3. AGAR

3.1 Agar production methods

3.1.1 Food grade agar

A short and simplified description of the extraction of agar from seaweeds is that the seaweed is washed to remove foreign matter and then heated with water for several hours. The agar dissolves in the water and the mixture is filtered to remove the residual seaweed. The hot filtrate is cooled and forms a gel (jelly) which contains about 1 percent agar. The gel is broken into pieces, and sometimes washed to remove soluble salts, and, if necessary, it can be treated with bleach to reduce the colour. Then the water is removed from the gel, either by a freeze-thaw process or by squeezing it out using pressure. After this treatment, the remaining water is removed by drying in a hot-air oven. The product is then milled to a suitable and uniform particle size.

However, for a better understanding of the process, some of the details and difficulties need to be described.

There are some differences in the treatment of the seaweed prior to extraction, depending on the genus used. Gelidium is simply washed to remove sand, salts, shells and other foreign matter and is then placed in tanks for extraction with hot water. Gracilaria is also washed, but it must be treated with alkali before extraction; this alkaline pre-treatment causes a chemical change in the agar from Gracilaria, resulting in an agar with an increased gel strength. Without this alkaline pre-treatment, most Gracilaria species yield an agar with a gel strength that is too low for commercial use. For the alkali treatment, the seaweed is heated in 2-5 percent sodium hydroxide at 85-90°C for 1 hour; the strength of the alkali varies with the species and is determined by testing on a small scale. After removal of the alkali, the seaweed is washed with water, and sometimes with very weak acid to neutralize any residual alkali.

For the hot-water extraction, Gelidium is more resistant and extraction under pressure (105-110°C for 2-4 hours) is faster and gives higher yields. Gracilaria is usually treated with water at 95-100°C for 2-4 hours. The remainder of the process is the same for both types of raw material. The hot extract is given a coarse filtration to remove the seaweed residue, filter aid is added and the extract is pumped through a filter press equipped with a fine filter cloth. The extract is thick and will gel if allowed to cool, so it must be kept hot during the filtration processes.

The filtrate is now cooled to form a gel, which is broken into pieces (Figures 7 and 8). This gel contains about 1 percent agar. The remaining 99 percent is water that may contain salts, colouring matter and soluble carbohydrates. The gel may be treated with bleach to reduce any colour, washed to remove the bleach, and allowed to soak in water so that most of the salts can be removed by osmosis. The wash waters are drained and the remainder of the process is concerned with the removal of the 99 percent water in the gel. Either of two methods can be used for this.

The original method of water removal is the freeze-thaw process. The gel is slowly frozen so that large ice crystals form. The structure of the gel is broken down by the freezing so that when the material is thawed most of the water drains away, leaving a concentrated gel that now contains about 10-12 percent agar (this means about 90 percent of the original water content has been removed, and with it went a high proportion of any salts, soluble carbohydrates and soluble proteins that may have been present in the gel). Sometimes this gel is placed between porous filter cloths and squeezed in a hydraulic press to remove more water. However, this is a slow process, and usually the thawed material is simply drained and placed in a hot-air dryer. After drying it is milled to the required particle size, usually about 80-100 mesh size. Because of the refrigeration costs, this freeze-thaw process is relatively expensive, compared to the alternative described next.

FIGURE 7
Hot agar solution is fed, from the T-shaped PVC pipe, as a thin layer onto a stainless steel belt where it is cooled and forms a gel.

FIGURE 8
Pieces of gel breaking up as they fall off the end of the stainless steel cooling belt. A cutting device, consisting of a stainless steel screw and thin wire, is at the bottom of the ramp.

Sometimes the thawing is accelerated by washing the frozen blocks of gel with large quantities of water (Figure 9), but this adds to the already large water consumption of the process.

The alternative process relies on synaeresis. This is the term used to describe the separation of liquid from a gel. A common example is that of a partly used jar of jam or preserves that is left standing for several days: pools of liquid can often be seen at the surface. However, for the agar gel, pressure is used to force the separation of the liquid. The equipment used is based on the following. Two grooved metal plates are covered with porous cloth and the 1 percent agar gel is placed between the cloths, like a sandwich with metal plates on the outside, then the layers of cloth, with the gel in the middle. Pressure is applied to the metal plates and very slowly increased over about 24 hours, forcing liquid out of the gel, through the cloths, down the grooves of the metal plate and away to a drain. The piece of equipment contains about fifty of these sandwich-type units, all in a vertical plane, all being placed under pressure by one hydraulic ram (Figure 10). At the end of the time, the pressure is released, the metal plates are separated and the remaining gel, now containing about 20 percent agar, is peeled off the porous cloth (Figure 11). It is shredded and dried in a hot-air oven before being milled to the required particle size, usually about 80-100 mesh size. With no refrigeration required, the energy consumption is obviously much lower than for the freeze-thaw method, and, since more water has been removed, less soluble matter remains, so the agar is more pure. Less energy is also needed in the drying process since less water is being removed. This process based on synaeresis has been widely adopted by large agar producers who can afford the higher capital costs for this equipment.

FIGURE 9
Thawing frozen slabs of agar by hosing with water.

FIGURE 10
Dewatering machine used to squeeze water from agar gel.

FIGURE 11
A sheet of agar gel after squeezing in the dewatering machine.

FIGURE 12
Agar blocks (left) and agar strips (right).

FIGURE 13
Flow chart for the production of agar (after Armisen and Galatas, 1987).

Figure 13 summarizes the production processes for agar.

A large and reliable freshwater supply is a requirement for an agar factory. Water consumption is high and the processing of Gracilaria requires more than for Gelidium. Higher water consumption also means larger quantities for waste disposal, so recycling of water is becoming more necessary, depending on the location of the factory.

For further details

Detailed information on the commercial extraction process is not easily available. There are several short publications on the results from laboratory-scale extractions, but commercial agar producers are generally secretive about the details of their processes. Armisen and Galatas (1987) is one of the few publications that gives some details, but there are still many gaps, particularly in the conditions of the alkali treatment and the subsequent hot water extraction; nevertheless, it is the best starting point. The original print version may not be readily available but it can be read and downloaded from the FAO Web site (see References 2 - Internet sources). A later book chapter by the same authors, Armisen and Galatas (2000) gives a useful comparison of the freeze-thaw and synaeresis methods for removing water from the agar gel. Nussinovitch (1997: 4-5) also has a few useful details about extraction.

3.1.2 Agar strips

Agar for use in food is sold in two forms: strip agar and agar powder. The powder is produced by the method previously described. Agar strip, sometimes called natural agar, is produced on a small scale in China, Japan and the Republic of Korea by the old, traditional method. Gelidium must be used; it was the only raw material used before the Second World War. It is boiled for several hours in water, acidified by the addition of either vinegar or dilute mineral acid. The hot extract is filtered through cotton cloth, then poured into wooden trays to cool and form a gel. The gel is extruded to produce spaghetti-type strips about 30 cm long. The strips are placed outside at night to freeze and allowed to thaw in the day, so water is released and runs off, leaving a more concentrated gel. This process can be repeated, or modern refrigeration can be substituted. The strips are dried in the sun, which also bleaches the strips. Strips are assembled into bundles and sold for domestic use (Figure 12). Prior soaking makes them easier to dissolve in boiling water.

3.1.3 Bacteriological agar

This can only be made from species of Gelidium because the resulting agar has a low gelling temperature (34-36°C) that allows the addition of other materials to the agar with a minimum risk of heat damage. Gracilaria and Gelidiella give agars that gel at 41°C or higher. "Bacto" agars must not contain anything that might inhibit the growth of bacteria, such as trace metals, soluble carbohydrates or proteins, nor should they contain any bacterial spores. They must not interact with any materials that must be added as nutrients for the bacteria under study. The gels must be strong and have good clarity. Manufacturers of bacteriological agar keep all processing details confidential. However, recently Kim et al. (2000) published details [in Korean] of a pilot-scale preparation that they claim gave a product that is superior to commercial bacteriological agar. Armisen and Galatas (1987) and Armisen (1997) discuss the necessary specifications for bacteriological agar.

3.1.4 Agarose

Agar can be divided into two principal components: agarose and agaropectin. Agarose is the gelling component; agaropectin has only a low gelling ability. There are several methods of producing agarose; many rely on removing the agaropectin from the agar. There are only a small number of processors who produce purified, high quality agarose for a small but growing market, mainly in biotechnology applications. These processors use good quality agar as their starting material rather than seaweed, and are often not in the seaweed processing business. Armisen and Galatas (1987) summarize the methods that have been used to isolate agarose from agar, and discuss the specifications expected for a high quality agarose.

3.2 Agar producers

A summary of the capacity of agar producers according to their broad geographical location is given in Table 2.

TABLE 2
Agar processors. Capacity in tonnes (2001)

Source: H. Porse, CP Kelco ApS, 2002, pers. comm.

The principal agar producers are listed below.

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Spain
Hispanagar, S.A.
Avenida López Bravo, 98
Polígono de Villalonquejar
Apartado Postal 392
08080 Burgos
Tel: [INT+34] + 947 298 519
Fax: [INT+34] +947 298 518
Website: www.hispanagar.net
This is the largest Spanish phycocolloid factory, which produces food and bacterio-logical grade agars, Purified Bacteriological Agars (for use with specially sensitive bacteria and in bacterial metabolism assays as well as in biochemistry). They also produce many different types of agarose for biochemistry and molecular biology, being the world's largest producer of agaroses.

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Industrias Roko, S.A.
Rua os Regos 27
Oleiros,
La Coruña 15173
Tel: [INT+34] +981 631 159
Situated near Oviedo, it produces food grade agar and some types of bacteriological agar.

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Algas de Asturias, S.A.
LG Bria - Posadas de Llanes
Llanes - Asturias
A smaller factory that produces food grade agar and some types of bacteriological agar.

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Portugal
Iberagar S.A.
Estrada Nacional 10, Km. 18, Coina
Tel: [INT+35] +(121) 210 9252
Fax: [INT+35] + (121) 210 9255
Website: www.iberagar.com
Produces food and bacteriological grade agars.

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Morocco
SETEXAM, S.A
Km 7 Route de Tanger,
B.P. 210
14000, Kenitra
Tel: [INT+212] + 7 378 496
Fax: [INT+212] + 7 378 448
Marokagar, S.A.
44 Rue Abou Baker Wahrani
B.P. 2121
Casablanca 05
Tel: [INT+212] + 2 623 611
Fax: [INT+212] + 2 614 895

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Chile
Algas Marinas S.A. (Algamar)
Fidel Oteiza 1956 Piso 14
Providencia, Santiago
Tel: [INT+56] + (2) 205 5086
Fax: [INT+56] + (2) 205 5184

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Prodoctora de Agar S.A. (Proagar S.A.)
Av. Vicente Perez Rosales 800
Llanquihue
Tel: [INT+56] + (65) 242 635
Fax: [INT+56] + (65) 243 312
In 2000, this Japanese controlled company claimed to be the world's second-largest agar producer, exporting about 450 tonne/year.

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Agar del Pacifico S.A.
Av. Federico Schwager 1112 -
Parque Industriel Coronel
Coronel
Tel: (56-41) 75 1286
Fax: (56-41) 75 1143

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Cobra Chile S.A.
Av. Andres Bello 1051 Of. 2501
Providencia, Santiago
Tel: [INT+56] + (2) 236 1582
Fax: [INT+56] + (2) 236 0276

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Japan
Ina Food Industry Co., Ltd.
574 Tsurumakicho, Waseda
Shijuku
Tokyo 162
Tel: [INT+81] + (3) 3235 8861
Fax: [INT+81] + (3) 3235 8863

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Matsuki Agar-Agar Industrial Co., Ltd
2638 Miyagawa
Chino City
Nagano-Pref
Tel: [INT+81] + (266) 724 121

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The Republic of Korea
Myeong Shin Chemical Ind. Co., Ltd.
2191-3 Songbaek Sannae
Milyang, Kyeongnam
Tel: [INT+82] + (55) 352 0547
Fax: [INT+82] + (55) 352 0548
Website: www.miryangagaragar.com
(agar factory)

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Myeong Shin Chemical Ind. Co., Ltd.
439-13, Soju-Ri, Ungsang-Up,
Yangsan-gun, Kyeong-Nam,
Tel: [INT+82] + (55) 389 1001
Fax: [INT+82] + (55) 389 0478
(Head Office and carrageenan factory)

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Indonesia
P.T. Agarindo Bogatama
Jl. Gajah Mada No. 3
Komplex Duta Merlin Blok E No.34-35
Jakarta 10130

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For further details about Indonesia and other Indonesian companies contact the Indonesian Seaweed Industry Association (APBIRI)
Asosiasi Pengusaha Budidaya dan Industri Rumput Laut Indonesia (APBIRI)
BPPT Lt. 13
Jl. MH Thamrin No. 8
Jakarta Pusat 10340
Tel: [INT+62] + 21 322430

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Mexico
Agarmex S.A.
Ensenada

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New Zealand
Coast Biologicals Ltd
Factory Road
Opotiki
Tel: [INT+64] + 7 315 7663
Fax: [INT+64] + 7 315 8002
Produces only bacteriological agar from Pterocladia.

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France
SOBIGEL S. A.
Rue de L'industrie B.P. 304
64703 Hendaye
Tel: [INT+33] + (55) 9201844
Fax: [INT+33] + (55) 9202362
Owned by Hispanagar, S.A.

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Argentina
Soriano S.A.
9 de Julio 745
9100 Trelew
PCIA Chubut

3.3 Agar uses

The uses of agar centre around its ability to form gels, and the unique properties of these gels. Agar dissolves in boiling water and when cooled it forms a gel between 32° and 43°C, depending on the seaweed source of the agar. In contrast to gelatin gels, that melt around 37°C, agar gels do not melt until heated to 85°C or higher. In food applications, this means there is no requirement to keep them refrigerated in hot climates. At the same time, they have a mouth feel different from gelatin since they do not melt or dissolve in the mouth, as gelatin does. This large difference between the temperature at which a gel is formed and the temperature at which it melts is unusual, and unique to agar. Many of its applications take advantage of this difference.

For details on the chemistry of why and how agar forms gels see Nussinovitch (1997) or Armisen and Galatas (2000).

3.3.1 Food

About 90 percent of the agar produced is for food applications, the remaining 10 percent being for bacteriological and other biotechnology uses. Agar has been classified as GRAS (Generally Recognized As Safe) by the United States of America Food and Drug Administration, which has set maximum usage levels depending on the application. In the baked goods industry, the ability of agar gels to withstand high temperatures means agar can be used as a stabilizer and thickener in pie fillings, icings and meringues. Cakes, buns, etc., are often pre-packed in various kinds of modern wrapping materials and often stick to them, especially in hot weather; by reducing the quantity of water and adding some agar, a more stable, smoother, non-stick icing is obtained.

Some agars, especially those extracted from Gracilaria chilensis, can be used in confectionery with a very high sugar content, such as fruit candies. These agars are said to be "sugar reactive" because the sugar (sucrose) increases the strength of the gel. Because agar is tasteless, it does not interfere with the flavours of foodstuffs; this is in contrast to some of its competitive gums that require the addition of calcium or potassium salts to form gels. In Asian countries, it is a popular component of jellies; this has its origin in the early practice of boiling seaweed, straining it and adding flavours to the liquid before it cooled and formed a jelly. A popular Japanese sweet dish is mitsumame; this consists of cubes of agar gel containing fruit and added colours. It can be canned and sterilized without the cubes melting. Agar is also used in gelled meat and fish products, and is preferred to gelatin because of its higher melting temperature and gel strength.

In combination with other gums, agar has been used to stabilize sherbets and ices. It improves the texture of dairy products like cream cheese and yoghurt. It has been used to clarify wines, especially plum wine, which is difficult to clarify by traditional methods. Unlike starch, agar is not readily digested and so adds little calorific value to food. It is used in vegetarian foods such as meat substitutes.

3.3.2 Other uses

In the pharmaceutical industry agar has been used for many years as a smooth laxative.

In orchid nurseries, agar gels containing appropriate nutrients are used as the growth substrate to obtain clones or copies of particular plants. Meristems - the part of the plant with actively dividing cells, usually the stem tips - are grown in the gel until there has been sufficient root development and growth for them to be transplanted. An advantage of this system is that the plants can be cultured in a sterile environment.

3.3.3 Microbiological agar

Bacteriological agar is used in testing for the presence of bacteria. It is specially purified to ensure that it does not contain anything that might modify bacterial growth. It is therefore more expensive, frequently at least twice the price of food grade agar. A hot agar solution (1-1.5 percent) is prepared and as it cools, nutrients or other chemicals specific for the type of bacteria being tested are added. When the solution has cooled below its gel point, the sample suspected of containing bacteria is spread on the surface of the gel, which is then covered and stored at a temperature suitable for bacterial growth. The agar gel should be as clear as possible so that any bacterial growth can be easily seen.

For further details

Further information about the uses of agar can be found in Glicksman (1983) and Armisen and Galatas (1987, 2000). Armisen and Galatas (2000) also contains some interesting recipes for yokan (traditional Japanese), sweet potato dessert (traditional Argentinian) and sugar icings, all of which illustrate typical methods for using agar in foods. Armisen (1997) lists eleven important advantages enjoyed by agar in food applications. Armisen (1995) is a paper about the use and importance of Gracilaria, but it also has useful discussions about natural and industrial agars, compares the characteristics of agars from Gelidium and from Gracilaria, and is useful background reading for those wishing to learn more about the agarophyte and agar industries.

TABLE 3
Agar markets (2001)

NOTE: The total market has a value of about US$ 137

Source: H. Porse, CP Kelco ApS, 2002, pers. comm.

3.4 Markets and marketing of agar

A summary of the agar markets is shown in Table 3. It does not include production from Gelidiella acerosa and Gracilaria species in India, where 800-1 300 dry tonnes of seaweed are used to produce 100-160 tonnes/year of agar.

All the companies previously listed as agar producers sell directly to agar users. However, there are other companies that buy from producers and re-sell the agar, either alone or in admixture with other hydrocolloids, to users. These companies specialize in supplying food ingredients, usually defined as food additives that improve the quality, texture, stability or presentation of a food product. Because they are more active in the carrageenan and alginate industries, further discussion about them can be found later, in the relevant sections.

Some future prospects for the red seaweed industry and its hydrocolloid products are considered by Kapraun (1999).

3.5 Future prospects

The market for food grade agar is stable and not likely to expand very much in the near future, unless new uses are developed, and this does not seem likely at present. During the last 30-40 years agar has gradually been replaced in some of its traditional uses by other hydrocolloids that either gave a better result in particular applications or are cheaper. Uses now are restricted to those that depend on the unique gelling properties of agar. There are many producers, some endeavouring to capture market share with low price or low quality material, so it is becoming a very tight market. The bacteriological agar market is also stable, but present prospects are that it is unlikely to show much expansion in the next five years. The market for agarose will expand during the next five years as its uses in biotechnology increase and probably diversify as new techniques are developed. However, it is a specialized and relatively small market; users often purchase in lots of 100 g, with a total worldwide consumption of about 50 tonne/year.