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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