of wet weight) oxalic acid.
 Oxalic acid is a strong acid that irritates tissues. Oxalates form tiny
insoluble crystals with sharp edges, which also irritate tissues.
 Consequently, high levels of oxalic acid/oxalates in the diet may lead to
adverse effects on the digestive system, particularly of the stomach and
kidneys.
 Oxalates may also contribute to the formation of calcium oxalate stones
in the kidneys. As a result of the accumulation of calcium oxalate,
degeneration of kidneys as well as blood vessels and necrosis may occur.
 Oxalic acid is capable of chelating blood calcium resulting in
hypocalcemia, coagulation disorders, and tetany.

19. Oxalate cont..
 Oxalates also influence the absorption of calcium, iron, magnesium,
and copper and inhibit the metabolism of succinate dehydrogenase
and the metabolism of carbohydrates.
 The lethal dose of oxalates is reached on consuming 5 kg of rhubarb,
2.5 kg of tomato, or 0.5 kg of spinach leaves.
 The symptoms of oxalate poisoning are weakness, flushing in the
mouth and throat, respiratory distress, abdominal pain, nausea,
vomiting, diarrhea, convulsions, coma, and death as a result of the
collapse of the coronary heart system. Oxalate intoxication is much
more common in animals. The LD50 (rat) is 375 mg/kg. The toxicity of
oxalic acid

20. Oxalates cont…
 Should we totally avoid vegetables containing oxalic acid such as
spinach, star fruit, or rhubarb?
 Oxalic acid in vegetables is broken down during cooking and does not
interfere with the absorption of the calcium present in other foods,
for instance, cheese that anybody might eat at the same time.
Calcium is available from many other food sources—yogurt, cheese,
cow milk, orange juice, soy milk, and cereals.

21. SOYBEAN AS A POTENTIAL SOURCE OF
VERSATILE POSSIBLE TOXICANTS
 Fruits of soybean are very rich in nutritive components.
 Besides the very high protein content, soybeans contain a lot of fiber
and are rich in calcium and magnesium & a high biological value
containing all the essential amino acids.
 nevertheless, consumers of soy products must be aware about a number
of possible, although not severe, toxic or antinutritive effects caused by
definite chemical constituents of soybean.
 Fresh soybeans contain the following toxic or antidietary constituents :
1. Phytoestrogenic isoflavones viz genistein and daidzein and their
glucosides disrupt the endocrine function and have the potential to
cause infertility and promote breast cancer in adult women. Soy
phytoestrogens are potent antithyroid agents that cause
hypothyroidism(may cause thyroid cancer) auto immune thyroid disease
in infants.

22. Soya Cont…
1. Extremely allergenic proteins. The processing of soya to tofu or soy
milk reduces allerginicity. Soya oil is void of allerginicity.
2. Large amounts of proteinous inhibitors of enzymes, such as the
soybean Kunitz trypsin inhibitor , interferes with protein digestion and
may cause pancreatic disorders up to hypertrophy. In test animals, soy
containing trypsin inhibitors have caused stunted growth.
3. High levels of phytic acid that reduce the assimilation of calcium,
magnesium, copper, iron, and zinc. Phytic acid is not neutralized by
conventional preparation methods such as soaking, sprouting, and
long, slow cooking. High-phytate diets have caused growth problems
in children.
4. High levels of aluminum, which is toxic to the nervous system and the
kidneys.

23. Soya Cont…
 In addition, toxic lysinoalanine (metal chelator in proteins) and carcinogenic
nitrosoamines are formed during the processing of soya protein.
 Soy foods must be exhaustively cooked or fermented to neutralize multiple
natural toxicants.
 During processing, most of the toxic and antidietary constituents of soybean
are destroyed by the bacteria or heat.
 Natto, a popular soy product in Japan, is healthy due to the high content of
vitamin K2 and is anticarcinogenic and possesses antimicrobial activity.

24. MUSHROOM TOXINS
General principles
Eating mushrooms may be connected with various hazards:
1. Real mushroom poisoning:
a) With persistently toxic mushrooms. Many mushrooms lose their
toxicity during processing.
b) With old mushrooms. Toxic substances are formed during the
decomposition of the mushrooms.
2. Poisonings by environmental toxicants, bioaccumulated in mushrooms.
3. Allergic-supersensibility reactions against mushroom constituents

25. Mushroom Cont…
 Two mushrooms of the genus Amanita—the green death cap (A.
phalloides) and the white death cap (A. virosa)—are really fatally
toxic, which contain amatoxins (α-, β-, and γ-amanitins) and
phallotoxins such as phalloidin, phalloin, phallacidin, and phallolysin.
In addition, A. virosa contains virotoxins.
 Amatoxins are thermostable and insoluble in water; they cannot be
destroyed either by boiling or by cooking as well as by drying of the
mushrooms.
 Phallotoxins induce severe gastroenteritis, appearing 4–8 h after the
ingestion of the white death cap; but, owing to negligible absorptivity,
this group of toxins has no essential role in mushroom poisonings.

26. Mushroom Cont…
 Amatoxins or amanitins are divided into five subtypes—α and β subtypes
being the most important ones.
 Amatoxins are cyclic octapeptides (MW ≈ 900) that after absorption via
amatoxin-transporting system block the synthesis of mRnA in the
eukaryotic cells by the inhibition of the enzyme RnA polymerase II. This
inhibition causes a continuous fall of the mRnA concentration and rate of
protein synthesis in the cell and the cell death during the first 24 h after
the ingestion of the mushroom. These processes take place first in the
digestive tract, and thereafter in the liver and kidneys.
 Liver necrosis (the most critical injury) and decomposition of the renal
tubular cells may also occur.
 Thionic acid is used for curing the amatoxin-caused intoxication.
 The toxin of Amanita pantherina damages the nervous system.

27. Thank you
reference ….. Principles of food toxicology…..