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1. Introduction

Algin is a natural polysaccharide, a common constituent of cell wall in all species of the brown seaweeds (Phaeophyceae). It is extracted by alkaline solution.

Algin was discovered in 1881 by an English chemist, E. C. C. Standford, who obtained a viscous mucilage by extracting Laminaria stenophylla (Laminariaceae) with alkali. He called the product “algin”. He further found that, if a mineral acid was added, a gelatinous precipitate was obtained, which dried to a hard, horny substance. He identified this as a new acid which he named “alginic acid”. He then carried out extensive investigations on the properties and possible uses of his products. Later, he started manufacturing algin on a commercial scale in Scotland.

In 1927 Thornley set up a company to produce alginate in San Diego, U.S.A. which in 1929 was reorganized into the Kelco Company. Production in the United Kingdom was initiated by Alginate Industries Ltd. during the period 1934–1939. Recently the two largest companies, Kelco and Alginate Industries, were been acquired by Merk & Co. Ind. U.S.A. They now produce about 70% of the world's alginate. The next largest producer is Protan A/S of Norway, followed by companies in Japan and France.

In China, algin production was initiated in 1957 in Qingdao from Sargassum pallidum. From the late 1960's Laminaria japonica has been used for algin production in place of Sargassum, since Laminaria was cultivated on a large scale.

Until now the term “algin” is widely used in commerce, referring specifically to the soluble sodium alginate. In the broader sense, algin refers to all alginic compounds, the acid and its salts, including the insoluble alginic acid and polyvalent salts of alginates, and the soluble alginates including alkali metallic alginates, Mg-alginate and other soluble derivatives of alginic acid, such as propylene glycol alginate.

2. Alginophytes and algin production

The major part of commercial algin is produced from the species of Macrocystis, Laminaria, Ascophyllum, Eisenia, Nereocystis, Lessonia, etc. The main commercial sources of alginophyte are shown in Fig. 22 and the main countries using them are shown in Table 16.

Table 16. Main alginophytes and the countries using them
AlginophyteHarvesting locationCountry of algin production
Macrocystis pyriferaNorth AmericaU.S.A.
Merocystis leutkeanaNorth America 
Ascophyllum NodosumScotland, IrelandNorway
Laminaria digitataNorway, FranceFrance
Laminaria hyperboreaScotland, IrelandEngland
Laminaria saccharina  
Laminaria japonicaJapan, China, KoreaJapan, China
Lessonia sp.ChileJapan, U.S.A.
Ecklonia sp.Japan, Korea, South AfricaJapan
Alaria sp.JapanJapan
Durvillea sp.Chile, AustraliaEngland, U.S.A.

Table 17 indicates the estimated world production of dried alginophytes in 1980.

Fig. 22

Fig. 22 Distribution map of alginophytes

Table 17. World production of dried alginophytes (1980)
CountryAlginophyte (Tons)
Australia3,000 T
China (1979)275,000
Mexico (1977)10,000
The Philippines1,750
South Africa3,000

The annual production of alginates of various countries was estimated to be more than 20,000 tons in 1980 (Table 18).

By more recent estimates, the annual production of alginates amounts to about 30,000 tons including 6,000 tons in China.

Table 18. Estimated production of alginates in various countries (1980)

CountryProduction (Tons)

3. Chemistry of alginates

A. Seasonal variations in the content and viscosity of alginate

Fig. 23

Fig. 23 The seasonal variation in the content of alginate in Laminaria japonca

The content and viscosity of alginates in the brown seaweed varies with the seasons, usually the content increasing from little amount at young stage to the maximum at the mature stage, and its viscosity approximately changing parallel to the content. Fig. 23 illustrates the variation of the content of alginate in Laminaria japonica, and Fig. 24 shows that of the content and viscosity in Sargassum pallidium (Ji et al., 1962, 1963). The latter has been used for algin production in the initial stage and the former is being used now in China.

Fig. 24

Fig. 24 The seasonal variation in the content and viscosity in Sarrassum pallium

Alginic acid contents in some Norwegian brown seaweeds on dry basis are 22–30% for Ascophyllum nodosum, 25–44% for Laminaria digitata, 35–47% for Laminaria digitata stipes, and 17– 33% and 25–30% for the fronds and stipes of Laminaria hyperborea, respectively, the values varying with the seasons.

B. Structure of alginic acid

Since Stanford discovered the alginic acid in 1881, till 1955 through huge amount of research work on the chemical components by lots of scientists, it has been verified that alginic acid is a linear polymer composed of 1, 4-linked β-D-mannuronic acid residues. In 1955 Fischer found another component, α-L-guluronic acid in alginic acid in addition to D-mannuronic acid by paper chromatographic technique. He pointed out that M/G ratios vary with different species of brown seaweeds. Studies later showed that the chains of 1, 4-linked α-L-guluronic and β-D-mannuronic acid are stereochemically very different as a result of their difference at C-5. It was further demonstrated from X-ray studies on the fibers of polymannuronic acid and those from alginic acid rich in guluronic acid content that the spacings along the fiber axis of 10.35 Å for mannuronic polymer and 8.72 Å for guluronic polymer. Conformations of the uronic acid units in agreement with these spacings are Cl for the 1, 4-linked β-D-mannuronic acid units and lC for the 1, 4-linked α-L-guluronic acid units. M block is linked diequatorially at C-1 and C-4, it is a relatively straight polymer, like a flat ribbon, while the G block is formed from diaxial groups at both C-1 and C-4, so the resulting chain is buckled (Fig. 25).

C. M/G ratios

The ratios of mannuronic acid to guluronic acid (M/G) in alginic acid vary widely with the species of alginophytes.

In Sargassum spp. the M/G ratios usually are lower than those in Laminaria japonica, indicating the former is rich in guluronic acid, while the Laminaria is rich in mannuronic acid (Table 19).

Table 19. The M/G ratio of Na Alginates extracted from various species of brown seaweeds (Ji et al., 1984)

SpeciesData and place of CollectionYieldM/G ratio
Sargassum pallidum1978.v Qingdao10.41.26
S. miyabei1978.iv. Qingdao14.10.76
S. thunbergii1978.ix. Qingdao12.80.78
S. hemiphyllum1978, Spring, Guangdong Province23.01.06
S. tenerrimum1978, Guangshi Province19.11.53
S. henslowianum1978, Guangdong Province17.80.82
S. patens1978, Spring, Guangdong Province16.01.59
S. siliquastrum1978. Spring. Guangdong Province18.11.13
S. horneri1979.ii. Dalian11.50.64
S. maclurei1979.ii. Guangdong Province23.61.47
Turbinaria ornata1980.iii. Hainan island20.60.89
Laminaria japonicaCommercial Na alginate--2.26

The M/G ratio of alginate in algae also varies with the seasons. Tables 20a and b show that M/G ratio of alginate from the basal part of Laminaria japonica increases from March to June. Although the seasonal variation of the M/G ratio in the apical part of L. japonica is not distinct, alginate prepared from this part always exhibits lower values than alginate from the basal part (Ji et al., 1984.).

The yield of alginate in both parts seems to give an increase tendency.

Table 20a. Seasonal variation of the yield and the M/G ratio in the Na alginate extracted from the basal part of L. japonica.

Date of collectionYield (%)M/G ratio
iv. 1413.82.96

Table 20b Seasonal variation in of the yield and the M/G ratio in the Na alginate extracted from the apical part of L. japonica.

Date of collectionYield (%)M/G ratio
iv. 1420.51.68

Table 21 and Table 22 indicate the seasonal variation of M/G ratios in alginates from Sargassum miyabe and Undaria pinnatifida, exhibiting a pattern similar to those from Laminaria japonica (Ji et al., 1984).

Table 21. Seasonal variation of the yield and the M/G ratio in the Na alginate of Sargassum miyabei

Date of collectionYield (%)M/G ratio

Table 22. Seasonal variation of the yield and the M/G ratio in the Na alginate of Undaria prinnatifida

Date of collectionYield (%)M/G ratio
Fig. 25

Fig. 25 Parts of alginic acid molecule

Table 23 shows the M/G ratios in alginates from European and American alginophytes.

Table 23. M/G ratio in alginate from European and American alginophytes

AlginophyteM/G ratio
Ascophyllum nodosum1.56, 1.29, 1.82, 1.0, 1.5, 1.85
Laminaria digitata1.45, 1.63, 1.16, 1.58
Laminaria hyperborea (fronds)0.62, 1.35, 1.28
Laminaria hyperborea (stipes)0.65, 0.40, 0.43, 0.37, 0.46
Macrocystis pyrifera (fronds)1.56

The stipe of Laminaria hyperborea is the most abundant source of alginate that is rich in guluronic acid. M/G 0.37 means the alginate contains 72% of guluronic acid. The Alginate Industries Inc. in U.K. specially produces such product, with the tradename ‘Manucol SS/LD/2’ (M/G 0.41), from the stipes of this species for special applications.

4. Properties of alginate

A. Solubility

The water-soluble salts of alginic acid include those of alkali metal (Na+, K+, etc.), ammonia and low molecular weight amines and quaternary ammonium compounds.

Alginic acid and the salts with polyvalent metal salts are insoluble. But magnesium alginate is soluble.

Alginates are soluble in water-miscible solvents such as alcohols and ketones. Alginate solution can be prepared in hot or cold. Sodium alginate is difficult to dissolve in hard water and milk because both contain Ca2+, which must be sequestered with a complexing agent such as sodium hexametaphosphate or EDTA prior to the addition of Na-alginate to it. An alginate solution can be easily prepared without forming clumps by first wetting the algin with small amount of alcohol or glycerol before adding the water to it. Propylene glycol alginate (80–85% esterified) is less affected by calcium ions and can be used in milk. When the pH of a medium is less than 4.0, PGA remains soluble down to about pH 2.

B. Viscosity and molecular weight

Sodium alginate or PGA solution gives a high viscosity when dissolved in water. Its viscosity increases with the concentration of alginate used and decreases with increasing temperature. The high-viscosity alginates are more apparent than the low-viscosity ones (Fig.-26). Increasing the limited amounts of polyvalent metal ion raises the viscosity and shortens the flow properties. Sodium alginate solution decreases in apparent viscosity with increasing shear rate. Low molecular weight alginate exhibits the Newtonian behavior. At low levels of calcium ion, the effect of calcium increasing viscosity is particularly apparent in the case of apparent in the case of alginates with higher content of D-mannuronic acid.

Fig. 26

Fig.26 Viscosity / concentration curves for various types and grades of alginates (25°C, Brookfield viscometer at 60 rpm).

The average molecular weight of alginate measured with viscosity and osmosis by using the equations:

and [η] = K.Mν, ranges between 48,000 and

186,000, and measured with ultracentrifugation ranges between 46,000 and 370,000.

The average molecular weight measured by viscometric method of some Chinese Sargassum alginates are summarized in Table 24 (Ji et al., 1982).

Table 24. Average molecular weight of Chinese Sargassum alginates

Sargassum pallidum9320,000
Sargassum hemiphyllum18339,500
Sargassum henslowianum11625,100
Sargassum paten18640,000
Sargassum siliquastrum10422,600
Laminaria japonica30265,100

DP: Average degree of polymerization,
MW: Average molecular weight.

C. Stability

Dried alginates, like other natural polysaccharides, are quite unstable to heat, oxygen, metallic ions, etc. In such circumstances alginates will be naturally degraded. During storage of the alginophyte the alginate contained in thalli degrades rapidly in the presence of oxygen, especially with an increase in moisture content. The high-viscosity alginate is more rapidly degraded than the medium- or low-viscosity alginate. The stability order of the alginates in storage is: sodium alginate > ammonium alginate > alginic acid, the last being the most unstable product.

Industrial grade alginate solution is easily degraded by microorganisms in the air, because such samples contain lots of algal particles and nitrogenous matter. The pure sodium alginate solution can be kept at room temperature for several months without distinct change in viscosity. All alginate solutions will depolymerize with increasing temperature. Alginate solutions are stable in the pH range 5.5 – 10 at room temperature for a long time, but will form the gel below pH 5.5. A limited amount of calcium ions may increase the stability of sodium alginate solutions. Propylene glycol alginate solution is relatively stable at room temperature at pH 3–4, but it will lose the viscosity rapidly below pH 2 and above pH 6.

Fig. 27

Fig.27 Schematic model for gel formation in alginates

: homopolymeric blocks of L- guluronate residues

D. Gelation

As mentioned above, polyguluronic acid chain are burckled, while polymannuronic acid chains are flat ribbons. This explains the difference observed in Ca2+ binding between the two. Controlled addition of Ca2+ to polyguluronic acid brings about gelation as the Ca2+ fits into the ‘egg boxes’ formed between the monomer units (Fig. 27). The calcium ions can coordinate with carboxyl groups and ring oxygen atoms in each of two parallel blocks. An alginate gel is formed as a three dimensional network of long chain molecules combined together by junction zones which are formed from G-block sections of the molecules and calcium ions. Strontium ions have an even better fit in the cavities and will be retained in preference if there is competition between Ca2+ and Sr2+. Hence, G-rich alginate has been verified to be an effective inhibitor for the removal of radioactive strontium from the gastrointestinal tract of a patient who is contaminated by it.

In the plant, the alginate is in equilibrium with seawater and is combined principally with calcium, magnesium and sodium, and it is supposed to be in the form of a gel with the calcium ions being concentrated in G-blocks, largely in junction zones, the other ions being associated with other parts of the alginate molecules. The flat ribbon M chains form more shallow ‘nests’, but also bind Ca2+. It might be expected at high cation concentrations.

In terms of structural differences, the gel of M-block exhibits elastic properties, that of G-block rigid properties. These properties are used in various applications of alginates.

E. Ion-exchange

The insoluble metal alginates behave as typical ion exchange resins. The affinities of divalent metal ions are dependent on the relative amounts of D-mannuronic acid and L-guluronic acid units in the alginate. The affinity of alginates for divalent ions decreases in the following order

  1. For the alginate rich in M from Laminaria digitata:
    Pb > Cu > Cd > Ba > Sr > Ca > Co, Ni, Zn, Mn > Mg,

  2. For the alginate rich in G from Laminaria hyperborea:
    Pb > Cu > Ba > Sr > Cd > Ca > Co, Ni, Zn, Mn > Mg.

The concentration of divalent cations required to bring about gel formation and precipitation for sodium alginate from two type seaweeds is the same, and increases in the order:

Ba < Pb < Cu < Sr < Cd < Ca < Zn < Ni < Co < Mn, Fe < Mg.

Aside from the interaction of metal ions with carboxyl groups of alginate, the hydroxyl groups on the polymer also play some role in ion binding.

5. Manufacture of alginates

Alginic acid in brown seaweeds is mainly present as calcium, magnesium and sodium salts. The first step in the manufacture of alginate is to convert the insoluble calcium and magnesium alginate into soluble sodium alginate by ion exchange under alkaline condition.

M: polyvalent cations such as Ca2+, Mg2+, etc.
Alg: alginate radical.

In order to facilitate the ion exchange process it is better to treat the alginophyte with dilute mineral acid before alkali extraction.

The crude sodium alginate solution extracted is filtered and precipitated with Ca2+ to form the insoluble calcium salt. The latter, on separation is converted to insoluble alginic acid by acidification for the removal of calcium ions.

2NaAlg + Ca2+ → Ca (Alg)2 + 2Na+

Ca(Alg)2 + 2H+ → 2HAlg + Ca2+

Then the alginic acid gels, after dehydration, are mixed with alkali (Na2CO3) powder to convert to soluble sodium salt again.

HAlg + Na+ → NaAlg.

Finally the sodium alginate pastes formed are dried and milled to sodium alginate powder.

A. Calcification process

Fig. 28 shows the plant flow sheet diagram of the manufacture of sodium alginate by calcification process.

Fig. 28

Fig. 28 The manufacture of sodium alginate by calcification process

Pretreatment: The alginophytes (Laminaria sp.) are treated, first, with 0.1 – 0.4% commercial formalin solution at room temperature for several hours to fix the pigments together with the phenolic substances present in the thalli diminishing the coloration of the extracted liquor. Then the thalli are soaked with dilute acid such as 0.1 M H2SO4 or HCl solution for 30 minutes at room temperature to convert the metallic salts of alginate into alginic acid.

Hot extraction: The treated wet thalli are extracted with 1% sodium carbonate solution at about 50 – 60°C for Laminaria and about 75°C for Sargassum for 1 – 2 hours in a steam-jacketed cooker equipped with a stirrer. The concentration of alginate in extracted liquor is about 1%, being too viscous to filter, so it should be diluted with 4 – 6 times volume of water to 0.2 – 0.3 % concentration (ca. 20–100 Cp.).

Filtration: Crude filtration is done with a rotary filter fixed with the 30–40 mesh nylon screen.

Floatation: The air is forced into the crude filtrate in tanks, and the bubbles adhere to the fine particles of insoluble residues to form flocs, floating on the surface with the bubbles. After standing for several hours the clarified liquor beneath it is drawn off at the bottom of the tanks. For food grade alginate it should be further purified by fine filtration.

Fine filtration: The clarified liquor is filtered with rotary nylon screen (100–120 mesh) filter or with the Dorr-Oliver rotary filter, coated with filter aid to remove the dispersed small particles.

Calcification: The filtrate is calcified with calcium chloride solution to precipitate the calcium alginate.

Bleaching: The Ca-alginate gels formed are bleached with NaClO solution (effective chlorine 0.05–0.10%). Ca-alginate is more resistant to degradation than alginic acid.

Acidification: The bleached calcium alginate gels are treated with dilute sulfuric acid or hydrochloric acid solution (0.5 M) to convert Ca-alginate into alginic acid by a three-step counter current conversion.

Dehydration: After washing with water, the gels are sent to the hydraulic press or screw press to dewater the gels with the solids reaching at least 25%.

Incorporation: The alginic acid gels are incorporated with sodium carbonate powder in a mixer. The pastes formed are squeezed through a porous plate, and the extrusions are chopped into pellets.

Drying and milling: The pellets are conveyed into the drying chamber or a fluid-bed dryer with a vibrator to dry at 80°C, and then milled to sodium alginate powder (60 mesh).

B. Alginic acid process

Some makers apply the acidifying process without using the calcification (Fig. 29).

Fig. 29

Fig. 29 The manufacture of sodium alginate by alginic acid process

Acidification: After fine filtration the filtrate is acidified with dilute H2SO4 or HCl in a pipeline controlled with a pH meter at pH 1.5–2.0, and alginic acid gels are precipitated and float to the liquid surface by CO2 bubbles formed by neutralization of acid and the excess of alkaline extractant. The mixture is left to stand for 1 hr, allowing completion of reaction and floatation of alginic acid.

Filtration and dehydration: The alginic acid gels are filtered with nylon bags and dewatered by hydraulic press, basket centrifuge or screw press. The alginic acid gels contain about 20–25% solids.

Conversion tank: The gels are conveyed to a conversion tank in which the ethyl alcohol, sodium hydroxide (40%) and bleaching solution (NaClO) are added. The alginic acid is converted to sodium salt in alcohol, and at the same time is bleached. The used alcohol is removed by using basket-type centrifuge and pumped to the recovery facility.

Dryer and milling: The fibrous sodium alginate formed is sent into the drying chamber, equipped for the recovery of alcohol vapor. Then the dried products are ground to sodium alginate powder.

C. Preparation of propylene glycol alginate (PGA)

The ability of sodium alginate to form gels with acids and calcium salts is an advantage in certain applications, but it prevents the use of sodium alginate as a stabilizer and viscosity-controlling colloid in acidic solutions. In 1945 an algin derivative, propylene glycol alginate (PGA) was first produced on a commercial scale in the U.S.A.; this extended the range of usefulness of algin to acidic solutions. The reaction of preparing this derivative is shown in Fig. 30, and the plant flow sheet diagram of PGA manufacture in Fig. 31.

Fig. 30

Fig. 30 The reaction of propylene oxide with alginic acid to form prolylene glycol alginate (PGA)

Fig. 31

Fig. 31 The plant flow sheet diagram of PGA manufacture

Alginic acid: The alginic acid gels prepared as above are subjected to dehydration process, also as above. The moisture content of the gels should be controlled to 45–55%. The gels are pulverized with a hammer mill.

Esterification: The fibrous alginic acid gels are allowed to react with gaseous propylene oxide (mole ratio 1:3) in a pressure vessel at 45 – 60°C for 8 hrs, giving a product with about 80% esterification. An alternative is that the solid content in the alginic acid gels should be kept at 65–78% and the esterification reaction runs at 60–100°C for 2 – 3 hrs. The final product gives approx. 80% mole ester, pH 3.8–4.6. More recently, good esterification may be achieved even with a low neutralization (0.4%), the solids in alginic acid gels being as low as 20–34%. The reaction runs generally at 75–85°C for 2 hrs.

Drying and milling: Same as above.

D. Preparation of G-rich alginate

Some makers produce G-rich sodium alginates, which will be used for the particular pharmaceutical uses (see below).

Selection of alginophyte: From the M/G ratios of alginates in different algae listed in Table 18 and Table 22, it is clear that some species of brown algae such as Laminaria hyperborea stipes and Sargassum spp. are highly rich in guluronic acid. Thus, for production of G-rich alginate the starting material containing low M/G ratio alginate should be selected.

Fractionation: The alginate is partially hydrolyzed with dilute organic acid such as 1 M oxalic acid; part of the alginate is solubilized. The insoluble residue can be fractionated into a mannuronic-rich fraction (M-blocks) soluble at pH 2.85 and a guluronic-rich fraction (G-blocks) insoluble at this pH. The fraction solubilized by partial hydrolysis contains roughly equal amounts of M- and G-uronides (MG-blocks). For example, Ji et al (1981) using Haug's method from Laminaria japonica, after partial hydrolysis for 8 hrs, 10.7% of G-blocks (M/G=0.27), 26.8% of M-blocks (M/G=5.63), and 68.7% of MG-blocks (M/G=1.70) were separated. From Sargassum hemiphyllum under the same condition, 34.4% of G-blocks (M/G=0.14), 11.3% of M-blocks (M/G=13.2) and 68.3% of MG-blocks (M/G=1.80) were separated.

Epimerization: The M/G ratio of alginate may be altered by treating with ‘mannuronan C-5 epimerase’, an enzyme isolated from the soil bacterium, Azotobacter vinelandii, on a laboratory scale. After cultivation with this bacterium in the alginate solution in the presence of Ca2+, the mannuronic acid residues are converted into guluronic acid residues in the polymer chain by the enzyme, and the resulting alginate gives a stronger gel and lower M/G ratio than the original alginate used. Although this method has not been applied on an industrial scale, but it is of the practical significance.

6. Application of alginates

Nowadays the alginates are widely used in food, textile industries and other fields including paper coating, pharmaceuticals and welding rods. The estimated proportions of specific uses to the total demand for alginates are shown in Table 25.

Table 25. Principal uses of alginate
UseQuantity of demand for alginate (%)
Textile printing50
Paper coating6
Welding rods5

A. In food

Alginates are used in food products as the thickening, gelling, stabilizing, bodying, suspending and emulsifying agents, as summarized in Table 26.

Table 26. Food application of alginates
UseFunctionApprox. use level ( % )
Dairy products:  
Ice cream:As a stabilizer in ice cream. Algin maintains a smooth texture and creamy consistency and prevents formation of large ice crystals.0.1–0.5
Ice milk:A frozen dessert, as a stabilizer, Algin gives good dryness and stiffness and slow meltdown to soft-serve ice milk.0.2–0.5
Milk-shake mixes:Hard-frozen ice milk, as a stabilizer, Algin provides good secondary overrun and creamy, thick milk shakes.0.25–0.5
Sherbets and water ices:Sherbets are frozen desserts, stabilized with PGA, and have clean flavor, smooth texture, and good body without crumbliness or sugar syrup separation.0.3–0.5
Chocolate milk:Algin-carrageenan compositions are used as a suspending agent to suspend cocoa fiber and to give a smooth, uniform-viscosity chocolate milk product.≤ 0.25
Yogurt, sour cream and imitation dairy products:Algin used as a bodying agent for viscosity control 
Bakery products:  
Icings:Bakery icings, it gives a soft gel consistency and light body and smooth texture, as a bodying agent.0.1–0.5
Cake fillings and toppings:Algin gives the products with a tender body and smooth texture, as a stabilizer. Upon aging, the fillings and toppings retain their texture and do not become tough or rubbery.0.3–0.5
Bakery jellies:
A freeze-thaw stable, bakery jelly.
Liquid egg white meringues and dry meringue powders, containing PGA, gives good texture, and bleeding is reduced.
Glazes:Algin-sugar combinations resist sweeting and do not become brittle.0.3–0.5
Pie fillings:Algin prevents separation and cracking, the filling has a soft, smooth gel body. For neutral or acid-type chiffon pie fillings, and for lipid-based, aerated, gelling filling.0.3–0.5 0.7–1.5 1.25–6.0
Other products  
Dietetic foods:Algin has a caloric value of about 1.4 cal/g. As most applications require less than 1% of algin, so the number of calories contributed by algin to dietetic foods is very low.-
French dressings:PGA in French dressings gives uniform emulsion ability, body, and flow properties.≤ 0.5
Salad dressings:PGA gives soft, smooth-textured salad dressings, produces a desired gel body that resists cracking and oil separation.0.1–0.2
Dessert gels:Algin gels are clear and firm, and can be easily molded, nonmelting at room temp.0.4–1.0
Candy gels:Ca2+ and algin makes candy gels ranging from soft tender types to chewy bodied gels.0.1–0.7
Beer foam stabilization:PGA produces a stable, longer lived creamier foam.40–80ppm
Creaming:In canning foods containing sauce or gravy.0.3–0.8
Noncarbonated fruit-flavored drinks:PGA gives a smooth-tasting product with better flavor release, as a suspending agent.0.1–0.25

B. In pharmaceuticals and cosmetics (Table 27)

Table 27. Pharmaceutical and cosmetic application of alginates
UseFunctionApprox. use level (%)
Suspensions:In some systems such as those containing penicillin, sulfa drugs algin is used as suspension agent.0.25–2.0
Jellies:Algin is used in surgical lubricants and medicated jellies.-
Ointments:Algin imparts body and emulsion stability to ointments, for excellent spreading properties.0.5–1.0
Emulsions:PGA used in pharmaceutical emulsions.0.5–1.0
Tablet disintegrating agents:Alginic acid or Na-Ca-alginate added to tablets accelerates the rate of disintegration.0.5–5.0
Tablet binder:Algin added to the medicament either in the dry powder or as a solution.1 – 2
(for powder)
1 – 5
(for solution)
Liquid shampoo:Algin gives improved pouring and handling properties.0.5–1.5
Dental impression material:Algin-based dental impression materials are easy to use, and have a controlled setting time at room temperature, the gels are tough and elastic, and give excellent reproducibility.-
Molding compounds:Used in industrial, art and surgical molding compositions.10–15
Medical dressing:Ca-alginate fibers woven into gauze are useful as haemostatic wound dressings and may be absorbed by body fluids.-
Absorption inhibitor for toxic elements:G-rich algin is used to inhibit the absorption of radiostrontium or lead by gastrointestinal duct of the animal.-

C. Industrial applications (Table 28)

Table 28. Industrial applications of alginates
UseFunctionApprox. use level (%)
Paper industry:  
Surface sizing:To produce paper and paper board with improved surface smoothness and uniformity and controlled surface density.-
Coatings:Algin reduces and controls the penetration of the coating into the web of the paper or paperboard.0.5
Adhesives:Algin controls the penetration and stabilizes the viscosity of starch-and latex-type adhesives.0.1–0.2
Textile industrial uses:  
Printing:Algin gives sharp lines without bleeding, color yields are good, after printing the algin is easily remived with water. Sodium alginate is inert toward many reactive dyes.1.5–3.0
Other industrial uses:  
Latex creaming:NH4-alginate is used as creaming rods for rubber latex and other polymer latices, it causes rubber latex and to separate into a high-rubber-solids cream layer and a low-rubber-solids serum layer.≤ 0.1
Welding rods:The coatings are used to welding rods to act as a flux and to control the conditions in the intermediate vicinity of the weld, such as temperature or oxygen and hydrogen availability.0.4–1.2 for low hydrogen welding rods. 0.15–0.25 for acid and organic types
Paints:In water-based paints, algin is used to suspend the pigments and control the viscosity.0.05–0.15
Boiler feedwaterAlgin facilitates the formation of a soft sludge rather than a hard scale in boilers, and reduces foam.-
Ceramic refractories:Algin improves the wet strength and plasticity of ceramic bodies.-
Binders for fish and prawn feeds:Alginates are used as a binder in fish and prawn feeds. It can lower consumption by up to 40% and pollution of culture ponds is sharply reduced. 
Immobilized biocatalysts:Alginate gels especially formed as gel beads are the excellent medium for entrapping biocatalysts (cells or enzymes). The latter are mixed with Na-alginate solution (2–4%) and dropped into CaCl2 solution and Ca-alginate gels form. A number of processes using immobilized biocatalysts appeared for (a) the production of ethanol from starch, (b) beer brewing with immobilized yeast, (c) fermentation to produce butanol and isopropanol, (d) continuous production of yogurt, etc. 
Controlled release of chemicals:Another type of immobilization of materials having biological activity gel beads is used to control the rate of release of the herbicides into soil or water. 

RAS/90/002 (RAS/86/024)

Working Papers

NACA-SF/WP/87/1. Lovatelli, A. Status of scallop farming: A. review of techniques. 22 pp.

NACA-SF/WP/88/2. Lovatelli, A. Status of oyster culture in selected Asian countries. 96 pp.

NACA-SF/WP/88/3. Lovatelli, A. and P. B. Bueno, (eds). Seminar report on the status of oyster culture in China, Indonesia, Malaysia, Philippines and Thailand. 55 pp.

NACA-SF/WP/88/4. Lovatelli, A. Status of mollusc culture in selected Asian countries. 75 pp.

NACA-SF/WP/88/5. Lovatelli, A. and P. B. Bueno, (eds). Seminar report on the status of seaweed culture in China, India, Indonesia, ROKorea, Malaysia, Philippines and Thailand. 79 pp.

NACA-SF/WP/88/6. Lovatelli, A. and P. B. Bueno, (eds). Seminar report on the status of finfish culture in China, DPRKorea, Indonesia, ROKorea, Malaysia and Singapore. 53 pp.

NACA-SF/WP/88/7. Lovatelli, A. Seafarming production statistics from China, Indonesia, ROKorea, Philippines, Singapore and Thailand. 37 pp.

NACA-SF/WP/88/8. Lovatelli, A. Site selection for mollusc culture. 25 pp.

NACA-SF/WP/88/9. Lovatelli, A. and P. B. Bueno, (eds). Seminar report on the status of finfish netcage culture in China, DPRKorea, Indonesia, ROKorea, Malaysia, Philippines, Singapore and Thailand. 56 pp.

NACA-SF/WP/88/10. Chong, K. C. Economic and social considerations for aquaculture site selection: an Asian perspective. 17 pp.

NACA-SF/WP/89/11. Chen J. X. and A. Lovatelli. Laminaria cultu re- Site selection criteria and guidelines. 30 pp.

NACA-SF/WP/89/12. Chen J. X. Gracilaria culture in China. 18 pp.

NACA-SF/WP/89/13. Seafarming Project, RAS/86/024. Site selection criteria for marine finfish netcage culture in Asia. 21 pp.

NACA-SF/WP/89/14. Lovatelli A. Seafarming production statistics from China, India, Indonesia, ROKorea, Philippines, Singapore and Thailand. 47 pp.

NACA-SF/WP/89/15. Chong K. C. and D. B. S. Sehara. Women in aquaculture research and training. 20 pp.

Working Papers

SF/WP/90/1. Chen J. X. Brief introduction to mariculture of five selected species in China. 32 pp.


NACA-SF/BIB/88/1. Selected bibliography on seafarming species and production systems. 20 pp.

NACA-SF/BIB/88/2. Selected bibliography on seafarming species and production systems. 52 pp.

NACA-SF/BIB/89/1. Selected bibliography on seafarming species and production systems. 49 pp.

Training Manuals

Manual on seaweed farming: Eucheuma spp. (Training manual No. 1). 25 pp.

Culture of the Pacific oyster (Crassostrea gigas) in the Republic of Korea. (Training manual No. 2). 64 pp.

Culture of the seabass (Lates calcarifer) in Thailand. Training manual No. 3. 90 pp.

Training manual on marine finfish netcage culture in Singapore. (Training manual No. 4). 275 pp.

Culture of Kelp (Laminaria japonica) in China. (Training manual No. 5). 204 pp.

Meeting Reports

Report of the First National Coordinators' Meeting of the Regional Seafarming Development and Demonstration Project, 27–30 October 1987, Bangkok, Thailand. 71 pp.

Report of the Second National Coordinators' Meeting of the Regional Seafarming Development and Demonstration Project, 20–23 September 1988, Singapore. 102 pp.

Report of the Third National Coordinators' Meeting of the Regional Seafarming Development and Demonstration Project, 24–27 August 1989, Qingdao, China. 103 pp.

Workshop Reports

Report of the FAO Asian Regional Workshop on Geographical Information Systems: Applications in Aquaculture, 5–23 December 1988, Bangkok, Thailand. FAO Fisheries Report No. 414, FIRI/R414. 13 pp.

Report of the Workshop and Study Tour On Mollusc Sanitation and Marketing, 15–28 September 1989, France. FAO/UNDP Regional Seafarming Development and Demonstration Project RAS/86/024. 212 pp.

General Reports

Progress report on the 1988 Regional Training/Demonstration Courses organized under the Regional Seafarming Development and Demonstration Project (RAS/86/024). 26 pp.

Report of the Seafarming Resources Atlas Mission. Regional Seafarming Project RAS/86/024, July 1989. 74 pp.

Audio-visual Materials

Culture of the Pacific Oyster (Crassostrea gigas) in the Republic of Korea. 71 slides.

Culture of the seabass (Lates calcarifer) in Thailand. 40 slides.

Marine finfish netcage culture in Singapore. 37 slides.

Culture of Kelp (Laminaria japonica) in China. 30 minutes video.

Seafarming Atlas Series

Regional Seafarming Resources Atlas. FAO/UNDP Regional Seafarming Development and Demonstration Project (RAS/86/024), January 1990. (Atlas series No. 1). 83 pp.


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