It is generally known that trace elements (microelements) play an important role in living organisms, their research is becoming more widespread. These days it’s already been proven that practically there is no enzyme that would not be in any connection with the major part of the microelements. The product development workgroup of Bio-Fungi Kft. based in Áporka is working on the cultivation technology of a new mushroom product family. During the research, they add inorganic and organic selenium compounds at different points of the cultivation technology that button mushroom can absorb while growing and install in its body. We have investigated how selenium added to the soil of cultivated button mushroom enters the mushroom and how we could increase the selenium content of our body by eating this mushroom.
Hungary has selenium deficiency so for people living here those foods are very important which can replace the missing selenium in the body: eg.: Seleno bread or margarineenriched with selenium. Also, mushroom may be suitable to replace the selenium needs of the body if it can accumulate selenium in its body.
White button mushroom (Agaricus bisporus) is cultivated in the biggest volume in the world – 4 million tons/year of which in Hungary is grown 25,000 tons/year. Since besides its low carbohydrate content it is a significant source of protein and its mineral salts and trace elements content is high, it is an important food from the point of view of healthy eating. One third of the amino acid amount of of button mushroom is the essential amino acids and the sulfur-containing amino acids and aromatic acids are relatively in small quantities. Button mushroom is rich in potassium and phosphorus but it also contains other minerals in large quantities. The selenium content of cultivated button mushroom is 1-4 mg/kg. Our goal was to increase that quantity by treating growing surface with different selenium compounds.
The relation between selenium and tumor protection, the physiological role of selenium
In the human body selenium can be found in a concentration of only about 0.2 mg/kg, meanwhile in the adult body the total amount is only about 10-15 mg (1) of which the majority occurs in the soft tissues. Selenium basically plays a role as an antioxidant and is mostly involved with Tocopherol in the metabolism of the body. The enzyme glutathione peroxidase contains selenium and catalyzes the reaction of peroxid depleting. Thus, it protects the membranes from oxidative destruction protecting the safety of the unsaturated lipids and cell membranes.
Selenium in the body is absorbed from the intestinal canal, the ileum and the duodenum with good efficiency. The efficiency of absorption is usually 50-70% but approximate 100% absorption was also measured. In case of rich protein supply the absorption of selenium increases in while in case of protein deficiency it drops. The absorbed selenium is leaving mainly with the urine. A selenium concentration of an average of 77 mcg / l (SD 32 ug / l) was measured in Hungary in human blood plasma . Numerous selenium compounds are known which contain selenium in inorganic (eg. selenite, selenate) and organic (eg.in food of animal origin selenocysteine, selenomethionine in food of plant origin) compounds. The Methil-selenocysteine and the selenocysteine prevent cancer and have antioxidant effect in the protection of cells against oxidative stress. It is therefore necessary to examine the different compound forms of selenium besides the total selenium (2).
The need for selenium can not be clearly defined. In the US, as an RDA value of 0.05-0.07 mg is accepted while for the good supply a daily selenium importation of 0.10-0.15 mg is needed. In the case of selenium, similar to some other microelements, but differently from the most microelements, the tolerance range between the biological needs and poisoning limits is pretty tight.
Selenium is one of microelements which have the smallest tolerance range. Nowadays, we consider a daily intake of 0.20 mg as the limit of toxicity so in case of higher daily intake than this you have to count with poisoning symptoms (selenium poisoning) as hair and body hair loss, skin lesions, garlic smell breath, disorders of the central nervous system and tooth damage. The rich selenium intake (an amount that exceeds the biological demand only slightly) has anti-cancer effect but intake in larger quantities (in quantities of poisoning limit or exceed this) facilitate the development of tumors.
Selenium and tumors
At first place selenium is in the body as compound of protein complexes involved in the endogenous antioxidant processes. That’s why it is useful in the prevention of tumors and reduction of side effects of radiotherapy and chemotherapy. The latter is indicated especially in the positive effect on lymphatic edema emerged after surgery or radiotherapy (3).
Micke (3) has found that in case of tumor diseases selenium levels in the blood is already low 1-5 years before clinical diagnosis. Many studies have confirmed the lack of selenium in case of various tumor diseases. The relationship can be probably explained by the decreased antioxidant capacity of the body because it’s long been known that the stress caused by free oxygen radicals is an important component in the development of cancer. Numerous studies have confirmed the role of selenium in the prevention of tumor diseases from which the most known is the Clark-study realized between 1983-1996 (4) and currently several comprehensive studies are in process.
Moreover the combined radiation and chemotherapy used in the curative or palliative treatment of cancer diseases increases the charging of free radicals of the body. In the last decade the protective effect on healthy cells of selenium was confirmed. At the same time several tumor cells can not include glutation connected with selenium which weakens strongly the protective mechanisms of the cells. The effect against edema of selenium also seems to be clearly confirmed which can be used easily and effectively in case of edema of lymphatic congestion occured during the treatment of in the treatment of tumors of head, neck and chest.
Deficiency of selenium in the human body
Although the biochemical or biological role of selenium is not explored in any way, the fact is that data on its toxic effects are available for a very long time. From zoological and human biological perspective there are selenium poor areas not only in China but also in numerous other countries around the world (eg. Scandinavian countries). Because of selenium deficiency, numerous health problems can occur, the incidence of certain diseases can significantly increase and unfavorable changes can be occured in the human body. The main symptoms are as follows (5):
- anemia, sickle cell anemia,
- increased incidence of Alzheimer’s disease,
- Lesions, moles, birthmarks,
- Eye cataract,
- tumor formation, increased sensitivity to carcinogenic substances,
- cardiomyopathies, cardiac dysfunction, irregular pulse beat,
- increased infant and child mortality, sudden infant death, low birth weight,
- retarded growth,
- immune system problems, increased susceptibility to HIV infection,
- infertility, sterility in men,
- muscle wasting, muscle aches,
- liver cirrhosis, pancreatitis, pancreatic atrophy and degeneration,
- Parkinson’s disease.
In case of selenium, the synergism with Vitamin E is well known but its antagonistic elements in the first place are sulfur, arsenic and silver.
Selenium content of foods
For plants selenium is not an essential element, so they have no symptoms of deficiency. Depending on the amount of selenium absorbed from the soil, there are quite big differences in their selenium concentration (6). On acidic and neutral soil, selenium are usually poorly absorbed but from soil with good ventilation, under aerobic conditions and in an alkaline environment, selenates can be well absorbed.
Certain plants that accumulate selenium can even content in a g/kg amount this element but most plants are capable to absorb selenium only in mg/kg on a soil with a high selenium content. On soil of small selenium, eg. the selenium concentration of plants produced in Scandinavia are very low, usually less than 0.1 mg/kg.
The selenium content is interesting only from the perspective of phytotoxicity in connection with plants or plant foods (the garlic smell of the plants consider to a high selenium content), the very low selenium content causes zoological and human biological problems. Toxic selenium concentration for plants is higher than in case of animals and humans. Such areas do not exist in Central Europe but in regions of Australia, North America and some parts of Ireland the selenosis often.
In the Scandinavian countries, it is considered very important that the residents take the appropriate amount of selenium from food. This may on the one hand by selenium-containing fertilizers, while on the other hand can be achieved by selenium added forage in animal feeding (they have not only solved the needs of selenium of livestock but also the optimum selenium concentration of products of animal origin). Of course there are other possibilities in Hungary as well to supply the population with selenium. These functional foods can be considered as selenium rich or selenium-enriched food such as eg. button mushroom grown on selenium enriched soil, selenium enriched yeast, special baked goods, sales of Brazilian nuts of natural origin with high selenium content or regular apply of complex nutriotion supplements of microelements containing selenium (7).
Among the foods that are generally rich in selenium those which are high in protein therefore, fruits and vegetables usually contain little or very little selenium.
Foods rich in selenium
Because of the chemical similarity between sulfur and selenium, in foods with high protein content (also rich in sulfur amino acids) there are more selenium than in foods of high carbohydrates content. That is why the selenium content is higher in leguminous plants with high protein content (1-10 ug/100 g) than in vegetables. However, it is also true – also reiterating that selenium has no essential character of plants – that legumes grown on selenium-rich soil may contain more selenium as those one grown on selenium-poor land. In Hungary there is information on the selenium content of certain foods (8): vegetables contain mostly 1 ug/100 g, the legumes 3-10 ug/100 g.
In our diet, meat, eggs, fish and cereals are the main sources of selenium (9). The average selenium content of meat, fish and eggs is 10-50 ug/100 g and egg yolk has a higher selenium content than glair (10). At the same time it must be emphasized that selenium is an essential element for animal organisms and its distribution in body tissues of healthy animal because of properly controlled processes, certain foods of animal origin contain relatively little selenium. Nevertheless, if somebody consume well-balanced foods containing animal proteins in big quantities has little chance of a selenium deficiency.
Hungary can not be considered well furnished with selenium from soil and land geographical point of view but also can not be counted among the very selenium-poor areas. In this way, the traditional diet mostly covers the biological needs or comes close to it without selenium supplement. We would like to emphasize that the literature regardint selenium is very rich and a significant portion (about one third) of the publications of the last fifty years of microelements has dealt with selenium (7).
Selenium-enriching in button mushroom
We have experiences that basic treatments with selenium salt both in the case of inorganic water solution and in the case of selenium salt added to selenium yeast solution influence the selenium content of mushrooms. With the selenium solution with yeast, we achieved larger (almost one and a half times higher) selenium enrichment than with the water solution. But on fertile ground with a selenium content of 500 mg/kg there wre no fruiting body because of the big hydrogen selenide (SeH2) formation. The selenium content of the control mushroom which was grown on soil no-treated with selenium salt was 1 mg/kg calculated on dry matter. Regarding fresh button mushroom, this means a value of 0.1 mg/kg because the raw mushroom contains an average of 90% of water so in 1 kg of fresh mushrooms there is 100 ug of selenium. In this way, 20 micrograms of selenium is intaken to our body by consuming one (relativly large) portion, 200 grams of raw mushroom. It would be recommendable to intake ten times more selenium with the same amount of mushroom to our body so it could improve the selenium supply of our body and it is still below the toxic amount. This can be achieved by setting the selenium concentration to a value of 10 mg/kg thus 200 g of the same mushrooms will contain about 200 micrograms of selenium. To achieve this, the breeding ground of the mushroom must be treated with a 10 mg/kg of selenium saline. By eating the food prepared from that assumed 200 grams of button mushroom 200 micrograms of selenium is possible to intake which means only the lower value of the upper limit of the daily need. So the toxic level can not be reached even with selenium intake of other food.
Name and contact of the beneficiary: Bio-Fungi Kft, 2338 Áporka, Szabadság telep 030/10.
Participating organizations: MAG Zrt.- 1139 Budapest, Váci út 83. www.magzrt.hu; National Development Agency – 1077 Budapest, Wesselényi u. 20-22. www.nfu.hu