Seaweeds or sea vegetables are a group of marine macroalgae that are found growing on the rock surfaces or other hard surfaces along the coastal areas and sea bottoms. They belong to three different groups, on the basis of thallus (algal body) colour: brown algae (e.g. kelps), red algae (e.g. Gelidium) and green algae (e.g. green laver). Brown and red algae are marine in nature and therefore they are very large seaweeds while green algae are common in fresh waters and are comparatively small in size.
Brown colour of the brown algae is due to the presence of fucoxanthin, a xanthophyll pigment. Red colour of the red algae is due to the presence of pigments called phycoerythrin and phycocyanin. Green colour of the green algae is due to the presence of chlorophylls just like the higher plants. Food reserves in brown algae are polysaccharides, sugars, and higher alcohols. In red algae, food reserves are in the form of floridean starch and floridoside. Green algae reserves food as starch just like higher plants. In brown algae, cell walls are made up of cellulose and alginic acid. Cell walls in red algae are made up of cellulose and complex polysaccharides such as agars and carrageenans. In green algae, cell walls are made up of cellulose.
Seaweeds are now used as multifunctional foods in many parts of the world. Seaweeds are considered as functional foods because of the presence of high amounts of minerals and vitamins as well as some beneficial bioactive compounds in them. A functional food produces a beneficial effect in human body by increasing the welfare and decreasing the risk of diseases. When it comes to the matter of health, prevention is better than cure and functional foods are preventative than curative.
Seaweeds are suitable for mass production owing to the fact that they are autotrophic, marine macroalgae and require only the water-dissolved carbon dioxide and nutrients for its growth. They require no or little external resources for its mass production. Despite these positive factors, the commercial cultivation of seaweeds as food is not yet picked up in many countries. Currently, Asian countries, particularly China, Japan and Korea dominate the global seaweed production. France, UK, Chile, Philippines, Indonesia, Norway, USA, Canada and Ireland are also producing seaweeds in considerable quantities.
Seaweeds are produced for two major food purposes: for direct human consumption and for processing for further food applications such as stabilizing, gelling and thickening agents to be used in food and confectionery industry.
Seaweeds are directly consumed as raw (e.g. as salads and sandwich ingredients) or cooked form such as pickles, and vegetables. Dried and powdered seaweeds are used as seasoning and food flavoring agents. Jelly derived from certain seaweeds is used as thickening agent in ice creams, soups, marmalades etc. Phycocolloids such as alginates, agar and carrageenan present in seaweeds are extracted and used for food processing purposes.
Seaweeds are used for preparing various nutraceuticals or food supplements. Food supplements have important health benefits. Certain bioactive compounds derived from seaweeds are used as therapeutic agents in pharmaceutical industry. Seaweeds are also used as organic manure, compost, and as a meal for poultry and cattle. Seaweeds are used for the extraction of industrial gums and chemicals and also for manufacturing cosmetics.
With the advent of organic food and organic farming revolution, seaweeds are now increasingly becoming popular as a naturally-grown vegetable. It is also gaining popularity the world over as an organic super food.
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