Download Lecture No. 8

FOOD TOXINS 2
Lecture No. 8
Copyright © Mgr. Zuzana Široká, PhD.
PROTEASE INHIBITORS
• Occurrence: mainly in legumes, but also in potatoes, cereals etc.
• These inhibitors exist in food of animal origin too
• Serve as a protection of cytosole against undesirable proteolysis in damaged
tissues and against predators
• They are also storage proteins for the time of germination
• Two main types exist:
1) Bowman-Birk type:
- two binding places, block trypsin,chymotrypsin and other proteases
- in many foodstuffs: legumes, potatoes, soya, tomatoes, maize and other
cereals, tea, coffee, cheese, fish, meat etc.
2) Kunitz-type
- one binding place, block usually trypsin or chymotrypsin
- in soya beans
• They decrease growth, cause pancreas hypertrophy, depletion of digestive
enzymes
with their new synthesis the organism loses essential aminoacids
from liver
• They can be destroyed or inactivated by heat
SUBSTANCES BINDING MINERALS
Phytic acid and phytates:
• They are storage form of phosphorus in a plant
• They are necessary for germination
• Phytic acid is a chelating agent, forms complexes
with Fe, Cu and Zn, and can bind enzymes too (e.g.
pepsin) – blocks absorption of these important
minerals and causes starch to be less digestible –
worse nutrition
• In every plant, but highest concentrations in cereals,
legumes, nuts and spices
• They are heat-stable
• On the other hand, they protect against cancer, one of
the breakdown products is inositol triphosphate,
which enhances natural killer cells activity
Oxalates:
• Bind Ca, make salts with it. These salts cumulate in
kidneys and can cause kidney stones
• Can cause a lack of calcium in an organism which leads
to disturbance of metabolism of bones
Glucosinolates:
• Occur in Brassicaceae, Resedaceae and Capparaceae
families mainly
• Vegetables as cabbage, turnips, radish, mustard seed
contain them in high concentration
• They are synthesized from aminoacids and contain
sulphur in their molecule
• General formula:
S --- glucose
R
C
N
O
SO-3
-
• Glucosinolates are destroyed by enzymatic
hydrolysis due to enzyme called myrosinase
• In normal conditions, thiocyanates and
isothiocyanates are formed; under pH 4, nitriles and
elementary sulphur are established
• Glucosinolates are heat-unstable, so they are partially
destroyed by cooking
• Some most important of them : erucin, glucobrassicin,
glucosinalbin, glucoerucin, sinigrin, progoitrin
• They are of acrid taste and these characteristics are necessary in
mustard and horseradish, but not in other species
• Goitrin, a breakdown product of glucosinolates, interferes with
iodine uptake in to thyroid gland (blocks it), it is so called
strumigen
• Increased intake of glucosinolates leads to increased activity of
thyroid gland, which has to catch iodine more carefully, cells of
its epithelium grow and hypertrophy follows – struma is formed.
Adding iodine to food doesn’t have a detectable effect on this
process, once the gland is increased
• Goitrin can also affect liver, kidneys and adrenal glands
• On the other hand, some of the breakdown products, especially
3-hydroxymethylindol and ascorbigen, activate enzymes in gut
and liver so the detoxification of xenogenic compounds is
quicker, have an anti-cancer effect
PHYTOESTROGENS
• These are compounds, which in an animal body
mimic the effect of estrogens
• They are of non-steroidal character, usually they are
isoflavones (genistein, daidzein, formonetin)
• They are found in soya, apples, carrot, cereals,
potatoes, peanuts, olives, clover, alfa-alfa etc.
• Naturally they act as contraceptive agents – cause
hypertrophy of uterus, mammary glands, disturb
hormonal cycle etc. All these effects are usually
temporary and disappear after some time when the
diet is changed
• They are used as a treatment in menopausal women.
• Phytoestrogens have lower affinity and activity in
estradiol receptor than estradiol itself. If the
concentration of natural estradiol in blood is low, their
effect is additive. They help to occupy receptors and
activate them
• In young women they act as antagonists, because they
don’t allow to certain amount of estrogens in blood to
bind to receptors and don’t activate them as much as
estradiol – the protection of hormone-sensitive tissues
against cancer
• But this is only in small amounts, in higher, they disturb
all these processes and are more harmful than useful –
warning for vegetarians. Excessive intake in men can also
cause problems with reproduction
For example:
45 mg of isoflavones can disturb hormonal cycle in healthy women:
(Daily intake)
(μg/g Wet Wt)
Daidzein
Genistein
Tofu
Soya sauce
Soya milk
Soya beans-cooked
Fresh soya beans
Soya burger
76
8
18
138
546
49
166
5
26
230
729
139
If you eat a tofu for your lunch, which weighs 100 g, your intake is 7600 μg of daidzein and
16 000 μg of genistein, which is 23,6 mg of isoflavones per one lunch.
TOXIC AMINOACIDS AND
PROTEINS
Haemolytic aminoacids:
• They are free aminoacids in Brassicaceae family plants
• It is S-methylcysteinsulfoxide (SMCO) and its precursor Smethylcystein (necessary for cystein and methionin synthesis)
• High concentration of SMCO is in young tissues and represents
a storage reservoir of sulphur in an organism. Its production is
stimulated by adding fertilizers to soil
• Bacterial microflora in gut forms dimethyldisulfide form SMCO
• This needs glutathione to reduce. But glutathione is important
especially for red blood cells and their membrane
• If there is a lack of glutathione in an excessive intake of SMCO,
methaemoglobin is formed in unprotected red blood cells. It
settles on the surface of red blood cells forming so called HeinzEhrlich corpuscles which in higher concentration damage the
membrane and cause haemolysis. It causes haemolytic anaemia
Lathyrogens:
• In Fabaceae family
• Vicia sativa, Lathyrus sativus and odoratus – vetch and
sweet pea
• Toxic are free aminocids – oxalylamino-alanin, cyanoalanin and diaminobutyric acid
• In Northern Africa, form vetch and sweet pea flour is
made, when there is not enough other cereals
• The intoxication is called neurolathyrism and signs are
paresis and paralysis of legs, and other type is
osteolathyrism, for which a disturbance of collagen and
elastin metabolism is typical
• The effect of toxic lathyrogens is possible due to their
high similarity to common aminoacids, so they are
involved in their metabolism, which they disturb