Nori (Porphyra) health benefits and its usage as human food

This is the purplish-black seaweed often seen wrapped around a small handful of rice in sushi. It comes largely from cultivation in Japan, the Republic of Korea and China. In Japan’s list of products from marine culture, Nori (Porphyra) has the highest production, followed by oyster, yellowtail and wakame. It has a lot of health benefits and it is widely used as human food.

Nori (Porphyra) grows as a very thin, flat, reddish blade, and is found in most temperate intertidal zones around the world, illustrated by its history of being eaten by the indigenous people of northwest America and Canada, Hawaii, New Zealand and parts of the British Isles.

It is among the most nutritious seaweeds. The Nutritional Content of Porphyra Umbilicalis is in the below table.

While Nori (Porphyra) can be collected by hand from natural sources, most is now derived from cultivation.It has an unusual life cycle that was not understood until the early 1950s. Until then it had been cultivated but nobody knew where the spores came from, so there was little control over the whole cultivation process.

The seaweed, as we know it, sheds spores and these settle on mollusk shells: in nature it is any nearby; in cultivation they are deliberately placed beneath the blades of the seaweed. An alternate generation of filamentous algae develops from these spores and burrow into the surface of the shell; this is called the conchocelis stage. With lowered light (shorter days) and lower temperature, more, but different, spores form from the filaments and these are allowed to settle onto nets. It is these spores that develop into the blades of this seaweed The nets are placed in the ocean in such a way that they are exposed to air for a few hours a day.It is reasonably resistant to some drying out, but the pest seaweeds that try also to grow on the nets do not survive. The nets were originally set up in intertidal flat areas, but as space become short, a new system of floating nets in deeper water was devised. The spores germinate on the nets and grow into new blades of Nori.

Attempts have been made to cultivate Nori (Porphyra) in non-Asian countries, notably the west and east coasts of United States of America. Cultivation on the west coast-Puget Sound in Washington State- was successful but became unviable commercially when residents of the shore areas objected to the presence of seaweed farms and access to sufficient space to expand the pilot farm was refused. In Maine, on the east coast, cultivation problems with indigenous species of this seaweed slowed progress, but as these were being overcome, regulatory issues between landholders and commercial fishermen again delayed progress. In the meantime, the company was reorganized, decided to develop other marine biotechnology interests and to discontinue the Nori project.

Japanese cultivation of this kind of seaweed yields about 400,000 wet ton/year and this is processed into ca 10 billion nori sheets (each 20x20 cm, 3.5-4.0g), representing annual income of US$1,500 million. In the Republic of Korea, cultivation produces 270,000 wet tons, while China produces 210,000 wet tons.

Processing of wet Nori into dried sheets has become highly mechanized, rather like an adaptation of the paper-making process. The wet one is rinsed, chopped into small pieces and stirred in a slurry. It is then poured onto mats or frames, most of the water drains away, and the mats run through a dryer. Rate of drying is carefully controlled by adjusting conveyer speed and temperature. The sheets are peeled from the mats and packed in bundles of ten for sale. This product is called hoshi-nori, which distinguishes it from yaki-nori, which is toasted. Toasted nori is pre-toasted and sold in sealed packages; in use it may be brushed with a mixture of soy sauce, sugar, sake and seasonings.

Nori (Porphyra) is used mainly as a luxury food. It is often wrapped around the rice ball of sushi, a typical Japanese food consisting of a small handful of boiled rice with a slice of raw fish on the top. After a short baking (slight toasting or baking brings out the flavor), It can be cut into small pieces and sprinkled over boiled rice or noodles. It can be in corporate into soy sauce and boiled down to give an appetizing luxury sauce. It is also used as a raw material for jam and wine. In China it is mostly used in soups and for seasoning fried foods. In the Repulic of Korea it has similar uses to Japan, except that a popular snack with beer is hoshi-nori that has been quickly fried in a pan with a little oil.

References

(1) MacArtain, Nutritional value of edible seaweeds

http://li123-4.members.linode.com/files/Nutritional%20Value%20of%20Edible%20Seaweeds.pdf

(2) Schultz Moreira at al, Effects of Undaria pinatifida, Himanthalia elongate and Porphyra umbilicalis extracts on in-vitro glucosidase activity and glucose diffusion

(3) Marine medicinal foods (book) edited by Se-Kwon Kim

A guide to the seaweed industry- Dennish J.McHugh (Page 73-76)