Wakame (Undaria pinnatifida) uses in human food

Wakame (Undaria pinnatifida) has a high total dietary fiber content, higher than Nori or Kombu. Like the other brown seaweeds, the fat content is quite low. Air-dried form has a similar vitamin content to the wet seaweed and is relatively rich in vitamin B group, especially nicacin; however, processed form products lose most of their vitamins. Raw form contains appreciable amounts of essential trace elements such as manganese, copper, cobalt, iron, nickel and zinc, similar to Kombu and Hijiki. Its nutritional content is as below.

Wakame (Undaria pinnatifida) is an annual plant with a life cycle similar to Laminaria. It has an alternation of generations with the large seaweed as the sporophyte and a microscopic gametophyte as the alternate generation. Some wild material is collected and used locally, but all the commercial products are from cultivated plants. Cultivation methods are very similar to those used for Laminaria, although some of the temperature tolerances are different. The Republic of Korea is the largest producer of Wakame. There, seeding starts in April; string is wound around frames and these are immersed in tanks. Fresh, mature plants (sporophytes) are air-dried in the shade for about an hour and then immersed in the tanks so spores are released and settle on the strings. The tanks are exposed to natural light and the seawater in the tanks is changed monthly; the water temperature must be kept below 25^oC or the gametophytes may die. The gametophytes mature, fertilizer eggs form on the strings and develops into your sporophytes. During September-October the sea water drops below 23^oC and the frames or strings are moved to protected intermediate culture areas so that the young plants can adapt to open seawater conditions.

Once the young plants are 1-2 cm long, the strings are removed from the frames and would around a rope that is suspended by floats and anchored to the bottom at each end. However, a variation from the Laminaria cultivation is that the rope long-lines are suspended 2-3 m below the surface. In sheltered bays, the ropes are placed 10m apart; in open waters, where there is more movement, the single ropes are assembled into a grid pattern using connecting ropes to hold the long-lines about 2 m apart. Harvesting is in two stages. First the plants are thinned out by cutting them off at a point close to the rope. This is done by pulling the rope over the edge of a boat, cutting and dragging the plant into the boat. The remaining plants on the rope have plenty of space and continue to grow. Harvesting finishes in April. In Japan, the seeded strings are often cut into small lengths and inserted in the twist of a rope that is then hung vertically from a floating rope, much the same as is done with Laminaria. Harvesting in southern Japan is from March to May, but around Hokkaido it is from May to July.

Cultivation has also been undertaken in France. Here the above methods were found to be inappropriate because the high nutrient concentrations in the water allowed a large variety of other plant and animal life (epiphytes) to grow on the fames holding the strings. The constant cleaning of the frames proved to be too expensive. Instead, the alternate generation, the gametophytes, are formed and maintained in a sterile laboratory medium. One month before out-planting the gametophytes are brought to maturation. After fertilized eggs (zygotes) are formed, the solution with the suspended zygotes is sprayed onto a nylon line that is wound around a frame. The zygotes germinate and young sporophytes begin to grow on the fames, which are free of epiphytes. The sporophytes are out-planted on floating ropes in the usual way.

After harvesting, the plants are washed with seawater, the freshwater, the central midrib is removed and the pieces are dried in the sun or a hot air dryer; this is suboshi wakame. However, this product often faded during storage because various enzymes are still active. To overcome this, another process can be used in which the fresh seaweed is mixed with ash from wood or straw, spread on the ground for 2-3 days, then placed in a plastic bag in the dark. The alkalinity of the ash inactivates the enzymes. The plants are washed with seawater, then freshwater to remove the salt and ash, the midrib is removed and the pieces are dried. This is haiboshi wakame and it keeps its deep green color for a long time.

Blanched and salted Wakame (Undaria pinnatifida) is the major product. Fresh one is plunged into water at 80^oC for 1 minute and cooled quickly in cold water. About 30kg of salt per 100kg of seaweed are mixed and stored for 24 hours. This dehydrates it; excess water is removed and the seaweed stored at -10^oC. When ready for packaging, it is taken from storage, the midribs are removed and the pieces placed in plastic bags for sale. It is a fresh green color and can be preserved for long periods when stored at low temperatures.

Cut wakame is a very convenient form, used for various instant foods such as noodles and soups. It is one of the most popular dried products. It is made from blanched and salted form which is washed with freshwater to remove salt, cut into small pieces, dried in a flow-through dryer and passed through sieves to sort the different sized pieces. It has a long storage life and is a fresh green color when rehydrated.

In the Republic of Korea, wakame is enjoyed as an ingredient in soybean and other soups, as well as vinegar seaweed salads. In recent times there has been an overproduction of new products, such as seaweed salad, pre-cooked form, powdered form for use as a condiment and further expansion of the uses of cut, dried form.

Wakame (Undaria pinnatifida) is more popular in the Republic of Korea than in Japan, although the market in Japan has expanded. It is traditionally regarded as a luxury food in both countries although overproduction has led to reduced prices in recent times. The Republic of Korea produces ten times more Undaria than Laminaria; it produces four times more Undaria than Japan. Production in China has apparently increased, as has its exports to Japan. In 2001, the Chinese seaweed industry agreed to reduce exports of wakame to Japan, beginning in April 2002. Japanese wakame producers agreed to support Chinese seaweed growers in finding other overseas markets and expanding demand in China. Japan imported 180,000 tons and wakame from China from mid-1999 to mid-2000, a 2.4-fold increase from four years earlier. Production in Japan halved during that one year period.

References and sources:

A guide to the seaweed industry- Dennish J.McHugh (Page 81-83)

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http://www.aulamedica.es/nh/pdf/7381.pdf

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http://www.ncbi.nlm.nih.gov/pubmed/24837949

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http://www.ncbi.nlm.nih.gov/pubmed/25344759 (free text not available)