World Aquaculture 13 Table 1. Protein content of some potential seaweed (Fleurence 1999) Seaweed species Protein content (% of dry mass) Palmaria palmata 8 - 35 Porphyra tenera 33 - 47 Ulva lactuca 10 - 21 Ulva pertusa 20 - 26 Laminaria digitata 8 - 15 Fucus sp. 3 - 11 Ascophyllum nodosum 3 – 15 Seaweeds as a Potential Lipid Source Seaweed lipids have a higher proportion of essential fatty acids than any land plants. The fatty acids of seaweeds generally have linear chains, an even number of carbon atoms, and one or more double bonds. In particular, seaweeds can be a source of essential fatty acids, such as eicosapentaenoic acid, C 20:5 w3 fatty acids. However, the total lipid content in seaweeds is less than 4 percent. It has also been reported that the fatty acids of certain seaweeds have antiviral activity. Green seaweeds are rich in oleic and alpha-linoleic acids, whereas the red macroalgae have a high EPA content (Table 2). Seaweeds as a Source of Essential Vitamins and Minerals Inasmuch as seaweeds are grown on an environment rich in various nutrients, their proximate analysis has shown a good result with respect to the vitamin and mineral composition. The important macronutrients available abundantly in seaweeds are Na, Ca, Mg, K, Cl, S and P whereas the micronutrients in seaweeds includes I, Fe, Zn, Cu, Se, Mb, Fl, Mn, B, Ni and Co. The brown algae like those belonging to kelps are the richest source of iodine (1500-8000 ppm). The seaweed Fucus contains iodine in range of 500-1000 ppm. The green and red macroalgae has relatively lower iodine content (100-300 ppm). Seaweeds are considered natural sources of hydrosoluble and liposoluble vitamins, such as thiamine and riboflavin, ßcarotene and tocopherols. The red and brown algae contain a good amount of carotenes (provitamin A) in range of 20-170 ppm, whereas the vitamin C content in these seaweeds is 300-500 ppm. Other vitamins are also found in seaweeds, the most important being vitamin B12 which is absent in most land plants. Seaweeds as Feed Binders The best known component of the seaweed derived industry is that of the phycocolloids, the gelling, thickening, emulsifying, binding, stabilizing, clarifying and protecting agents known as carrageenans, alginates and agars. The binding property of seaweed meal depends on the ability of its extract to form highly viscous solutions and to gel in the presence of polyvalent cations. The sulphate group and its location in the molecule determines gelling capacity (gel strength is less if the sulfate ester is at carbon 6). Kappa-carraggenan from K. alvurezii has slightly higher sulfate content than agar. This makes agar a stronger binder than carrageenan (Penaflorida and Golez 1996). However, kappa-carrageenan is sulfated at C-4 and with enough K+ ions (from other feed ingredients); it can give gel strength similar to that of agar. Seaweeds as a Source of Pigments and Attractants Red seaweed may also have a huge potential for use as a natural colorant in salmonid fishes and may replace the synthetic astaxanthin and canthaxanthin. Red seaweeds contain a particular protein called phycoerythrin. At the Table 2. Lipid content of some important seaweed (Sanchez-Machado et. al. 2004) Seaweed Lipid content Himanthalia elongata 0.93 Sacchorhiza polyschides 0.70 Laminaria ochroleuca 0.92 Undaria pinnatifida 1.05 Porphyra sp. 1.03 Palmaria sp. 1.80 moment, phycoerythrin is obtained from the microalgae Porphyridium cruentum in which the pigment can represent up to 50 percent of the protein fraction. The seaweed Ascophyllum nodosum is host to cytokinins, auxin-like gibberellins, betaines, mannitol and organic acids, which serve as feed attractants. Antioxidants in Seaweeds The seaweed, Kappaphycus alvarezzi, which has gained importance especially in the Indian mariculture, has good nutritive and antioxidant properties. Seaweeds are known to contain reactive antioxidant molecules, such as ascorbate and glutathione (GSH) when fresh, as well as secondary metabolites, including carotenoids (α- and β-carotene, fucoxanthin, astaxanthin), mycosporine-like amino acids (mycosporine-glycine) and catechins (catechin, epigallocatechin), gallate, phlorotannins (phloroglucinol), eckol and tocopherols (α-, χ-, δ- tocopherols). Brown-algal polyphenols and phlorotannins also have antioxidants compounds. Some active antioxidant compounds frommarine algae were identified as phylopheophylin in Eisenia bicyclis, phlorotannins in Sargassum kjellamanianum and fucoxanthin in Hijikia fusiformis. The seaweeds Euchema kappaphycus, Gracilaria edulis, Acanthophora spicifera and Sargassum marginatum, Padina tetrastomatica and Turbinaria conoides are known to posses antioxidant properties. The seaweed extract of G. acerosa possesses high antioxidant activity. It can prevent the increase of lipid peroxide (LPO) in serum, liver and spleen of fish.
RkJQdWJsaXNoZXIy MjExNDY=