3. AGAR AND AGAROSE APPLICATIONS

The great bulk of agar produced worldwide is used in the food industry. Only 4–5% is used as bacteriological media. According to Santelices and Doty (1989) close to 5 000 tons of agar are processed annually from 25 000–30 000 tons of Gracilaria. Agar has that unique property of holding so much water in its gels (99.9%) so it is used widely for such gelling and stabilizer qualities not only in food but also in other industries.

3.1 Applications in the food industry

Agar finds its way as stabilizer in pie fillings, piping gels, meringues, icings, cookies, cream shells and other food products.

For icings the concentration of agar ranges from 0.2 to 0.5%. Agar stabilizes the icing and prevents the adhesion of the sugar coating to the wrapper. An improved stabilizer for icings is prepared by addition of 0.4 to 0.6% surface active agent to an agar level of 1.2 to 2.4% agar.

For doughnut glaze, 0.5 to 1.0% agar is used depending upon the amount of sugar needed. Agar increases the viscosity of the glaze, increases its adhesion to the doughnut, its quicker setting and flexibility and reduces chipping and cracking. Agar prevents the glaze from melting.

Agar is used as bulking agent in low calorie breads and at a concentration of 0.1 to 1.0% as antistaling agent in breads and cakes.

As an additive in jellied candies and confectionary specialties as marshmallows and sugared fruit slices, filler in candy bars and preparation of rigid gels agar is used in a concentration of 0.3 to 1.8%.

Agar gives smoothness to sherbets and ices in combination with other gums like locust bean gum at such combination of 0.12% agar, 0.07% LBG and 0.2% gelatin. Used at 0.05 to 0.85% in cream cheeses and yoghurt. Reduces wheying off and improves body and slicing qualities in cheeses.

Thickening and gelling agent in poultry, fish and meat canning at level of 0.5 to 2.0% in the broth weight. Helps preserve color in meat products.

For sausage processing agar keeps the moisture and prevents evaporation and drying up of the sausage and prevents weight loss and preserves the sausage, too. Make a 1.5% solution of agar by heating water to a boil then adding powdered agar and heat until the agar dissolves. Remove the agar solution from the heat while still warm and liquid and add 2.5 to 5 liters of agar sol to 50 kg sausage mass gradually kneading the mass while the agar sol is being added. The process should be done in strictly sanitary conditions.

Biscuits are usually coated with chocolate or other coatings to improve taste. To prevent the glaze or coating (flat icing) to break during packing or transport agar is added to the chocolate to give elasticity and better adherence. The chocolate is melted and the agar added, 35 ml of 1.5% agar solution for every 100 g of chocolate or 350 ml of warm agar solution to 1 kg of molten chocolate, stirred continuously until the mixture is well mixed and homogenized.

The following are some formulations and recipes for application of agar in foods:

Icing Stabilizers

Agar is used in the formulation of water-based, quick-set and slow-set bakery icings needed for wrapped and unwrapped baked goods. The flat or sweet-roll icings are prepared by boiling the agar stabilizer in a sucrose-water solution, then adding this hot mixture to the icing sugar. The icing is then applied hot at 50–60°C and the iced item can be wrapped as soon as 60 seconds later. Shorter or longer drying time for the icing can be regulated by increasing or decreasing the amount of agar in the following formulation:

A cake icing with a slightly slower setting time may be prepared by first dry-blending agar with salt, emulsifier, dextrose, starch and sucrose. This dry mix is metered into well-creamed Dex-Kreme (a Corn Products product); the entire mixture is heated to 48°C while mixing, and is then ready for application. The suggested basic formulation for the icing is:

Condensed Sweet Agar Jelly

Highly sweetened, mild-flavored candy of low-acidity, a modernized version of Yokan. This is usually wrapped in oblate. Agar is dissolved in boiling water to which sugar and invert sugar are added. The thick solution is cooked to 1C6°C for further evaporation. Cool briefly, then add the fruit juice and/or synthetic organic acid, flavors, color additives are added, mixed and allowed to gel overnight. The content of solids is about 70 to 75%. Further drying is done by placing the gel in a 55°C oven for 15–30 hours to reduce the moisture content to 16 to 18%. The gel is cut into small pieces and wrapped in oblate and then in cellophane. The ingredients are:

Oblate or Edible Paper

“Oblate” is a registered trade name for edible paper, or edible film, which is made from starch and agar. Its thickness is 10–15 μm. The product is generally sold as 93 mm diameter circles at drug stores in Japan.

Oblate is prepared by adding 100 parts of a 5% aqueous starch solution to 200 parts of 2.5% aqueous agar solution and brushing the hot mixed solution onto the glossy surface of a metal or glass in order to produce a dry, rigid film which is then removed and cut into the desired shape. It is a convenient and useful material for wrapping the condensed, sticky jelly and for doses of powdered medicines.

Yokan is the largest single application of agar in Japan. Fruits can be substituted for beans. Yokans are molded into ingot-shaped bars and packed and sealed in laminated film containers. The recipe is as follows:

Ref. T. Matsuhashi and T. Shimada. 1971. J. Jap. Soc. Food Sci. Technol. 18:360

Mitsumame is a sweet dessert especially popular among women (Japan). It is colorful and attractive and served in a glass bowl. It is prepared by soaking 1 cup of 1% agar gel cubes (1 cm² ) in syrup, together with pieces of sweetened mandarin, pineapple, cherries and peas (Pisum sativum var. arvense; mame means peas). Agar is able to keep the corners of the cubes which permits sterilization of the canned product. The agar gel used here has a high melting point (minimum, 85°C).

Mix the agar with water and stir continuously for about 20–30 minutes so the agar swells and moistens. Meantime, mix the pulp and the sugar, heat and then add the agar suspension. Mix the ingredients and boil for a few minutes with continuous stirring. Before pouring the mixture into the molds, add the appropriate flavor, color and preservative.

Fruit Jellies and Pastes

Suspend the agar in cold water, add the rest of the ingredients and boil for 10–15 minutes. Pour into molds.

Suspend the agar in cold water, mix the other ingredients thoroughly and boil 15–20 minutes. Pour into molds.

For jellies reduce the amount of agar by 50%.

Using the same quantities above, but substituting cooked chestnut puree, jellies with glazed chestnut flavor can be made.

Glucose can be used as substitute for the sugar. Jellies should be dried at room temperature. Jellies are covered with icing sugar to prevent them from adhering to the container or to one another.

Dissolve half the sugar in water before boiling, gradually add the agar and stir until the mixture boils. Add the remaining sugar until the agar is completely dissolved which will take from 7 to 10 minutes heating. Boil moderately and continue stirring. Pour the solution into molds or cylindrical tubes which can be cut to convenient sizes. The jellies are coated with icing sugar.

Mix the pulp thoroughly with the sugar, heat and boil over a water bath. Add the agar which has been dissolved in water and continue heating for 3–4 minutes with continuous stirring. Pour into molds.

Mix the agar with a small quantity of milk, add the rest of the ingredients then boil from 5–10 minutes. Beat after cooking.

Dissolve the agar in water, mix all the ingredients and filter while still warm. Allow to cool and beat.

The peach pulp can be prepared from fresh fruit or by straining the contents of a tin. Dissolve the agar in the syrup and mix it with the peach pulp. Allow to cool and beat.

A mix of the above ingredients is dissolved and boiled 5–10 minutes with half a liter of milk. For custards, use twice the quantity of milk.

Household Uses of Agar

Agar can be added to milk, coffee, fruit, wine, soda, etc. Add agar to the drink, heat and stir continuously until the mixture starts to boil. Turn off the heat and add a little sugar. Add more coffee, fruit, milk, wine, etc. according to taste. Mix well and pour into a mold and cool.

Prepare the same way as coffee jelly just substituting fruit for the coffee.

Dissolve the agar in water and heat with stirring until dissolved. Remove from heat and allow to cool a little, then add soda water and then allow to cool.

Wine Table Jelly

The preparation is the same as soda water table jelly using 50 ml wine and 250 ml water.

Milk Table Jelly

Dissolve the agar in water and boil. Mix thoroughly 2 tbsp. milk powder, enough sugar to taste, half an egg. Add the warm agar solution and heat. Pour into molds and cool.

3.2 Applications as culture media

In microbiology or solid culture media agar is used at a concentration of 1 to 2%. It is possible to culture anaerobes in air-exposed broths because at low concentration agar prevents the entry of oxygen into the liquid media and the usual range used is 0.007 to 0.03% agar. A very important application of agar is in tissue culture. With the growing interest in tissue culture as a standard method of propagation of selected strains of orchids from the meristem to grow virus-free clones and other ornamental plants, vegetable, fruit crops and other agricultural products the demand for agar as culture media is becoming so competitive so that the price has gone up immensely. Some tissues which are being cultured can tolerate food grade agar which offsets slightly the high cost of crop propagation. Propagation from seed of some forest trees involves the long wait for the trees to bear fruit and seeds to mature but with tissue culture the young tissues are taken and grown on nutrient media which thus facilitates reforestation within a shorter period of time.

Of course agar has been known for more than a hundred years as culture media for the separation of bacterial cultures in bacteriology.

3.3 Agar in impression materials (Meer, 1980)

As impression materials agar is used in prosthetic dentistry, in tool making and in criminology for making accurate casts. The formulation for dental impression material is as follows:

The commercial agar dental impression material can be managed by changing the gel into a sol with heat. The material is placed in an impression tray in the sol state and impressed against the mouth tissues which is to be reproduced as a dental stone. The tray is held rigidly in place and water is circulated through the cooling tubes attached to the surface of the tray. When the impression material has gelled the tray is removed and the impression is prepared for the pouring of the dental stone.

The gelation temperature of agar is approximately 36–38°C, the temperature at which the gel changes to the sol is 60–70°C. Such property makes agar useful for such application.

3.4 Agar in medicine and pharmacy

Agar has been used as laxative for decades because when hydrated it provides smooth nonirritant bulk in the digestive tract. Such agar is in the form of flakes which absorb from 12–15 times its weight of fluids. Agar is used as an ingredient in the preparation of capsules and suppositories, in surgical lubricants, in the preparation of emulsions, as suspending agent for barium sulfate in radiology. Agar is also used as a disintegrating and excipient in tablets. Sulfated agar has antilipemic activity similar to heparin. It is believed to inhibit the aerobic oxidation of ascorbic acid,

3.5 Other applications of agar

Agar is used for clarifying beer, wine or Japanese “sake”. It finds applications in photographic stripping films and paper. It is used in solidified alcohol fuel, dyed coatings for paper, textiles and metals and in pressure sensitive tapes, as flash inhibitor in sulfurmining explosives, as an ingredient in cosmetic creams and lotions, as corrosion inhibitor for aluminum, for the action of nicotine as insecticide in plant sprays. Agar is mixed with shellac and wax for shoe and leather polishes. It is used as setting inhibitor for deep well cement. Also as an adhesive in gloss finishing in paper products, agar is quite useful.

3.6 Application of agarose

The modern application of agarose is in biotechnology which includes molecular biology and genetic engineering; plant and animal cell and tissue culture; cell separations; immobilization supports; metabolic product recovery and purifications; clinical diagnostics in immunology and controlled release reagent delivery systems (Renn, 1984).

In electrophoresis agarose when containing appropriate buffer is an excellent medium in the separation of proteins and nucleic acids and their derivatives by applying an electric potential to the gel medium. Such separations depend upon the differential rates of migration of charged particles toward the oppositely charged electrodes when an electric potential is applied. Separation by molecular size depends upon the ability of particles to migrate through pores of the gel matrix. The smaller the molecule, the faster is the movement through the gel matrix and this is termed as molecular sieving electrophoresis. Such gel electrophoresis is used in chemical laboratories to identify proteins, enzymes, some abnormalities in serum and plasma and in biological fluids. Agarose is necessary in genetic engineering techniques in the separation of the desired gene DNA fragments and in gene mapping. Phages, viruses and capsides can be separated in low concentrations of agarose (0.035%). Recovery of fragments from electrophoretic separations could be accomplished by using the low-gelling, low-melting temperature hydroxyethylagarose.

In immunology agarose is used in the detection and study of disease indicators or antigenic materials and their specific antibodies. Antibodies (immunoglobulines) are specific proteins formed by animal cells in response to definite antigenic stimulus. The antigen will combine with the antibody to neutralize the threat of the disease to the animal. Methods have been devised using agarose to detect this antigen-antibody complexes, which appear as a cloudy or white precipitin band such as radial immunodiffusion, immunoelectro-phoresis, electroimmunodiffusion, counterelectrophoresis and so many other methods.

In chromatography agarose beads are used in columns where molecular size separations can be effected especially for molecules greater than 250 000 daltons. The almost neutral agarose effects only minimal nonspecific binding to the medium and thus retaining the biological activity of the molecule which are being separated. In affinity chromatography the enzymes, antigen, antibody, coenzyme, substrate, etc. are bound chemically or physically to the agarose gel particles. These are then eluted by chaning the pH or ionic strength of the eluant or solvent used in the fractionation.

Agarose finds application in immobilized cells and enzymes which attach to the agarose films, beads or particles and can transform one chemical to another. A very popular use of immobilized cells and enzymes is in the conversion of starch and sugar into alcohol by the use of immobilized yeast cells. Agarose is gaining popularity in fine highly technological applications.