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Determination of the Silicon Content in Dietary Supplements and in Water*

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Determination of the Silicon Content in Dietary Supplements and in Water* Journal of Elementology ISSN 1644-2296 Putko P., Kwaśny M. 2019. Determination of the silicon content in dietary supplements and in water. J. Elem., 24(3): 1143-1158. DOI: 10.5601/jelem.2018.23.4.1766 RECEIVED: 14 November 2018 ACCEPTED: 30 April 2019 ORIGINAL PAPER DETERMINATION OF THE SILICON CONTENT IN DIETARY SUPPLEMENTS AND IN WATER* Paulina Putko1, Mirosław Kwaśny2 1 Biomedical Engineering Center, Institute of Optoelectronics 2 Institute of Optoelectronics Military University of Technology in Warsaw, Poland ABSTRACT Silicon (Si) is one of the most important elements on the Earth, and an essential element for all living organisms. In the last two decades, the benefits of silicon in plants, animals and humans have been proven. The content of this element in the human body is from 6 to 7 g, almost twice as much as iron, which confirms its biological significance. The level of Si in the body decreases significantly with age, and a need for its supplementation arises. The mean daily requirement for the element is 20-40 mg, and a diet does not fully provide this amount. Many plant-based supplements with a low content and low bioavailability of the element as well as preparations in the form of aqueous solutions with a high Si concentration, up to 2%, are supplied commer- cially. The target of the research was to determine the content of silicon in the bioavailable form of orthosilicic acid (H2SiO4) in dietary supplements, seawater, tap water, carbonated water and still water, tested with the colorimetric method. The silicon content in bottled waters was deter- mined to be in the range of concentrations of 1 to 20 mg dm-3, while in tap water, seawater and plant preparations it ranged from 0.2 to 1700 mg dm-3. Commercially available preparations with a high concentration of Si (0.1-2%) are characterized by a varied level of bioavailability of H2SiO4, not exceeding 20%. The colorimetric method for the determination of orthosilicic acid is well-known, but requires strict conditions to the complex to be formed. The kinetics of the steps during the reaction of complex formation, and the influence of the ambient pH on possible complications were investigated. Keywords: silicon, dietary supplement, bioavailability of orthosilicic acid. Paulina Putko, MSc, Biomedical Engineering Center, Institute of Optoelectronics, Military University of Technology in Warsaw, Gen. Witolda Urbanowicza 2, 00-908 Warsaw, Poland, e-mail: [email protected] * Financed from statutory funds. 1144 INTRODUCTION Silicon is one of the 10 most important natural elements in our body, with its content in the human body equal about 7 g, which is twice as much as the iron content. In the human organism, the highest concentration of silicon is mainly in the connective, cartilage and bone tissue, and the amount of Si in individual internal organs depends mainly on the Si content of the connective tissue. It is found in the bone-joint system, tendons, skin, walls of blood vessels, heart valves and blood, where it reaches the levels of about 10 mg dm-3. The important role of Si in the body is associated with ensuring the elas- ticity of blood vessels, counteracting the crystallization of ingredients in the urinary system, delaying the ageing process, and removing toxic substances from cells. In addition, this element positively affects the proper development of the skeleton, removes irritation and inflammation of the skin, improves the condition and prevents hair loss or brittleness of nails, it also has a cura- tive effect in cases of varicose veins, psoriasis and plaques acne (BOGUSZEWSKA et al. 2003, BAREL et al. 2005, JUGDAOHSINGH 2007). Silicon is the basic nutrient of plants and promotes toughness of roots, and is also important in the pro- cess of growth and plant resistance to disease. Particularly rich in silicon are herbs, for example, nettle, prostrate knotweed, wheatgrass, Icelandic moss, sedge or alchemilla (ZIELECKA 1996). Silicon is taken passively by plants in the form of orthosilicic acid together with water, and then it is incorporated into plant tissues, as evidenced by the presence of this element in the dry matter of plants. In addition, silicon combines with plant substances (sugars, proteins or phenolic compounds), which occur in all types of their tissues, and this prevents the fungal mushroom from penetrating into the plant. Results of the research carried out by JUGDAOHSIGH (2007) have shown that oligomers of silicic acid, unlike silicic acid, protect the human body against aluminum absorption. The inhibitory activity of silicon was also confirmed in the Belles’s syndrome tests, in which 450 mg per day of an aluminum compound and various doses of silicon contained in drinking water (59 and 118 mg dm-3 Si per day) were administered to laboratory rats for 5 weeks. As a result of the analysis of aluminum concentrations in internal organs (spleen, brain and liver), less of the examined element was found in rats whose drinking water was enriched with silicon (BELLES et al.1998, RONDEAU et al.2009). In everyday life, people are in contact with many silicon compounds, but they ingest them mainly in food. However, diatomaceous earth and silica are used as clarifying and filtering substances for example in the production of oils, margarines and beer. They can cause contamination of the final product, which is not desirable from the technological point of view, because silica -1 has been classified as a slightly toxic substance, and its LD50 is 3.16 g kg (Łukasiak, Czarobaj 2002). 1145 The concentration of silicon in drinking water should not exceed 2 mg dm-3. Many experiments by Persha et al., on the content of silicon in bottled still, low-carbon mineral and spring waters as well as in fruit juices showed that among the mineral waters selected for testing the lowest concentration of silicon was contained in the water Kinga Pienińska (3.33 mg dm-3), while the highest one was was obtained for Kryniczanka (30.05 mg dm-3). In the case of natural spring waters, the determined content of the microelement ranged from 3.34 mg dm-3 to 11.81 mg dm-3. Analyzing the results of tests on the concentration of silicon in juices, it appears that its highest content occurred in apple juices, and the richest of this element product contained 1.93 mg Si per 100 g, while the poorest in silicon was orange juice, with just 0.21 mg Si 100 g-1. Of all the studied groups of juices, the most popular were fruit juices in which the silicon content varies from 0.89 to 1.6 mg 100 g-1 (PRESHA et al. 2011). Deficiencies of silicon can cause many ailments, hence supplementation in older people becomes so important. There is a large group of various com- mercially available silicon preparations on the market, although the element they contain differs significantly in bioavailability. Silicon in the form of insoluble (mineral) is poorly absorbed, as it is estimated that about 10% of non-specialized proteins can actively activate silicon. It is believed that the only form that is available to living organisms is orthosilicic acid. Currently used dietary supplements containing silicon compounds can be divided into two groups. One comprising preparations with silicon of natural origin, containing extracts from plants rich in silicon or diatoms. The other group includes preparations containing orthosilicic acid, or silicates with various additives protecting against polymerisation (osmolytryglycerol, tau- rine, choline). The composition of alkali metal silicates with stabilizers can ensure high concentrations of the element, in the range of 0.02-1.6 mol dm-3. Twenty-fold dilution with water makes it possible to obtain silicate solutions stable for two weeks at pH 7-8. The chief purpose of this research was to compare the assimilable form of various commercially available preparations, using the colorimetric method for determinations. The influence of various reaction conditions on the forma- tion of silicon complex with molybdate- pH, equilibrium time, and complex stability was investigated. Analysis of orthosilicic acid was also carried out in selected mineral waters. The determination of the total Si content was carried out using the ICP method. The colorimetric method of the H3SiO4 content in a very wide range of concentrations enabled the monomer-dimer reaction equilibrium to be studied. General properties of silicon compounds At room temperature, silicon is a chemically inactive element because the surface of its crystallites is always covered with a thin layer of silicon dioxide. The most common forms of silicon in nature are silicic acid 1146 (from orthosilicic acid to insoluble silica) and silicates. The crystalline silica is made of SiO2 and its basic structural element is the silicon-oxygen tetra- 4- hedron [SiO4] . There are 13 polymorphic forms of crystalline silica, depend- ing on the locations of silicon-oxygen tetrahedrons. The most common types of silica are quartz and cristobalite. Both forms are also characterized by high melting point and high resistance to weak alkalis and acids. Amorphous silica is the result of the chaotic spatial location of the tetra- 4- hedrons (SiO4) . There are varieties of amorphous silica which are obtained in technological processes, such as glass fibers or quartz glass. Some of its forms come from living organisms and are commonly referred to as Biogenic Amorphous Silica. The source of BAS are both plants, diatoms, sponges as well as viruses and fungi (Łukasiak, Czarobaj 2002). The main source of different silicon compounds in soils is the wind ero- sion of primary and secondary silicates and aluminosilicates. In the soil solution, silicas occur in the form of both monosilicic acids and polysilicic acids. Orthosilic acid enacts an important role in soil because it facilitates access to certain elements necessary for plants.
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