Laminaria digitata (Oarweed)

Characteristics

Laminaria digitata is a type of large brown algae of the family Laminariaceae. It grows in sublittoral zones (fairly shallow coastal areas where sunlight reaches the ocean floor), primarily in the northern Atlantic Ocean.

This seaweed is distinguished by its digitated frond that has 3 to 8 finger-like segments when mature. Laminaria comes from the Latin lamina, meaning "blade," and refers to the blade-like-lashes of the seaweed. Digitata comes from digitus, which means "finger" in Latin, and refers to the shape of the thallus (shoots) of the seaweed, which have been compared to the shape of a human hand. Its common name is Oarweed, but it is also called tangleweed, sea tangle, sea girdle, sea ribbon, and red ware. In Ireland it is called leath and learach.

The number of fronds on each plant depends on the amount of exposure to light it receives. The size of the fronds depends on the season and the area in which it is raised, and they can grow to 1–2 meters in length in suitable conditions.

Geographical spread & harvest season in Europe

Laminaria digitata is found in cold North Atlantic and Arctic oceans. It grows naturally along most British and Irish coasts and in the North Sea, along the Scandinavian coasts. The southernmost occurrence of the species in European waters is found on the southern coasts of Brittany. This seaweed is also found in Iceland, the Faeroes, southern Greenland, the eastern coasts of North America from Hudson Straits to New York, and in Canadian Atlantic coastal waters.

Laminaria digitata is a perennial crop and lives for 4–6 years, although in some cases plants can live for up to 10 years. It grows slowly from late summer to January, and then grows more quickly from February through July. It is normally harvested in the second or third year of cultivation, with the harvest season starting in April or May and extending through October.

Nutritional content

Laminaria digitata contains abundant vitamins, minerals, and trace elements, making it an excellent food product. These include calcium, potassium, iodine, iron, carotene, protein, alginic acid, laminaran, mannitol, niacin, phosphorus, the B complex vitamins, vitamin C and many other trace elements.

Uses in food

Laminaria digitata is a good source of glutamic acid, an amino acid responsible for umami, the Japanese word used for fifth basic taste (in addition to salt, sweet, sour, and bitter). The umami flavor adds a mellow, silky taste to dishes, which is why it is extensively used in Japanese and Chinese food, particularly to make dashi, a soup stock.

It can also be eaten with vegetables such as beans and lentils, a combination that decreases their cooking time, while improving their digestibility. Oarweed is commonly consumed as a sea vegetable in snacks, flavorings, and seasonings.

In powdered form, L. digitata is a common ingredient in nutritional supplements and energy drinks.

Uses other than food

Economically, Laminaria digitata has primarily been used as a source of algin. But there are an increasingly large number of other uses throughout the pharmaceutical, medical and food industries:

• Historically, the dried stalks of L digitata, called sea-tangle tents, were used during pregnancy to induce labour.
• L. digitata is harvested offshore of France and Morocco for use in manufacturing alginic acid. It is commonly used as an ingredient in some cosmetics, particularly slimming aids and remedies for indigestion.
• The fat-burning property of the fucoxanthin present in L. digitata, in conjunction with the triglyceride absorption action of alginate, has been shown to provide relief to people with diabetes.
• Alginates are also used in manufacturing for the manufacture of paper, textiles, waterproofing, and fireproofing fabrics. They are used in the food industries to thicken, emulsify, and stabilise foods such as drinks, ice cream, and jellies.