Oceans cover approximately 71 percent of the earth’s surface (362 million square km) and contain 95 percent of the habitat space on the planet. The marine environment comprises approximately half of the total global biodiversity. Seaweeds are one of the constituents of natural resources globally used for human welfare. Seaweed is the common term used to refer large marine algae growing in the shallow waters along the ocean shores. There are about 8000 species of seaweeds along the world’s coastal lines. In general seaweeds inhabit about 2% of the sea floor. Ecologically seaweed account for food and shelter for marine life. Seaweeds are used as human food, livestock feed and fertilizer for land crops in many countries. More than 160 species of sea vegetables commonly known as seaweeds are consumed throughout the world. Seaweeds can be consumed directly as raw, dried or cooked. Seaweeds are eaten for their food value, flavours, colours and textures and are typically combined with other types of food. Edible seaweeds include Porphyra (Nori), Rodymenia (Dulse), Laminaria(Kombu), undaria (Wakame) and Ulva (sea lettuce). Edible seaweeds have been shown to be high in essential pigments, vitamins, minerals, trace elements, proteins and phytochemicals as well as healthy dietary fibers and fats.
Worldwide consumption of seaweeds
Seaweed is consumed in many traditional European societies, in Iceland and western Norway, the Atlantic coast of France, northern and western Ireland, Wales and some coastal parts of South West England as well as Nova Scotia and Newfoundland. Traditionally, sea vegetables have been more commonly eaten in Asian cultures. In many countries in Asia notably in China, Japan, Korea and Indonesia, seaweed products are important dietary resources, which constitute a substantial part of the total food intake (staple food). In Philippines, Burma and Vietnam several species of seaweeds are eaten as a salad or in one form or another. The most commonly consumed seaweeds which grow in both the Atlantic and Pacific oceans are alaria, arame, hijiiki, nori, dulse and several kinds of kelp. Porphyra sp. which is commercially known as nori or laver is most widely consumed among edible red seaweed worldwide (Watanable et al 1999). Nori is commonly eaten by the Japanese. The brown seaweed Sargassum (Gulfweed, sea holly) is used in soups and soy sauce.
Definition of seaweeds
Edible seaweeds are algae that can be eaten and used in the preparation of food. It Typically contains high amounts of fiber and they contain a complete protein. They may belong to one of several groups of multicellular algae: the red algae, green algae and brown algae (ref: en.wickipedia.org).
Kinds of seaweeds
Seaweeds are plants, though less complex ones than land plants. Without roots or intricate tissues, seaweed must absorb nutrients from the sea water. To survive, they form root-like parts to attach themselves to rocks or other stable items. Seaweeds are mainly classified into 3 major classes based on their pigmentation namely brown, red and green algae which are referred to as phaeophyceae, Rhodophyceae and Chlorophyceae respectively (Khan et al. 2010). Three basic classes of pigments found in marine algae are chlorophylls, carotenoids and phycoerythrin. Green seaweeds such as sea lettuce mainly contain chlorophyll. Red seaweeds which include dulse, laver,nori, agar and Irish moss have red pigment, phycoerythrin. Brown seaweeds such as kelp, kombu, alaria, arame, wakame , seapalm and hiijiki depend on brown pigments from other carotenoid
Proximate composition of seaweeds
Seaweeds are high in ash (37-46%) and dietary fibers (25-40%) and low in lipid content (0.29-1.11%) on dry weight basis. The protein content of many seaweeds ranges between 4 and 25% of the dry weight. Generally the protein content of brown algae is low (3-15% of dry weight) compared with that of green (10-26% of dry weight) and red algae (35-47% of dry weight) (Fitzgerald et al. 2011). The lipids present in seaweeds are rich in omega-3 polyunsaturated fatty acids in particular EPA and to a lesser extent DHA, which are important to human health. Seaweeds contain 33-62% total fibers on a dry weight basis. The sulphated polysaccharides present in red and brown algae act as dietary fibers. The major seaweed colloids include agar, algin, carrageenan, and related colloids. These phycocolloids are materials such as gelatine, pectin and starch that have the property of forming gels. Algin is produced from brown seaweeds, while agar and carrageenan are from red algae. The phycocolloids are used as thickeners, humectants, coagulants, bulking agents, flocculation agents and in the preparation of antibiotic carriers. Agar finds much use in bakery products, confectionary making and in puddings, creams and jellied products. Seaweed powders generally contain 10 to 30% minerals, 20 to 45% proteins and up to 40% soluble fibers.
Popular edible seaweeds
The red seaweed, Nori is rich in iodine and iron and quite high in protein. It is also a good source of vitamins C and A, potassium, magnesium and riboflavin (B2) and it is low in fat. Another red seaweed, Dulse is highly nutritious containing protein (10 to 20%), magnesium, iron and B-carotene. Carrageenan and agar are extracted routinely from red algae. Irish moss is rich in retinol and minerals. It is widely used in all sorts of food products because it has emulsifying and jelling properties. The green seaweed, Wakame contains fucoxanthin, calcium, iron, natural sodium and vitamin C. The brown seaweeds include such familiar forms as rock seaweeds, kelps and sargassum. The brown seaweeds are major sources of iodine. In addition to iodine, the brown seaweed kelp (Kombu) also provides iron, magnesium and folate (vitamin B9). Kelp is used to be the main source for preventing goitre and treating thyroid conditions. Sea lettuce and sugar kelp are the two seaweeds popularly eaten by humans. Seaweeds represent one of the most nutritious plant foods. In Asian culture, seaweeds have always been of particular interest as food sources. Seaweeds are ones that can be used in a whole range of ways: as salads, in soups, for sushi, in deserts, in bread, as snacks and in candy or as herbs and flavour enhancers. Seaweeds are most commonly used in soups, as salad garnishes and as a seasoning (in flake forms). Seaweeds are available in health food stores in dried, powder, flake and granular forms.
Health benefits of seaweeds
Edible seaweeds are ideal sources of chemical compounds for improving health and well-being of humans. Several bioactive substances with antimicrobial and cytotoxic activities have reported from seaweeds. Tumour reductions, inhibition of cancer cell proliferation, free radical scavenging and significant antioxidant activity have been exhibited by red and brown seaweeds. The sulphated polysaccharides found in some of the brown seaweeds are being explored as antiviral agents and as aids in preventing blood clots. Sodium alginate found in brown seaweeds has the ability to protect the surface membranes of stomach and intestine. It acts as a haemostatic agent and has tried in the treatment of esophagitis and urolithiasis. Fucoidan, a polysaccharide found in brown algae has shown promising antiviral, immunomodulating and antibacterial activities. Fucoidan also inhibits the angiogenesis and proliferation of human cancer cells. Phlorotannins (polyphenols) from brown algae have been shown to possess multiple physiological activities such as antioxidant, anticarcinogenic, antibacterial, anti-inflammatory and antiallergic properties. Taurine is an amino acid present in high concentration in red algae. Taurine acts as an antioxidant and reduces serum lipids thereby prevents atherosclerosis and coronary heart disease. Calcium phosphate in seaweeds helps to reduce osteoporosis by nourishing the bones. The high content of potassium in seaweed is good for the heart and kidneys. Seaweed nourishes the membranes, making it good for nervous disorders, skin conditions, colds and constipation. The chromium content in seaweeds helps to control blood sugar levels. In general seaweed intake may strengthen the immune system, reduce cholesterol and improve metabolism and digestion. Consumption of seaweed is helpful in combating fatigue caused by slow thyroid activity. Seaweed intake support thyroid function. Dietary intake of brown algae is effective for curing goitre because of their iodine content.
Seaweeds are rich sources of some important minerals and vitamins.