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Nutritional Value |
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Seaweed draws an extraordinary wealth of mineral elements from the sea that can account for up to 36% of its dry mass. This percentage offers a wide variety of minerals, i.e. macronutrients such as sodium, calcium, magnesium, potassium, chlorine, sulphur and phosphorus, as well as trace elements essential for avoiding deficiencies, such as iodine, iron, zinc, copper, selenium, molybdenum, and many other elements such as fluoride, manganese, boron, nickel and cobalt.
Two of these elements are particularly valuable, i.e. iodine and calcium, both of which are sorely lacking in the world's population. The all-time champion for iodine content is brown algae, with dry kelp ranging from 1500 to 8000 ppm (parts per million) and dry rockweed from 500 to 1000 ppm. In most instances, red and green algae have lower contents (100 to 300 ppm dry), but remain high in comparison to "standard" sources.
Seaweed is one of the richest plant sources of calcium, with content sometimes reaching 7% of dry matter in macro-algae and as high as 25 to 34% in encrusting red algae (Lithothamnion).
Protein content in seaweed varies somewhat. It is low in brown algae at 5-11% of dry matter, but comparable in quantitative terms to legumes at 30-40% of dry matter in some species of red algae. Green algae, which are still not harvested much, also have a significant protein content, i.e. up to 20% of dry matter. Spirulina, a micro-alga, is well known for its very high content, i.e. 70% of dry matter.
Seaweed contains a rich cocktail of all the vitamins. The main ones are provitamin A in the form of beta- and alpha-carotene found in red and brown algae, with contents of 2 to 17 mg/100 g dry; vitamin C in red and brown algae, with contents ranging from 50 to 300 mg/100 g dry - equivalent to the tomato; and vitamin E in brown algae. B-group vitamins are generally well represented. An unusual feature is that seaweed contains B12, which is not the case for land plants.
Seaweed's lipid content is very low, ranging from 1 to 5% of dry matter, although seaweed lipids have a higher proportion of essential fatty acids than land plants.
Green algae, whose fatty acid make-up is the closest to higher plants, have a much higher oleic (C 18 : 1) and alpha linoleic (w3 - C18 : 3) acid content, the latter being essential to man along with linoleic acid.
Red algae have a high 20-carbon polyunsaturated fatty acid content, particularly the famous EPA (w30 - C20 : 5), which is most unusual, as these fatty acids are basically found in animals. Arachidonic acid (w6 - C20) is also well represented. They also contain 18-carbon polyunsaturated fatty acids (linolenic or linoleic).
In brown algae, fatty acid distribution is fairly comparable, with a higher linolenic acid concentration.
Seaweed has a high total dietary fiber content (32% to 50% of dry matter).
Among the insoluble fibers, there is a low percentage of cellulose and Floridean starch, particularly in red algae. Insoluble fibers are usually associated with reducing passage times through the colon.
The soluble fiber fraction accounts for 51% to 56% of total fibers in green (ulvans) and red algae (agars, carrageenans and xylans) and for 67% to 87% in brown algae (laminarans, alginates and fucans).
Soluble fibers are generally associated with hydration performance, i.e. absorption, retention and swelling, which affect the food bolus's passage through the stomach and small intestine, and can have cholesterol-lowering and hypoglycaemic effects.
Agars, carrageenans, ulvans and fucans are hardly broken down by contact with human intestinal bacteria; xylans and laminarans are fully and quickly broken down, producing a large amount of short-chain fatty acid; alginates are partly broken down. Oligomers produced in this manner have displayed bifidogenous
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