18 Nov Nutrients of Spirulina
A nutrient is a chemical substance that an organism takes with food and water and it is necessary for this organism to live and grow and to perform metabolic functions. Nutrients include organic molecules such as carbohydrates, fats, proteins or their building blocks and vitamins as well as inorganic chemical compounds such as dietary minerals. Nutrients needed in relatively large quantities are called macronutrients and those needed in relatively small quantities are called micronutrients.
Chemical analysis of Spirulina has shown that it is an excellent source of proteins, vitamins and dietary minerals (Tables 1-3)
Table 1. Chemical composition of Spirulina platensis
(% dry mass content) (13,14)
Nucleic acids 4.2-6
Spirulina is useful in human nutrition, due to the high quality and quantity of its protein. It has the highest protein of any natural source (50-70% of its dried weight), far more than animal and fish flesh (15-25%), dried milk (35%), eggs (12%), soybeans (35%) or grains (8-14%). From a qualitative point of view, spirulina proteins are complete, since all the essential amino acids are present (an essential amino acid is an amino acid that cannot be synthesized de novo by the human organism and therefore must be supplied in the diet). The highest values (of total amino acids) are leucine, valine and isoleucine, while, the most poorly represented are methionine and cysteine which nevertheless are present more than 80% of the ideal level (**12, *13, 15). More than 100% of the daily amount of essential amino acids needed by an adult are contained in 36g of Spirulina. Daily consumption of 10g of the microalga provides about 10-14% of the Daily Recommended Dose of protein (17). The major protein constituents of Spirulina with significant health effects are the phycobiliproteins phycocyanin C and allophycocyanin (at approximately 10:1 ratio), which are proteins with linear tetrapyrrole prosthetic groups (phycocyanobilin) that in their functional state, are covalently linked to specific cysteine residues of the proteins and they form light-harvesting antenna complexes of the cyanobacteria (52). Spirulina is the only food containing phycocyanins, which represent about 15-25% of the dry biomass of the microalga. Phycocyanins have excellent antioxidant, anti-inflammatory and neuroprotective properties (52) with a large number of applications in biology, biotechnology and medicine as well as in food and cosmetic products (48-50). An important promising application of phycocyanins and phycobilin constituents of Spirulina in medicine is photodynamic therapy (*47, *51).
Table 2. Amino Acid Composition of Spirulina platensis (*12, **13, 15)
|Essential Aminoacids||mg/10 g ξηρής Σπειρουλίνας||%|
Table 3. Spirulina Vitamin and Inorganic Nutrient Content- Daily Requirements and % Daily Recommended Value (12, **13, **16)
|Vitamin/Inorganic Nutrient||Content(mg/3g)||Daily Requirements (mg)||% Daily Recommended Value|
|Folic acid (Β9)||0.0015||0.4||0.4|
|β-carotene (Provitamin A)||2.1-5.1||0.9(Provitamin Α)||–|
Spirulina contains 5-7% lipids separated into a saponifiable fraction (83%) and a non-saponifiable fraction (17%), containing essentially paraffin, pigments, terpene alcohol and sterols. A detailed analysis of Spirulina fatty acids has shown the presence of essential fatty acids (ω-3 and ω-6), which include mostly γ-linolenic acid (GLA, ω-6), and linoleic acid (ω-6). Evaluation of the composition of 19 different Spirulina strains has shown that except S.subsala, all strains contained the same fatty acids although a great diversity was observed in the fatty acid distribution among the various strains. . Predominant fatty acids were palmitic acid, GLA, linoleic acid and oleic acid. While the content of palmitic acid was constant (about 44% of total fatty acids) the content of the other fatty acids varied. Oleic acid from 1-15.5%, linoleic acid from 11-31% and GLA from 8-32% (18) Spirulina can be considered as one of the best known sources of GLA after human milk and some little used vegetable oils such as evening primrose, borage, blackcurrant seed and hemp oil. GLA play significant biological role, especially for the structure of neuronal cell membranes and therefore for brain function. Recent experimental results have shown interesting anti-cancer properies of GLA. In general, essential fatty acids play are important molecular precursors for the biosynthesis of prostaglandins, leucotrienes and thromboxanes which are major chemical mediators of inflammatory and immune reactions. Therefore, Spirulina has been proposed as a dietary complement in case of essential fatty acid deficiency. Spirulina platensis total lipids include neutral lipids, galactolipids and polar lipids. Galactolipids (mainly monogalactosyl- and digalactosyl- diacylglycerols/ MGDGs,DGDGs) contain the major percentage of GLA and they present antiinflamatory properties (75). Spirulina contains also sulfolipids, a group of polar lipids, which were shown to be effective against the HIV virus; therefore they were selected by the American National Cancer Institute for preclinical evaluation of their possible clinical usefulness against AIDS (18). Spirulina sulfoquinovosyl diacylglycerols are specific sulfolipids of great pharmaceutical importance presenting anti-cancer activity (76), strong action against HIV-1 virus (77) as well as anti-inflammatory action most probably as antagonists of PAF (Platelet Activating Factor) (78).
Spirulina non-saponifiable lipid fraction contains a small amount (less than 0.015% of dry mass) of free sterols (cholesterol, β-sitosterol, campesterol and stigmasterol), terpenes and saturated hydrocarbons. Several of the above sterols have been shown to express antimicrobial activity (13).
In general, carbohydrates constitute 15-25% of the dry weight of Spirulina. The most abundant sugar was found to be glucose. Spirulina carbohydrates are mainly branched polysaccharides, easily assimilated by the human organism, containing primarily the sugars glucose, galactose and xylose, while fructose, mannose and ramnose are present in lower amounts. Spirulina polysaccharides include lipopolysaccharides (31.6% of total sugars) and polysaccharides similar to glycogen, the main storage polysaccharide of animal cells (mainly in liver and skeletal muscle). From the nutritional standpoint, the sugar mesoinositol phosphate, which is an excellent source of organic phosphorus and inositol, occurs in considerable quantities, about eight times that of beef and several hundred times that of vegetables (15, **18, **19). It has also to be emphasized that the presence, of a sulphated polysaccharide named spirulan is of great importance for human health, since it presents strong antiviral activities, while it is able to potentiate human immune capacity. Another high Molecular Weight polysaccharide of Spirulina with strong immunomodulating activities has been recently commercialized.
The nucleic acid (DNA and RNA) content is of great nutritional importance because the biochemical degradation of their components ends by producing uric acid, since the rise of uric acid in plasma can produce kidney stones and gout attacks in the long term (13). It is generally considered that the maximum daily intake of nucleic acids is about 4g/day for an adult. Nucleic acid content of Spirulina is 2.5-4-fold higher than that of beef but much lower than that of other unicellular organisms (4-6-fold lower content than that of yeast). With an average Spirulina nucleic acid content of 5%, the daily limit of 4g represents the nucleic acid content of 80g of dry Spirulina. This amount is about eight times the recommended dose of Spirulina as food supplement. We can therefore consider with safety that the nucleic acid content of Spirulina does not pose health problems, even over long periods and at high doses. Vitamins and nutritional minerals
Spirulina contains a number of vitamins necessary for the regulation of human metabolism (Table 3). Pro-Vitamin A (beta-carotene). Vitamin A is a fat soluble vitamin. The precursor of this vitamin is pro-vitamin A or β-carotene. Main metabolic functions of this vitamin include its role in vision and in reducing of heart disease as well as its antioxidant activity. Vitamin A is the precursor of retinal which is associated visual pigments such as rhodopsin. Vitanin A deficiency has been associated with night blindness, while if occurring early in pregnancy it can induce serious damages in the nervous system. Beta-carotene (0.7-1.7 g/kg) accounts for 80% of the carotenoids present in Spirulina which are convertible into vitamin A by human organism. For adults vitamin A requirements are covered by the ingestion of 1-2g of Spirulina/day. Vitamin E (tocopherol). Vitamin E is a lipid soluble vitamin with strong antioxidant properties. It blocks the action of reactive oxygen species, such as oxygen free radicals, before they can oxidize cellular constituents, thus blocking cell damage. Dry Spirulina contains 50-190 mg/kg of vitamin E, a level comparable to that of wheat germ. Vitamin B complex. Spirulina is a perfect source for vitamins B1, B2, B3, B6, B9 and B12. It has to be emphasized the extremely high content in vitamin B12 (1.5-2 mg/kg) which is 250% higher than that of beef liver and which is difficult to obtain n a food plant diet. Vitamins Β1, Β2, Β6, Β12 and folic acid (B9) have been shown to be needed for the synthesis of several neurotransmitters. The deficiency of vitamin B12 induces anemia and neurological defects (56).
Although biological macromolecules represent the major structural and functional constituents of life many inorganic cellular constituents greatly affect human metabolism and health. These inorganic constituents or dietary minerals are the chemical elements, other than the four elements carbon, hydrogen, nitrogen and oxygen present in organic molecules, required by living organisms. Spirulina contains essential inorganic constituents and trace elements which can easily be absorbed by the human organism (Table 3). Especially the iron of Spirulina is absorbed more than 60% than that contained in food supplements and it is therefore a very good iron source for anemias. Calcium, phosphorus and magnesium are present in Spirulina in quantities comparable to those present in milk. Moreover, the high potassium content is also worth underlining because many nutritionists attack the very low potassium/sodium ratio available in the majority of food sources.
In general we have to emphasize that Spirulina may protect children from various health problems concerning development and cognitive functions from multiple vitamin and trace element deficiencies due to malnutrition (56).
Spirulina’s dark color comes from a number of natural pigments which absorb different wavelengths of sunlight. These pigments include phycocyanin a protein blue pigment, chlorophyll (its content is about 1%) a green pigment and carotenoids yellow/orange pigments (they make up 0.37% of Spirulina). About half of carotenoids are xanthophylls while the other half are various carotenes (mostly β-carotene). (12-15).
(**) Literature on the subject