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  Section: Algae » Algae and Men
 
 
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Rhodophyta

 
     
 
Content
Algae and Men
  Sources and Uses of Commercial Algae
    - Food
      - Cyanophyta
      - Rhodophyta 
      - Heterokontophyta
      - Chlorophyta
    - Extracts 
      - Agar
      - Alginate 
      - Carrageenan
    - Animal Feed
    - Fertilizers 
    - Cosmetics 
    - Therapeutic Supplements 
    - Toxin
Porphyra (Bangiophyceae) is popularly known as Nori in Japan, Kim in Korea, and Zicai in China. It is among the most nutritious macroalgae, with a protein content of 25–50%, and about 75% of which is digestible. This alga is an excellent source of iodine, other trace minerals, and dietary fibers. Sugars are low (0.1%), and the vitamin content very high, with significant amounts of vitamins A, complex B, and C, but the shelf life of vitamin C can be short in the dried product. During processing to produce the sheets of nori, most salt is washed away, so the sodium content is low. The characteristic taste of nori is caused by the large amounts of three amino acids: alanine, glutamic acid, and glycine. It also contains taurine, which controls blood cholesterol levels. The alga is a preferred source of the red pigment r-phycoerythrin, which is utilized as a fluorescent “tag” in the medical diagnostic industry.

Porphyra has been cultivated in Japan and the Republic of Korea since the 17th century, because even at that time natural stocks were insufficient to meet demand. Today Porphyra is one of the largest aquaculture industries in Japan, Korea, and China. Because of its economic importance and other health benefits, Porphyra cultivation is now being expanded to other countries.

Porphyra species are primarily intertidal, occurring mainly in temperate zones around the world, but also in subtropical and sub-Artic regions, as confirmed by its history of being eaten by the indigenous peoples of northwest America (Alaska) and Canada, Hawaii, New Zealand, and parts of the British Isles. Porphyra abbottae Krishnamurthy is a nutritionally and culturally important species of red alga used by First Peoples of coastal British Columbia and neighboring areas, down to northern California. This species, along with Porphyra torta and possibly others, is a highly nutritious food, still gathered in quantity today by the Coast Tsimshian, Haida, Heiltsuk, Kwakwaka’wakw, and other coastal peoples from wild populations in large quantities, dried and processed, and served in a variety of ways: toasted as a snack, cooked with clams, salmon eggs, or fish in soup, or sprinkled on other foods as a condiment. Common linguistic origin of the majority of names for this species among some 16 language groups in five language families indicates widespread exchange of knowledge about this seaweed from southern Vancouver Island north to Alaska. The harvesting and preparation of this seaweed is exacting and time-intensive.

It necessitates a wide range of knowledge and skills, including an understanding of weather patterns, tides, and currents; an appreciation of the growth and usable life stages of the seaweed; and a knowledge of the optimum drying locations and techniques and of the procedures for secondary moistening, chopping, and drying to achieve the best flavors and greatest nutritional value. P. abbottae is generally harvested in May. Though formerly a women’s activity, as for dihe´ harvesting by Kanembu women, both genders now participate in seaweed gathering. The postharvest preparation and handling of the seaweed is fairly labor-intensive and detailed. Once processed, seaweed is considered “an expensive and prestigious food” and is valued as a gift or trade item that is often exchanged for equally valuable products from other groups, especially on the central and northern coasts of British Columbia and Alaska. P. abbottae is valued also for its medicinal properties as gastrointestinal aid, taken as decoction or applied as a poultice for any kind of sickness in the stomach, and as orthopedic aid applied on broken collarbones.

Nearly 133 species of Porphyra have been reported from all over the world, which includes 28 species from Japan, 30 from North Atlantic coasts of Europe and America, and 27 species from the Pacific coast of Canada and United States. Seven species have been reported from the Indian coast, but they are not exploited commercially.

Porphyra grows as a very thin, flat, blade, which can be yellow, olive, pink, or purple. It can be either round, round to ovate, obovate, linear or linear lanceolate, from 5 to 35 cm in length. The thalli are either one or two cells thick, and each cell has one or two stellate chloroplasts with a pyrenoid. Porphyra has a heteromorphic life cycle with an alternation between an aploid gametophyte consisting of a macroscopic foliose thallus, which is eaten, and a filamentous diploid sporophyte called conchocelis phase. This diploid conchocelis phase in the life cycle was earlier thought to be Conchocelis rosea, a shell-boring independent organism. Understanding that these two phases were connected was a major research advance made in 1949 in Britain, when Drew demonstrated in culture that Porphyra umbilicalis (L.) Ku¨tz had a diploid conchocelis phase. Until this landmark work, cultivation of Porphyra was developed intuitively, by observing the seasonal appearance of spores, but nobody knew where the spores came from, so there was little control over the whole cultivation process. Drew’s findings completely revolutionized and transformed the Porphyra industry in Japan and subsequently throughout Asia, allowing indoor mass cultivation of the filamentous form in sterilized oyster shells and the seeding of conchospores directly onto nets for outplanting in the sea. All Japanese species of Porphyra investigated so far produce the conchocelis phase, which can be maintained for long periods of time in free culture. It grows vegetatively under a wide range of temperature, irradiances, and photoperiods, and it is probably a perennial persistent stage in the life history of many species in nature as well.

Since Drew’s time, cultivation has flourished, and now accounts for virtually all the production in China, Japan, and the Republic of Korea. Japan produces about 600,000 wet tons of edible macroalgae annually, around 75% of which is for nori. In 1999, the combined annual production from these three countries was just over 1,000,000 wet tons. Nori is a high value product, worth approximately US$16,000/dry tons. Japanese cultivation of Porphyra yields about 40,000 wet tons/year and this is processed into ca. 10 billion nori sheets (each 20 x 20 cm, 3.5–4.0 g), representing an annual income of 1500 million U.S. dollars. In the Republic of Korea, cultivation produces 270,000 wet tons, while China produces 210,000 wet tons.

Processing of wet Porphyra into dried sheets of nori has become highly mechanized, by an adaptation of the paper-making process. Wet Porphyra 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. 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. Nori 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. It can be incorporated 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 Republic of Korea it has uses similar to Japan.

Dried nori is in constant oversupply in Japan and producers and dealers are trying to encourage its use in the U.S. and other countries. Production and markets in China are expanding, although the quality of the product is not always as good as that from the Republic of Korea and Japan.

The fronds of the red alga Palmaria (Rodimenia) palmata (Florideophyceae) are known as “dulse”; they are eaten raw as a vegetable substitute or dried and eaten as a condiment in North America and Europe (Brittany, Ireland, and Iceland). Natives of Alaska consume the fronds fresh or singed on a hot stove, or add the air-dried fronds to soups and fish head stews. Palmaria is found in the eulittoral zone and sometimes the upper sublittoral. It is collected by hand by harvesters plucking it from the rocks at low tide. It is perennial and when either plucked or cut, new growth appears from the edge of the previous season’s leaf. It is harvested mainly in Ireland and the shores of the Bay of Fundy in eastern Canada, and is especially abundant around Grand Manan Island, situated in the Bay of Fundy, in a line with the Canadianthe U.S. border between New Brunswick and Maine. The harvest season here is from mid-May to mid-October. After picking, fronds are laid out to sun dry for 6–8 h; if the weather is not suitable, it can be stored in seawater for a few days, but it soon deteriorates. Whole dulse is packed for sale in plastic bags, 50 g per bag. Inferior dulse, usually because of poor drying, is broken into flakes or ground into powder for use as a seasoning. In Ireland, it is sold in packages and looks like dark-red bundles of flat leaves. It is eaten raw in Ireland, like chewing tobacco, or is cooked with potatoes, in soups and fish dishes.

Dulse is a good source of minerals, being very high in iron and containing all the trace elements needed in human nutrition, and has also a high vitamin content. In Canada, one company has cultivated it in land-based systems (tanks) and promotes it as a sea vegetable with the trade name “Sea Parsley.” It is a variant of normal dulse plants, but with small frilly outgrowths from the normally flat plant. It was found by staff at the National Research Council of Canada’s laboratories in Halifax, Nova Scotia, among samples from a commercial dulse harvester.

Chondrus crispus (Florideophyceae), the Irish moss or carrageenan moss, has a long history of use in foods in Ireland and some parts of Europe (Figure 7.3). It is not eaten as such, but used for its thickening powers when boiled in water, a result of its carrageenan content. One example is its use in making blancmange, a traditional vanilla-flavored pudding. In eastern Canada, a company is cultivating a strain of C. crispus and marketing it in Japan as hana nori, a yellow macroalga that resembles the more traditional Japanese nori that is in limited supply from natural resources because of overharvesting and pollution. First introduced to the Japanese market in 1996, the dried product, to be reconstituted by the user, was reported to be selling well at the end of 1999, with forecasts of a market valued at tens of millions of U.S. dollars. It is used in macroalgae salads, sushimi garnishes, and as a soup ingredient.

Fresh Gracilaria (Florideophyceae) has been collected and sold as a salad vegetable in Hawaii (USA) for several decades. It is known as Ogo, ogonori, or sea moss. The mixture of ethnic groups in Hawaii (Hawaiians, Filipinos, Koreans, Japanese, and Chinese) creates an unusual demand and supply has at times been limited by the stocks available from natural sources. Now it is being successfully cultivated in Hawaii using an aerated tank system, producing up to 6 tons fresh weight per week. Limu manauea and limu ogo are both sold as fresh vegetables, the latter usually mixed with raw fish. In Indonesia, Malaysia, Philippines, and Vietnam, species of Gracilaria are collected by coastal people for food.
 
Frond of Chondrus crispus.
FIGURE 7.3 Frond of Chondrus crispus.

In southern Thailand, an education programme was undertaken to show people how it could be used to make jellies by boiling and making use of the extracted agar. In the West Indies, Gracilaria is sold in markets as “sea moss”; it is reputed to have aphrodisiac properties and is also used as a base for a non-alcoholic drink. Gracilaria sp. contains (wet weight basis): 6.9 ±0.1% total proteins, 24.7±0.7% crude fiber, 3.3±0.2% total lipids, and 22.7±0.6% ash. It contains 28.5±0.1 mg of vitamin C per 100 g of wet biomass, 5.2±0.4 % mg of β-carotene per 100 g of dry weight, which corresponds to a vitamin A activity of 865 µg. According to standard classification adopted by AOAC (Association of Official Analytical Chemists), this can be considered a very high value of vitamin A activity for a food item, which makes Gracilaria a potential source of β-carotene for human consumption.

In Chile, the demand for edible macroalgae has increased and Callophyllis variegata (carola) (Florideophyceae) is one of the most popular (Figure 7.4). Its consumption has risen fromzero in 1995 to 84 wet tons in 1999. This red macroalgae has a promising future due to its high commercial value, which in 2001 was at about US$30 kg-1d.w. However, knowledge of its biology is limited and research project have been funded for the management of the natural resources and opportunities for cultivation.
 
Frond of Callophyllis variegata.
FIGURE 7.4 Frond of Callophyllis variegata.

 
     
 
 
     




     
 
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