Porphyra is a
genus of coldwater
seaweeds that grow in cold, shallow
seawater. More specifically, it belongs to
red algae phylum of laver species (from which comes
laverbread), comprising approximately 70 species.[2] It grows in the
intertidal zone, typically between the upper intertidal zone and the
splash zone in cold waters of
temperate oceans. In East Asia, it is used to produce the
sea vegetable products nori (in Japan) and gim (in Korea). There are considered to be 60–70 species of Porphyra worldwide[3] and seven around Britain and Ireland, where it has been traditionally used to produce edible
sea vegetables on the
Irish Sea coast.[4] The species Porphyra purpurea has one of the largest
plastidgenomes known, with 251 genes.[5]
Life cycle
Porphyra displays a heteromorphic
alternation of generations.[6] The
thallus we see is the
haploid generation; it can reproduce asexually by forming
spores which grow to replicate the original thallus. It can also reproduce sexually. Both male and female
gametes are formed on the one thallus. The female gametes while still on the thallus are fertilized by the released male gametes, which are non-motile. The fertilized, now
diploid, carposporangia after
mitosis produce spores (
carpospores) which settle, then bore into shells, germinate and form a filamentous stage. This stage was originally thought to be a different species of alga, and was referred to as Conchocelis rosea. That Conchocelis was the
diploid stage of Porphyra was discovered in 1949 by the British
phycologistKathleen Mary Drew-Baker for the
European species Porphyra umbilicalis.[7] It was later shown for species from other regions as well.[2][8]
Food
Most human cultures with access to Porphyra use it as a food or somehow in the diet, making it perhaps the most domesticated of the marine algae,[9] known as
laver, rong biển (
Vietnamese), nori (
Japanese:海苔), amanori (Japanese),[10]zakai, gim (
Korean:김),[10]zǐcài (
Chinese:紫菜),[10]karengo, sloke or slukos.[3] The marine red alga Porphyra has been cultivated extensively in many
Asian countries as an
edible seaweed used to wrap the rice and fish that compose the Japanese food
sushi and the Korean food gimbap. In Japan, the annual production of Porphyra species is valued at 100 billion
yen (US$1 billion).[11]
P.umbilicalis is harvested from the coasts of Great Britain and Ireland, where it has a variety of culinary uses, including
laverbread.[12] In Hawaii, "the species P.atropurpurea is considered a delicacy, called Limu luau".[12] Porphyra was also harvested by the
Southern Kwakiutl,
Haida, Seechelt,
Squawmish,
Nuu-chah-nulth,
Nuxalk,
Tsimshian, and
Tlingit peoples of the North American Pacific coast.[12]
Vitamin B12
Porphyra contains
vitamin B12 and one study suggests that it is the most suitable non-meat source of this essential vitamin.[13] In the view of the Academy of Nutrition and Dietetics, however, it may not provide an adequate source of B12 for
vegans.[14]
Species
Porphyra currently contains 57 confirmed species and 14 unconfirmed species.[15]
Following a major reassessment of the genus in 2011, many species previously included in Porphyra have been transferred to Pyropia: for example Pyropia tenera, Pyropia yezoensis, and the species from New Zealand Pyropia rakiura and Pyropia virididentata, leaving only five species out of seventy still within Porphyra itself.[16]
^
abGuiry, Michael D. (2012). Porphyra. In: Guiry, M.D. & Guiry, G.M. (2017). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway (taxonomic information republished from AlgaeBase with permission of M.D. Guiry). Accessed through: World Register of Marine Species at
http://www.marinespecies.org/aphia.php?p=taxdetails&id=143808 on 2017-09-06
^
abBrodie, J.A. and Irvine, L.M. 2003. Seaweeds of the British Isles. Volume 1 Part 3b. The Natural History Museum, London.
ISBN1 898298 87 4
^
abKain, J.M. 1991. Cultivation of attached seaweeds. in Guiry, M.D. and Blunden, G. 1992. Seaweed Resources in Europe: Uses and Potential. John Wiley and Sons, Chichester
ISBN0-471-92947-6
^Hardy, F.G. and Guiry, M.D. 2006. A Check-list and Atlas of the Seaweeds of Britain and Ireland. British Phycological Society, London.
ISBN3-906166-35-X
^Thomas, D. 2002. Seaweeds. The Natural History Museum, London.
ISBN0-565-09175-1
^Mumford, T.F. and Miura, A. 4.Porphyra as food: cultivation and economics. in Lembi, C.A. and Waaland, J.R. 1988. Algae and Human Affairs. Cambridge University Press, Cambridge.
ISBN0-521-32115-8
^Aoki, Y. and Kamei, Y. 2006 Preparation of recombinant polysaccharide-degrading enzymes from the marine bacterium, Pseudomonas sp. ND137 for the production of protoplasts of Porphyra yezoensisEur. J. Phycol.41: 321-328.
^Watanabe F, Yabuta Y, Bito T, Teng F (May 2014).
"Vitamin B₁₂-containing plant food sources for vegetarians". Nutrients. 6 (5): 1861–73.
doi:10.3390/nu6051861.
PMC4042564.
PMID24803097. A nutritional analysis of six vegan children who had consumed vegan diets including brown rice and dried purple laver (nori) for 4–10 years suggested that the consumption of nori may prevent Vitamin B12 deficiency in vegans.
^Melina V, Craig W, Levin S (2016).
"Position of the Academy of Nutrition and Dietetics: Vegetarian Diets". J Acad Nutr Diet. 116 (12): 1970–1980.
doi:
10.1016/j.jand.2016.09.025.
PMID27886704.
S2CID4984228. Fermented foods (such as tempeh), nori, spirulina, chlorella algae, and unfortified nutritional yeast cannot be relied upon as adequate or practical sources of B-12.39,40 Vegans must regularly consume reliable sources— meaning B-12 fortified foods or B-12 containing supplements—or they could become deficient, as shown in case studies of vegan infants, children, and adults.