7. HUMAN USES OF ALGAE

Transcription

1 7. HUMAN USES OF ALGAE Algae are a source for viable and inexpensive carotenoids, pigments, proteins, and vitamins that can be used for the production of nutraceuticals, pharmaceuticals, animal feed additives, and cosmetics. Nowadays, about 10 7 tons of algae are harvested each year by algal biotechnology industries for different purposes. Table 2 summarizes commercially exploited algae and the corresponding products or applications. HUMAN FOOD Cyanophyta The high digestibility of cyanobacteria cells is due to the lack of cellulose, unlike the majority of algae, facilitates their use for human consumption. Nostoc sphaeroides Dried Nostoc spp. Balls are sold in Asian markets; they are stir-fried sautéed with oysters, and used in soups and as thickeners for other foods. 62

2 Nostoc flagelliforme is a terrestrial cyanobacterium. N. flagelliforme called as Facai (hair vegetable) in Chinese because of its hair-like appearance. Spirulina. There are two species, Arthrospira platensis and Arthrospira maxima. Arthrospira is cultivated worldwide; used as a dietary supplement as well as a whole food; and is also available in tablet, capsules, liquids and powder form. Arthrospira platensis located essentially in Mexico (where it is called tecuitlatl) and in Africa (Figure 1) where it is called dihe. FIGURE 1 Harvesting, drying and preparation of Arthrospira of dihe on the shore of Lake Kossorom. Microalgae Chlorella is the only green microalga (Chlorophyta) which forms a part of human diet. It is a potential food source because it is high in protein and other essential nutrients; when dried, it is about 45% protein, 20% fat, 20% carbohydrate, 5% fibre, and 10% minerals and vitamins. It is also abundant in calories and vitamins. Massproduction methods are now being used to cultivate it in large artificial ponds. Macroalgae The main reason for seaweeds consumption is their nutritional value which include The presence of some soluble, metabolized carbohydrates in seaweeds. Note that the structural carbohydrates of seaweeds are largely indigestible. The protein content of many of the edible seaweeds is 20-25% dry weight. Seaweeds are an excellent source of vitamins, including vitamin C at levels equivalent to citrus fruits, and vitamins A, D, B 1, B 12, E, riboflavin, niacin, pantothenic acid, and folic acid. Seaweeds provide all the required trace elements needed in human nutrition. Trace elements include iron, zinc, cobalt, chromium, molybdenum, nickel, tin, vanadium, fluorine, iodine, etc. Source of dietary fibers.. 63

3 The high content of poly unsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA), arachidonic acid (ARA), and docosahexaenoic acid (DHA) in some species. The attractive flavour, taste, colour, and texture of some species. A list of 160 species of seaweeds is eaten by humans (25 Chlorophyta, 54 Phaeophyceae, and 81 Rhodophyta). Table 5 summarizes edible algae and the corresponding food item. ANIMAL FOOD Many evaluation studies have shown the suitability of algal biomass as a feed supplement. Mainly the Spirulina and, to some extent, Chlorella are used in this domain for many types of animals: cats, dogs, aquarium fish, ornamental birds, horses, poultry, cows and breeding bulls 64

4 Macroalgae Seaweeds may be fed directly to cattle as fodder, but commercially they are harvested, dried, and ground into meals which are added as supplements to prepared feed. Macroalgae meal: dried macroalgae that has been milled to a fine powder. The macroalgae used for meal must be freshly cut, as drift macroalgae is low in minerals and usually becomes infected with mould. Benefits o As a binder for wet food used in fish farming: wet feed usually consists of meat and fish wastes mixed with dry additives containing extra nutrients, all formed together in a doughy mass. When thrown into the fish ponds or cages it must hold together and not disintegrate or dissolve in the water. A binder is needed; so macroalgae meal is a cheaper choice (instead of a technical grade of alginate). o Increase the iodine content of the poultry eggs. o In poultry feeds the carotenoids produce deeply colored yolks in the eggs. o In cows it increases the milk production of 6.8% that lead to 13% more income. o Ewes fed macroalgae meal over a 2 yr period maintained their weight much better during winter feeding and also gave greater wool production. o Boost the immune system of some animals Fresh macroalgae There is also a market for fresh macroalgae as a feed for abalone. Microalgae use in aquaculture systems Many marine animals cannot synthesize certain essential long-chain fatty acids in quantities high enough for growth and survival and thus depend upon algal food to supply them. Over the last four decades, several hundred microalgae species have been tested as food, but probably less than 20 have gained widespread use in aquaculture. Successful strains for culture included Isochrysis galbana, Isochrysis sp., Pavlova lutheri, Tetraselmis suecica, Pseudoisochrysis paradoxa, Chaetoceros calcitrans, and Skeletonema costatum. Isochrysis sp. (T.ISO). Microalgae, are utilized in aquaculture as live feeds for all growth stages of bivalve mollusks (e.g., oysters, scallops, clams, and mussels), for the larval/early juvenile stages of abalone, crustaceans, and some fish species, for zooplankton used in aquaculture food chains such as rotifers and/or Artemia, which are then fed on to later larval stages of crustacean and fish larvae. Quality of micro-algae used for aquaculture purposes Microalgae must possess a number of key attributes to be useful aquaculture species. They must be of an appropriate size and shape for ingestion. they must have a good nutrient composition, digestibility (related to cell wall structure and composition), They must have rapid growth rates, be amenable to mass culture, be stable in culture to any fluctuations in temperature, light, and nutrients. the algae must be free of toxins that might be transferred up the food chain. 65

5 The growth of animals fed a mixture of several algal species is often superior to that obtained when feeding only one algal species. A particular alga may lack a nutrient, while another alga may contain that nutrient and lack a different one. In this way, a mixture of both algal species supplies the animals with an adequate amount of both nutrients. Green water A common procedure during the culture of both larval fish and prawns is to add microalgae (i.e., green water ) to culture systems together with the zooplankton prey. Addition of the microalgae to fish larval raising tanks can improve the production of larvae, though the exact mechanism of action is unclear. Theories include: a. light attenuation (i.e., shading effects), which have a beneficial effect on larvae, b. maintenance of the nutritional quality of the zooplankton c. an excretion of vitamins or other growth-promoting substances by algae, and d. Maintenance of NH 3 and O 2 balance has also been proposed, though this has not been supported by experimental evidence. Most likely, the mechanism may be a combination of several of these possibilities. The most popular algae species used for green water applications are N. oculata and T. suecica. Harvesting and preserving microalgae In most cases, it is unnecessary to separate micro-algae from the culture fluid. Excess and off-season production may, however, be concentrated and preserved. Highdensity algal cultures can be concentrated by either chemical flocculation or centrifugation. For chemical flocculation, products such as aluminum sulphate and ferric chloride are used to coagulate cells which are either precipitate to the bottom or float to the surface. Recovery of the algal biomass is then accomplished by, siphoning off the supernatant or skimming cells off the surface. Due to the increased particle size, coagulated algae are no longer suitable as food for filter-feeders. Centrifugation Cells are centrifuged as a thick algal paste, which is then resuspended in a limited volume of water. FERTILIZERS There is a long history of coastal people using macroalgae, especially the large brown macroalgae, to fertilize nearby land. Generally, beach-washed macroalgae (Drift weed) is collected, although farmers sometimes cut macroalgae exposed at low tide. Seaweeds versus manure Seaweeds have adequate amounts of potassium and nitrogen, but are low on phosphate. In comparison, farmyard manure has only onethird the potassium, a similar amount of nitrogen, and three times the amount of phosphates. Seaweeds are also rich in trace elements and may contain hormones and growth regulators. Seaweed fertilizer have the advantage of being free from weeds and pathogenic fungi. 66

6 Are macroalgae extracts an economically attractive alternative to NPK fertilizers? Perhaps not when used on their own, but when used with NPK fertilizers they improve the effectiveness of the fertilizers, so less can be used, with a lowering of costs. Then there are always those who prefer an organic or natural fertilizer, so macroalgae extracts probably have a bright future. PRODUCTION OF VALUABLE (USEFUL) PRODUCTS FROM ALGAE POLYSACCHARIDES CYANOBACTERIA produce three types of extracellular matrix consisting mainly of polysaccharides, which have unique bio- and physicochemical characteristics. Most of them are composed of at least ten different monosaccharides and contain pentoses, which have not been observed in other prokaryotic polysaccharides. Little work has been devoted to potential applications of marine cyanobacterial polysaccharides. MICROALGAE produce many different types of polysaccharides, which may be a costituent of the cell wall as in unicellular red algae. Paramylon is the term used for granules of the reserve polysaccharide of Euglena and euglenoids in general. Paramylon consists of -1,3-glucan, a linear polysaccharide found in the cell walls of many bacteria, plants, and yeasts. MACROALGAE PHYCOCOLLOIDS Agar Agar, a general name for polysaccharides extracted from some red algae, is built up of alternating D- and L-galactopyranose units. The name agar is derived from a Malaysian word agar-agar, which literally means macroalgae. The genera Gelidium (Figure 12), Gracilaria, Hypnea and Pterocladia of the Rhodophyceae are the main producers of these materials. Agar finds its widest use as a solid microbiological culture substrate. Modern agar is a purified form consisting largely of the neutral fraction known as agarose; the nonionic nature of the latter makes it more suitable for a range of laboratory applications. Agar in a crude or purified form also finds wide usage in the food industry where it is used in various kinds of ices, canned foods, and bakery products. FIGURE 12 Frond of Gelidium sp. FIGURE 13 Frond of Macrocystis pyrifera. 67

7 Alginates (Alginic acid and its salts) This sulphated polysaccharide is obtained from the brown seaweeds, especially from species of Fucus, Macrocystis, Ascophyllum and Laminaria (Phaeophyceae). Alginates are cell-wall constituents, help large seaweeds to cope with mechanical stress generated by waves and currents. Alginates make up some 30-40% of the dry weight of brown seaweeds. Alginic acid is a copolymer of mannuronic and guluronic acids. Sodium alginate has been used o as a thickening paste for colors in printing textiles. o as stabilizers in the manufacture of ice cream, giving a smooth texture and body o It is also used in cosmetics and pharmaceuticals. o The most significant property of sodium alginate is the ability to remove heavy metals strontium and lead from the body without seriously affecting the availability of Ca, Na, K or other lighter metals in the body. Calcium alginate o Calcium alginate, has been used in the manufacture of a medical dressing very suitable for burns and extensive wounds where a normal dressing would be extremely difficult to remove; the calcium alginate is extruded to make a fiber which is then woven into a gauze-like product. When applied to either a wound or burn, a network is formed around which a healthy scab may form; the bandage may be removed with a sodium chloride solution, which renders the alginate soluble in water. o Alginates are also used as glazing and sizing paper, special printers inks, paints, cosmetics, insecticides, and pharmaceutical preparations. Carrageenan Carrageenan is a general name for polysaccharides extracted from certain kinds of red algae which are built up, in contrast to agar, from D-galactopyranose units only. Carrageenan are produced by species of Kappaphycus, Eucheuma, Chondrus, Gigartina and Iridea (Rhodophyta). Carrageenan is used in the food industry as an emulsifier, particularly in dairy products; as a size in the textile and leather industries; and as an emulsifier in the pharmaceutical industry. 68

8 Table summarizes commercially exploited algae and the corresponding extract. COSMETICS Extract of algae is often found on the list of ingredients on cosmetic packages, particularly in face, hand, and body creams or lotions. Cosmetic products, sometimes show on their labels that the contents include marine extract, extract of alga, macroalgae extract or similar. This usually means that one of the hydrocolloids extracted from macroalgae has been added. Alginate or carrageenan could improve the skin moisture retention properties of the product. ALGAE IN MEDICINE Seaweeds have been extensively used in the traditional medicines of maritime nations as vermifuges, anaesthetics, and ointments, as well as for the treatment of coughs, wounds, gout, goitre, hypertension, venereal diseases, cancer, and a variety of other ills. As with most folk remedies, some are worthless while others have a substantial basis in their content of bioactive compounds. In the latter category is the use of o Digenia simplex (Rhodophyta) which contains a potent vermifuge, kainic acid; o iodine content of Laminaria (Phaeophyta) prevents goitre. o The vitamin and mineral content of marine algae also are potentially important in the prevention of other dietary insufficiency diseases. o Crude extracts of many species of algae contain substances with antibiotic properties against bacteria, fungi, and viruses. 69

9 o Antiviral compounds reported in red algae include polysaccharides containing D- glycosyl groups, which are apparently active in the control of herpes viruses. o Many seaweeds contain sterols and related compounds, which are antagonistic to cholesterol in mammalian systems and may reduce elevated blood pressure associated with atherosclerosis. o Extracts of Sargassum and Laminaria inhibited the growth of sarcoma and leukaemia cells in mice. o A number of specific compounds of algal origin have been purified and characterized and are being used experimentally in medicine. The saxitoxins produced by the paralytic shellfish poisoning (PSP) dinoflagellates are used in neurobiological research. Kainic acid is also neurotoxic and causes the breakdown of nerve dendrites: it is useful for its ability to mimic the effects of Huntington's chorea. It is also used in studies on epilepsy. o Marine algae produce a wide variety of hemagglutinins, a substance that causes red blood cells (RBCs) to agglutinate. One hemagglutinins obtained from Ptilota plumosa, is specific to human B blood group and hence has some diagnostic uses. o Carrageenan is has been used in the treatment of peptic ulcers. o The abilities of carrageenans and alginates to form metal salts have suggested their use as non-toxic chelating agents in the treatment of heavy metal and radionucleotide poisonings. PIGMENTS Algae are characterized by the presence of different kinds of pigments (in addition to chlorophyll a), which are responsible for their characteristic red, brown, blue-green and yellow colors. These pigments have promising potential as food dyes, because many red and blue pigments currently in use are thought to be carcinogens. Other advantages are their intense color, their high solubility in water, and their stability to changes in ph. Their application in cosmetics is also of great potential. Carotenoids Xanthophylls, are yellow to orange pigments used as food dyes, especially in the pigmentation of chicken skin, egg yolk, and fish (e.g., salmon). Canthaxanthin is also used as a tanning agent. -carotene -carotene is commercially the most important pigment. -Carotene is used primarily as a yellow food coloring and, being a source of vitamin A, as a component of health foods and animal feeds. Also, in humans and animals above-average ingestion of - carotene predisposes to a lower incidence of certain types of cancer. Algal milking Most microalgal products are secondary metabolites that are produced when growth is limited. The continuous removal of secondary metabolites from cells thereby enables the biomass to be reused for the continuous production of these highvalue compounds. Such process is called algal milking. The milking process can be applied to different algae and different products, Dunaliella salina, for the recovery -Carotene, Haematococcus pluvialis for the recovery astaxanthin, and different marine microalgae for Polyunsaturated fatty acids (PUFA). 70

10 Milking β-carotene Algal cells accumulate -carotene to protects them against the deleterious effects of high light intensity. When cultivated under appropriate conditions, the green microalga Dunaliella salina and D. bardawil accumulate more than 10% of their dry weight as -carotene. Recently, a new method was developed for milking β-carotene from D. salina. In this technique, cells are first grown under normal growth conditions and then stressed by excess light to produce larger amounts of β-carotene. At this stage, a biocompatible organic phase is added and the β-carotene is extracted via continuous recirculation of a biocompatible organic solvent (lipophilic compound) through the aqueous phase containing the cells. Because the cells continue to produce β -carotene, the extracted product is continuously replaced by newly produced molecules. Therefore, the cells are continuously reused and do not need to be grown again. In contrast to existing commercial processes, this method does not require the harvesting, concentrating, and destroying of cells for extraction of the desired product. The general application of this process would facilitate the commercialization of microalgal biotechnology and development of microalgal products. POLYUNSATURATED FATTY ACIDS (PUFAS) PUFAs, docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and Arachidonic acid (ARA) are gaining increasing importance as valuable pharmaceutical products and ingredients of food owing to their beneficial effect on human health. At present, PUFAs are produced commercially from fish oil, but this is an insufficient source of these products and microalgae provide an optimal lipid source of PUFAs. The heterotrophic marine dinoflagellate Crypthecodinium cohnii has a lipid content greater than 20% dry weight and is known for its ability to accumulate fatty acids that have a high fraction (30 50%) of DHA. Lipids are important components of algal cell membranes but also accumulate in globules in other parts of the cells. Milking can be used for DHA production by C. cohnii. In this process, cells are first grown under the correct growth conditions, after which they are stressed to produce higher concentrations of DHA. Eicosapentaenoic acid EPA Microalgae represent one of the most promising EPA producers. Many Eustigmatophyceae, such as Nannochloropsis sp. and Monodus subterraneus, and Bacillariophyceae species contain a considerable amount of EPA. An EPA production potential has been found in the genus Nitzschia (especially N. alba and N. laevis). It was reported that the oil content of N. alba was as high as 50% of cell dry weight and the EPA comprises 4 5% of the oil. EPA are effective in reducing levels of plasma lipids and lipoproteins and in ameliorating coronary heart disease, arthritis, and inflammatory ailments. Arachidonic acid (ARA) is a highly unsaturated fatty acid that is rarely found in higher plants. In marine red microalga Porphyridium, arachidonic acid constitutes as much as 36% of the total fatty acids. Thus, Porphyridium has been suggested as a source of arachidonic acid. In addition to being an essential fatty acid in the human diet, arachidonic acid is the natural precursor of a large family of structurally related C20 compounds that include prostaglandins, thromboxanes, leukotrients, and prostacyclins, all of which are potent biological regulators. 71