Dulse (Palmaria palmata)
Common Names
Dulse, dillisk, red dulse, sea lettuce.
Natural Habitat
Intertidal zones of northern Atlantic and Pacific coasts, in depths of up to 16 to 60 feet.
Key Components
Carbohydrates, including a rare short-chain carbohydrate, floridoside, which can comprise up to 30% of this seaweed’s dry weight.1 It also contains polyphenols, polyunsaturated fatty acids, essential and trace minerals, and vitamins.
Overview
Dulse is a reddish brown marine algae that grows in the intertidal zones of the northern Atlantic and, to a lesser extent, Pacific coastlines. It gets its Latin name, Palmaria palmata, from its palmate shape with fingerlike fronds. Dulse has a disc-shaped base that attaches itself to rocky ocean beds, mussels, or to other species of algae. Young plants are often thin; more mature plants are often leathery. It is found most often in the intertidal zone (the area between low and high tides).
Dulse has a rich heritage in both Irish and Icelandic traditions. Icelandic sagas of the 11th century mentioned dulse, and regulations were enforced in the 13th century for the harvesting of dulse. This red seaweed goes back equally far in Irish lore; a poem about the responsibilities of monks mentions gathering dillisk (dulse) from rocky shores. In the early 18th century, Irish botanist Caleb Threlkeld referred to it in his reference book on the flora of Ireland, Synopsis Stirpium Hibernicarum. He described its common use in the culture of the day: “But in Dublin men chew it like Tobacco when dry, carrying it in their Pockets for that end, which destroys worms, and gives a relish to Beer, as Anchovies and Olives to Wine.”2 More recently, it was reputed to be a good hangover remedy. Today, Ireland produces about 20 tons of dry dulse for domestic markets.3 It is readily available in health food stores and at local markets and fairs, especially in Northern Ireland. It is used as an ingredient in soups, stews, chowders, fish dishes, breads, condiments, and is often eaten fresh or dried as a snack food.
Like many species of seaweed, dulse is nutrient-dense. An 8-gram portion contains 2.7 grams of fiber, about 11% of the reference nutrient intake. It also contains essential and trace minerals such as calcium, potassium, magnesium, sodium, copper, iron, iodine, and zinc. An 8-gram portion contains approximately 10% of the reference nutrient intake of calcium, 16% of potassium and magnesium, 8% of sodium, 16% of copper, and 74% of iron. It is especially rich in iodine, with an 8-gram portion containing over 3000% of the reference nutrient intake. Dulse is also an excellent source of vitamin A, with 8 grams containing 91% of the reference nutrient intake. It is also a good source of B12, with one serving containing 65% of the reference nutrient intake. Fats comprise as much as 2% of the total dry weight, including a good percentage of polyunsaturated fatty acids (PUFAs). The ratio of omega-3 to omega-6 fatty acids in dulse is believed to be near optimal.4 A study published in Lipids in Health and Disease looked closely at the polyunsaturated fatty acids in dulse. Researchers found that dulse contains both arachidonic acid and eicosapentaenoic acid (EPA), both beneficial for health. They estimate that the ratio of omega-6 to omega-3 is close to the optimum 1:1, with an especially high concentration of EPA.5
Other benefits of dulse have been identified, most notably its potential for antioxidant activity. Researchers have found that dulse has the potential to neutralize free radicals over a long period of time; this research suggests that this may be helpful in extending product shelf life.6 Researchers believe the antioxidant function comes from dulse’s high polyphenol content.7 Further investigation reveals that dulse’s antioxidant power is related to how much UV sunlight it is exposed to. The more natural UV exposure it gets, the greater its antioxidant reducing activity.8
Perhaps most exciting are research findings that suggest dulse may be of benefit in the fight against cancer. One in vitro study found that, in a dose-dependent manner, dulse inhibited the proliferation of adenocarcinoma cells.9 In another study that evaluated the effects of five seaweeds on human cervical cancer cells, dulse performed the best. It inhibited cancer cell proliferation by up to 78%. Researchers attributed this anti-proliferative effect to dulse’s high polyphenol content.10
1 Algaebase.org, accessed June 21, 2013.
2 Algaebase.org, accessed June 21, 2013.
3 Algaebase.org, accessed June 21, 2013.
4 MacArtain, P., et al. Nutritional Value of Edible Seaweeds. Nutrition Reviews. 2007. 65 (12), 535-543.
5 van Ginneken, V., et al. Polyunsaturated fatty acids in various macroalgal species from north Atlantic and tropical seas. Lipids in Health and Disease. 2011. 10 (104).
6 Yuan, Y., et al. Antioxidant activity of dulse (Palmaria palmata) extractevaluated in vitro. Food Chemistry. 2005. 91, 485-494.
7 Yuan, Y. and Walsh, N.A. Antioxidant and antiproliferative activities of extracts from a variety of edible seaweeds. Food and Chemical Toxicology. 2006. 44 (7), 1144-1150.
8 Yuan , Y., et al. Extracts from dulse (Palmaria palmata) are effective antioxidants and inhibitors of cell proliferation in vitro. Food and Chemical Toxicology. 2005. 43, 1073–1081.
9 Yuan , Y., et al. Extracts from dulse (Palmaria palmata) are effective antioxidants and inhibitors of cell proliferation in vitro. Food and Chemical Toxicology. 2005. 43, 1073–1081.
10 Yuan, Y. and Walsh, N.A. Antioxidant and antiproliferative activities of extracts from a variety of edible seaweeds. Food and Chemical Toxicology. 2006. 44 (7), 1144-1150.
Research
1. Antioxidant activity of dulse (Palmaria palmata) extract evaluated in vitro
Yuan, Y., et al. Food Chemistry. 2005. 91, 485-494.
Researchers tested a soluble fraction of dulse for antioxidant activity. Commonly used DPPH and ABTS antioxidant assay tests demonstrated this substance’s potential to neutralize free radicals over a long period of time. Other indicators of the extract’s antioxidant function were its polyphenol content and its ability to scavenge hydroxyl radicals. Researchers believe that because the dulse extract demonstrates prolonged antioxidant function, it may be especially useful in products where a longer shelf life is desired.
2. Extracts from dulse (Palmaria palmata) are effective antioxidants and inhibitors of cell proliferation in vitro
Yuan , Y., et al. Food and Chemical Toxicology. 2005. 43, 1073–1081.
Researchers looked at the seaweed dulse (Palmaria palmate) for its antioxidant potential and its ability to inhibit tumor cell growth. They used two dulse samples that, because of their differing locations, were exposed to varying amounts of natural UV radiation from sunlight. Sample 1, which was grown in an area with reduced UV exposure, had lower antioxidant reducing activity. Sample 2, which had greater natural UV exposure, had greater antioxidant reducing activity. Both samples, in a dose dependent manner, inhibited the proliferation of adenocarcinoma (cancer) cells in vitro.
3. Antioxidant and antiproliferative activities of extracts from a variety of edible seaweeds
Yuan, Y. and Walsh, N.A. Food and Chemical Toxicology. 2006. 44 (7), 1144-1150.
Researchers looked at the ability of five seaweed extracts, including dulse (Palmaria palmata) on human cervical cancer cells. The cancer cells were treated in vitro for 72 hours with soluble fractions of methanol extracts of each variety. The dulse extract performed the best, inhibiting up to 78% of cancer cell proliferation. Further analysis also revealed that the antioxidant reducing activity of dulse was highest, as was dulse’s polyphenol content. Researchers also observed that dulse’s high polyphenol content was associated with its high anti-proliferative function.
4. Polyunsaturated fatty acids in various macroalgal species from north Atlantic and tropical seas
van Ginneken, V., et al. Lipids in Health and Disease. 2011. 10 (104).
Polyunsaturated fatty acids (PUFA) have long been associated with cardiovascular health, mental health, and anti-inflammatory activity. In this study, researchers evaulated the PUFA content of seven varieties of seaweed, including dulse. Omega-3 and omega-6 fatty acids were identified, ranging from 2 to 14 mg/g of dry matter. Total fat content was between 7 and 45 mg/g of dry matter. In terms of total fatty acids, the seaweed varieties were made up of 8 to 63% omega 3 fats, 3 to 32% omega 6 fats, and 3 to 56% omega-9 fats. Both red and brown seaweeds (including dulse) contain arachidonic and eicosapentaenoic (EPA) acids. Researchers conclude that seaweeds such as these are a renewable source of PUFAs, and contain a healthy 1:1 ratio of omega 6 to omega 3 fatty acids. Dulse (Palmaria palmata) also contains a high ratio of EPA.
5. Nutritional value of edible seaweeds
MacArtain, P., et al. Nutrition Reviews. 2007. 65 (12), 535-543.
A recent study analyzed eight different varieties of seaweed, including dulse (Palmaria palmata), for nutrient content. In the context of daily reference nutrient intakes (RNI), researchers measured the nutrients in one 8-gram serving. A serving of dulse contains 2.7 grams of fiber, approximately 11% of the RNI. It contains 74 mg of calcium (10% of RNI), 584 mg potassium (16%), 49 mg magnesium (16%), 127 mg sodium (8%), 0.2 mg copper (16%), 6.4 mg iron (74%), and 5 mg iodine (3650%). Dulse also contains vitamins, two in particular worth mentioning. It contains 638 mcg of vitamin A per 8 gram serving, 91% of the RNI, and 0.92 mcg of B12, or 65% of the RNI. Trace amounts of the B vitamins are also present. Dulse contains small amounts of polyunsaturated fats close to the optimum omega-3:omega-6 ratio.
