5. HUMAN USES OF ALGAE INTRODUCTION Microalgae and macroalgae have been utilized by man for hundreds of years as food, fodder, remedies, and fertilizers. Ancient records show that people collected macroalgae for food as long as 500 B.C. in China and one thousand of years later in Europe. In addition to direct consumption, agars and carrageenans extracted from red macroalgae and alginates from brown macroalgae and microalgae have been included in a remarkable array of prepared food products, serving mostly to modify viscosity or texture. Microalgae 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. Table 1 summarizes commercially exploited algae and the corresponding nutraceutical.

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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. − Nostoc flagelliforme is a terrestrial cyanobacterium. N. flagelliforme called as

“Facai” (hair vegetable) in Chinese because of its hair-like appearance. − 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. 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, B1, B12 , 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.. − 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.

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A list of 160 species of seaweeds is eaten by humans (25 Chlorophyta, 54 Phaeophyceae, and 81 Rhodophyta). The principal genera consumed are: RHODOPHYTA Porphyra (Bangiophyceae) is popularly known as Nori in Japan, Kim in Korea, and Zicai in China,. Nori 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. The characteristic taste of nori is caused by the large amounts of three amino acids: alanine, glutamic acid, and glycine.

Palmaria (Rodimenia) palmata (Florideophyceae) known as “dulse” (Figure 2); they are eaten raw as a vegetable substitute

FIGURE 2 Palmaria palmata FIGURE 3 Frond of Chondrus crispus. Chondrus crispus (Florideophyceae), the Irish moss or carrageenan moss (Figure 3) 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. It also used in macroalgae salads and as a soup ingredient.

Gracilaria (Florideophyceae) when fresh, it is known as Ogo, ogonori, or sea moss. Gracilaria has been collected and sold as a salad vegetable in Hawaii (USA) for several decades.

Limu manauea and limu ogo are both sold as fresh vegetables, the latter usually mixed with raw fish.

Callophyllis variegata (carola) (Florideophyceae) This red macroalgae is one of the most popular (Figure 4) edible macroalgae in Chile.

FIGURE 4 Frond of Callophyllis variegata.

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HETEROKONTOPHYTA Alaria esculenta, is a large brown kelp (Figure 5). It is known as winged kelp. It has a wide distribution in cold waters and does not survive above 16°C. China is the largest producer of edible macroalgae, harvesting about 5 million wet tons annually. Laminaria japonica (Figure 6) is a large macroalga, usually 2–5 m long, but it can grow up to 10 m in favorable conditions. It requires water temperatures below 20°C. Kombu is the Japanese name for the dried macroalgae that is derived from a mixture of Laminaria species where it is used in everyday food

FIGURE 5 Frond of Alaria esculenta. FIGURE 6 Frond of Laminaria japonica. Undaria sp. Called wakame, together with Laminaria sp. it is one of the two most economically important edible algae. U. pinnatifida is the main species cultivated (Figure 7). Wakame products is used for various instant foods such as noodles and soups, and its consumption is very popular.

FIGURE 7 Frond of Undaria pinnatifida.

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Hizikia fusiforme is another brown algae popular as food in Japan and the Republic of Korea known as Hiziki. It is collected from the wild in Japan and cultivated in the Republic of Korea. Cladosiphon okamuranus This brown macroalga is harvested from natural populations around the southern islands of Japan and consumed as Mozuku. CHLOROPHYTA Monostroma (Figure 9) and Enteromorpha (Figure 10) are the two green macroalgae genera cultivated in Japan, and known as aonori or green laver.

FIGURE 9 Frond of Monostroma latissimum. FIGURE 10 Frond of Enteromorpha sp. Ulva sp. is known as sea lettuce, as fronds may be convoluted and have an appearance rather like lettuce. It can be collected from the wild and added to Monostroma and Enteromorpha as part of aonori Caulerpa lentillifera (Figure 11) and Caulerpa racemosa are the two edible green algae used in fresh salads and known as sea grapes or green caviar.

FIGURE 11 Frond of Caulerpa lentillifera.

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Table 5 summarizes edible algae and the corresponding food item.

MICROALGAE Chlorella is the only green microalga which forms a regular part of human diet. ANIMAL FOOD Macroalgae The food value of seaweeds to animals is essentially as for humans. Wild animals (foxes, deer, rabbits, and bears) have been reported to feed on seaweeds, and in Europe and North America cattle, sheep and horses are frequently grazed in the intertidal. 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. It is stored in sealed bags because it picks up moisture if exposed to air. The macroalgae used for meal such as Laminaria, Ascophyllum. and Fucus must be freshly cut, as drift macroalgae is low in minerals and usually becomes infected with mould.

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Benefits

o As a binder 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 coloured 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. These include the brown macroalgae Macrocystis pyrifera, and the Pacific dulse Palmaria mollis, the red macroalgae Gracilaria edulis and Porphyra as well as the green macroalgae, Ulva lactuca. Feeding trials showed that abalone growth is greatly improved by high protein content, and this is attained by culturing the macroalgae with high levels of ammonia present. 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. Microalgae, are utilized in aquaculture as live feeds − for all growth stages of bivalve molluscs (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.

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 bivalve culture included Isochrysis galbana, Isochrysis sp., Pavlova lutheri, Tetraselmis suecica, Pseudoisochrysis paradoxa, Chaetoceros calcitrans, and Skeletonema costatum. Isochrysis sp. (T.ISO), P. lutheri, and C. calcitrans are the most common species used to feed the larval, early juvenile, and broodstock (during hatchery conditioning) stages of bivalve molluscs; these are usually fed together as a mixed diet. Many of the strains successfully used for bivalves are also used as direct feed for crustaceans (especially shrimp) during the early larval stages, especially diatoms such as Skeletonema spp. and Chaetoceros spp. Benthic diatoms such as Navicula spp. and Nitzschia are commonly mass-cultured and then settled onto plates as a diet for grazing juvenile abalone. Isochrysis sp., P. lutheri, T. suecica, or Nannochloropsis spp. are commonly fed to Artemia or rotifers, which are then fed on to later larval stages of crustacean and fish larvae. Nutritional value of micro-algae Microalgae must possess a number of key attributes to be useful aquaculture species. • They must be of an appropriate size and shape for ingestion, for example, from 1

to 15 µm for filter feeders; 10 to 100 µm for grazers and readily digested.

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• They must have rapid growth rates, be amenable to mass culture, and also be stable in culture to any fluctuations in temperature, light, and nutrients.

• digestibility (related to cell wall structure and composition), • Finally, they must have a good nutrient composition, including an absence of

toxins that might be transferred up the food chain. Microalgae that have been found to have good nutritional properties — either as monospecies or within a mixed diet — include C. calcitrans, C. muelleri, P. lutheri, Isochrysis sp., T. suecica, S. costatum, and Thalassiosira pseudonana. 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. Microalgae constituents The gross composition of 16 species of microalgae is compared in Table 6. Although there are marked differences in the compositions of the micro-algal classes and species, protein is always the major organic constituent, followed usually by lipid and then by carbohydrate. Expressed as percentage of dry weight, the range for the level of protein, lipid, and carbohydrate are 12-35%, 7.2-23%, and 4.6-23%, respectively. The content of poly unsaturated fatty acids (PUFA), in particular eicosapentaenoic acid (EPA), arachidonic acid (ARA), and docosahexaenoic acid (DHA), is of major importance in the evaluation of the nutritional composition of an algal species to be used as food for marine organisms. Significant concentrations of EPA are present in the diatom species (Chaetoceros calcitrans, C. gracilis, S. costatum, T. pseudonana) and the haptophyte (prymnesiophytes) Platymonas lutheri, whereas high concentrations of DHA are found in the prymnesiophytes (P. lutheri, Isochrysis sp.) and Chroomonas salina. Micro-algae can also be considered as a rich source of ascorbic acid (0.11-1.62% of dry weight).

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6

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The nutritional value of micro-algae can vary considerably according to the culture conditions. For example the effect of the composition of the culture medium on the proximate composition of various species of micro-algae is demonstrated in Table 7. The protein content per cell, which is considered as one of the most important factors determining the nutritional value of micro-algae as feed in aquaculture, was found to be more susceptible to medium-induced variation than the other cellular constituents.

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The nutritional value of micro-algae can vary considerably according to the growth phase. Microalgae grown to late-logarithmic growth phase typically contain 30–40% proteins, 10–20% lipids and 5–15% carbohydrates. When cultured through to stationary phase, the proximate composition of microalgae can change significantly; for example, when nitrate is limiting, carbohydrate levels can double at the expense of protein.

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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 larval 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 NH3 and O2 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. High-density algal cultures can be concentrated by either chemical flocculation or centrifugation. Products such as aluminum sulphate and ferric chloride cause cells to coagulate and 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. The resulting slurry may be stored for 1-2 weeks in the refrigerator or frozen. In the latter case, cryoprotective agents (glucose, dimethylsulfoxide) are added to maintain cell integrity during freezing. However, cell disruption and limited shelf-life remain the major disadvantages of long-term preserved algal biomass. 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 one-third 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 manures have the advantage of being free from weeds and pathogenic fungi. The practice was o wet macroalgae are mixed with sand, let it rot, and then dig it in. o sun-dried and transported to other areas. o dried, milled as macroalgae meal and sold as soil additives.

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o composted and then used for growing plants. The addition of the compost increased water holding capacity and plant growth, so composting simultaneously solved environmental pollution problems and produced a useful organic fertilizer.

o Maerl is the common name of a fertilizer derived from calcareous red algae. It is marketed for soil improvement, mainly to replace lime as an agricultural soil conditioner to reduce soil acidity.

o Liquid fertilizers Several brands of liquid fertilizer based on extracts or suspensions of whole or part of seaweeds are commercially available and are used in many applications. Most of the extracts contain several types of plant growth regulators such as cytokinins, auxins, and betaines, which may be responsible for the improvements of the yield. When applied to fruit, vegetable, and flower crops, some improvements have included higher yields, increased uptake of soil nutrients, increased resistance to some pests, improved seed germination, and more resistance to frost.

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, especially in horticulture, 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 as Porphyridium sp. and Rhodella sp., or be present inside the cell, as in the Euglenophyceae. The polysaccharides of Rhodophyta are highly sulfated and consist mainly of xylose, glucose, and galactose. Paramylon is the term used for granules of the reserve polysaccharide of Euglena and euglenoids in general. Paramylon consists of β-1,3-glucan, a linear polysaccharide found in the cell walls of many bacteria, plants, and yeasts. MACROALGAE PHYCOCOLLOIDS Agar, alginate (derivative of alginic acid), and carrageenan are three hydrocolloids (phycocolloids) that are extracted from various red and brown macroalgae. A hydrocolloid is a non-crystalline substance with very large molecules. They are cell wall components which are soluble in hot water and relatively insoluble in cold. Agar, alginate, and carrageenan are used in the food, cosmetic. and pharmaceutical industries, as emulsifiers, as gelling agents, and to stabilize certain products, such as ice-cream (they inhibit the formation of large ice crystals, allowing the ice-cream to retain a smooth texture). The gelling properties of agar can be extracted with hot water from a red macroalgae.

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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 non-ionic 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.

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.

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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.

Table summarizes commercially exploited algae and the corresponding extract.

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COSMETICS Extract of algae is often found on the list of ingredients on cosmetic packages, particularly in face, hand, and body creams or lotions. Thalassotherapy has come into fashion in recent years, especially in France. In thalassotherapy, macroalgae pastes, made by cold-grinding or freeze-crushing, are applied to the person’s body and then warmed under infrared radiation. Sometimes additional freezing is done with liquid nitrogen that makes the frozen material more brittle and easier to grind or crush. The result is a fine green paste of macroalgae. This treatment, in conjunction with seawater hydrotherapy, is said to provide relief for rheumatism and osteoporosis. Paste mixtures are also used in massage creams, with promises to rapidly restore elasticity and suppleness to the skin. Cosmetic products, such as creams and lotions, 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. 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 A wide range of algal extracts were 'strikingly unproductive' in anticancer tests, extracts of Sargassum and Laminaria however 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 haemagglutinins; one, 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.

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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.

Much of the potential of the algae in medicine has yet to be explored. The broad range of compounds found in tropical seaweeds offers particularly exciting prospects for the future. 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. β-carotene β-carotene is commercially the most important pigment. β-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 β-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 high-value compounds. Such process is called algal milking. The milking process can be applied to different algae and different products, Dunaliella salina, for the recovery β-Carotene, Haematococcus pluvialis for the recovery astaxanthin, and different marine microalgae for Polyunsaturated fatty acids (PUFA). Milking β-carotene Algal cells accumulate β-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 β-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, the second, 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. The extraction of the product will enhance its synthesis. 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

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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) and eicosapentaenoic acid (EPA) 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. Microalgal growth and fatty acid formation is affected by medium composition and environmental conditions (e.g., carbon sources). Lipid production occurs under growth-limiting conditions; during linear growth, the cells are stressed owing to nutrient limitation and therefore produce more lipids. Also the concentration of DHA, and the lipid quality, is negatively affected by increases in lipid concentration. The highest quality lipid it obtained when glucose is used as the carbon source, and when the cell concentration and lipid content of the cells are the lowest. Milking can be used for DHA production by C. cohnii. In this process, cells are first grown under the correct conditions for growth, after which they are stressed to produce higher concentrations of DHA. A biocompatible organic solvent is added during the DHA production stage to extract the product. This process enables the production of high-quality lipid, thereby reducing extraction and purification costs. Eicosapentaenoic acid EPA Microalgae represent also 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. N. laevis could utilize glucose or glutamate as single substrate for heterotrophic growth, and the cellular EPA content of the alga in heterotrophic conditions was also higher than that in photoautotrophic conditions suggesting that this diatom is a good heterotrophic EPA producer. 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.

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TECHNOLOGICAL APPLICATIONS OF ALGAE In addition to previously mentioned importance of Algae, they have a lot of technological applications which include the following: Algae as research tools Algae are useful laboratory organisms because they are small, grow rapidly, have short generation times, and are easily cultivated under laboratory conditions. Cultures of many algal species are readily available from collections maintained by experts in several nations. Algae as biomonitors A bioassay is procedure that uses organisms and their responses to estimate the effects of physical and chemical agents in the environment. Biomonitors provide early warning of possible environmental deterioration, and may provide sensitive measures of pollution. One common use of algal cultures is as biomonitors in the detection, in natural or effluent waters, of algal nutrients or substances that are toxic to algae. While daphnids and fish have traditionally been the primary biomonitor organisms in aquatic ecosystems, algae are more sensitive than animals to some pollutants, including detergents, textile-manufacturing effluents, dyes and especially herbicides. Algal toxicity tests have become important components of aquatic safety assessments for chemicals and effluents. Use of fossil algae in Paleoecological assessments The silica skeleton of diatoms and silicoflagellates and decay-resistant cysts of dinoflagellates persist in ocean sediments for million of years, forming records used to deduce past environment changes. (Paleoecology (also spelt palaeoecology) uses data from fossils to reconstruct the ecosystems of the past). Microalgae in animal 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. Microalgae including Isochrysism Pavlova, Nannochloropsis, and various diatoms represent the primary food source for at least some stages in the life cycle of most cultivated marine animals. A major problem in cultivation is infestation with ciliates, amoebae, or flagellates, which can decimate the algal biomass within hours. Microalgal mass cultivation for production of food additives, hydrocarbons and other products A number of microalgae are cultivated for production of human "health-foods", or food additives such as β-carotene (which is converted to vitamin A during digestion) or protein extracts. In general, however, the high nucleic acid content of algae limit their use in human foods. Nucleic acids are converted to uric acid upon digestion. If consumed at a rate more than 50 grams per day, uric acid may precipitate as sodium urate crystals in joint cartilage, causing gout.

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The use of algae for removal of mineral nutrients in wastewater effluent Effluent treatment systems incorporate microalgal ponds or raceways, through which treated water is channeled, just prior to discharge. The algae remove inorganic nutrients and add oxygen. Algae in space research Algae have played a significant role in space research for several decades and will have future important applications in spacecrafts life-support systems, colonization of Moon and Mars, and eventually in terraformation (to make it habitable) of other planetary bodies. Experiments designed to study the growth of algae in zero-gravity conditions of space have flown aboard rockets, satellites, the space shuttle, and the Salyut and Mir space stations. Screening of algae for production of antiviral and antifungal compounds and other pharmaceuticals Various types of algae have proved to be sources of compound with antibiotic and anticancer activity, as well as pharmacologically useful products. The goal of screening programs is to survey cultivable organisms whose medicinal properties are unknown. Hydrophilic and lipophilic compounds of algae are initially screened for activity by testing their ability to reduce pathogenic effects on animal-cell cultures grown as monolayers in multi-well plates. For extracts showing activity, dilution studies are done to determine relative potency. Finally, efforts are made to identify the chemical structures of pharmacologically active compounds. Genetic Engineering of Algae for improved technological performance Just as crop plants are targets of genetic engineering efforts to improve productivity, broaden environmental tolerance limits, or increase pest or pathogen resistance, so too are useful algal species. DNA sequences are introduced into algal cells with goal of modifying biochemical pathways, either by changing expression of existing genes or by adding genes that yield a new different products. The ability to transform algal cells, i.e., to introduce and achieve desired levels of expression of foreign genes, has been made possible by a series of technical achievements. These include;

(1) identification of procedures that work best for incorporating foreign DNA into algal cells;

(2) development of promoter(1) systems for linkage to the genes of interest that will allow expression after the DNA has been incorporated into the host genome; and

(3) selection of an appropriate DNA marker (reporter gene)(2) that allows the genetic engineer to determine which cells have been transformed.

(1) A promoter is a region of DNA that initiates transcription of a particular gene. (2) A reporter gene (often simply reporter) is a gene that researchers attach to a regulatory

sequence of another gene of interest in bacteria, cell culture, animals or plants. Reporter genes are often used as an indication of whether a certain gene has been taken up by or expressed in the cell or organism population.

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