Kaleeswaran, V. and Judith Betsy, C.
Introduction
Agar, alginate and carrageenan are the phycocolloids which are extracted from various red and brown seaweeds. They are non-crystalline substance with very large molecules, which dissolves in water to give a thickened (viscous) solution. They are water-soluble carbohydrates used to thicken aqueous solutions, to form gels (jellies) of varying degrees of firmness, to form water-soluble films, and to stabilize certain products, such as ice-cream. These phycocolloids find its application in a wide range of industry.
Agar
Red seaweeds belonging to the families of Gracilariaceae, Gelidiellaceae and Gelidiaceae contain agar as the major cell wall component. Agar is extracted from Gelidiumsp, Gelidiellaacerosa, Gracilaria edulis, G.crassa, G.foliifera, G.verrucosa, Pterocladiaspand Ahenfeltia sp. Agar consists of chain of 9-B galactopyranoseunits linked in 1, 4 bonds with a sulphatedL-galactose.
Agar is widely used in different ways due to its gelling ability and unique properties of these gels. Most of the agar produced is mainly used for the food application and some amount is used in bacteriological and other biotechnological uses. USFDA has classified agar as “Generally Recognized As Safe”. Agar can withstand higher temperature so it is used in the baked goods industry, 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 but by reducing the quantity of water and adding some agar will reduce this problem.
Pharmaceutical uses of alginates– www.artmolds.com
Agar extracted from Gracilariachilensis are called as “sugar reactive”because the sugar (sucrose) increases the strength of the gel andcan be used in preparing fruit candies. It is also a popular component of jellies. A popular Japanese sweet dish is mitsumamewhich 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 over gelatin because of its higher melting temperature and gel strength.
Agar based jelly– www.snapguide.com
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 because agar is not readily digested which adds less calorific value to food. It is used in vegetarian foods as meat substitutes.
In canned products of fish and meat processing industry, agar is usedas a protective coating against the effect of metal containers and against shaking during transport of these products. Agar is also used as a clarifying agent in wines, beer and liquors. It is used as a laxative for chronical constipation and as drug vehicle in pharmaceutical industry and is usedin the manufacture of ion exchange resins as an ion exchanger. Agar serves as aconstituentof skin creams and ointments in cosmetic industry and is used as finishing and sizing agentsin paper and textile industries.
Agar gels supplemented with nutrients can be used as the growth substrate to obtain clones or copies of particular plants. Meristems which are 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. Purified bacteriological agar is used in bacteria testing.
Carrageenan
Carrageenan is obtained from various red seaweeds belonging to the families Gigartinaceae, SolieriaceaeandHypneaceaeand is a sulphatedgalactanpolymer. It differs from agar mainly in its higher sulphated fraction and higher ash content. The back bone of the carrageenan polymer consists of 1, 3 and 1, 4 linked D-galactopyranose units which vary in the degree and the location of sulphated esterification. Carrageenan can be separated into two fractions such as kappa carrageenan with branched polymer chain and iota carrageenan with linear polymer chain. Precipitation with potassium chloride separates kappa fraction which is soluble in hot water from iota fraction, soluble in cold water. Carrageenan is mainly extracted from Chondruscrispus, Gigartinastellata, Iridaeasp, Eucheumasp and Kappaphycussp.
Carrageenan is mainly used in dairy products.When Kappa carrageenan is added to cottage cheese and ice cream at 0.01-0.04%, it preventswhey separation. The cocoa in chocolate milk can be kept in suspension by addition of similar amounts of kappa; it builds a weak thixotropic gel that is stable as long as it is not shaken strongly.Lambda or a mixture can also improve liquid coffee whiteners by preventing the separation of fat. The small containers of ultra-high temperature sterilized milk found in the refrigerators of some hotels may have kappa added to prevent fat and protein separation.
In food industry, carrageenan is also used in the preparation of condiment products, syrups, whipped creams, ice disserts, cheese etc and is used in the clarification of beer, fruit juices and other beverages. It improves the quality of wheat flour in spaghetti and parotta making. Carrageenan producers found that by combining various carrageenans with locust bean gum, konjac flour and starch, they can provide a variety of melting and non-melting gels and gel textures to meet the requirements of most of their clients.
Conventional fruit jellies are based on pectin and a high sugar content to help set the jelly. But in a low- or non-calorie jelly the pectin is replaced with mixtures of kappa and iota carrageenan. Fruit drink mixes to be reconstituted in cold water contain sugar (or aspartame), acid and flavour. Addition of lambda carrageenan gives a pleasant mouth feel. Sorbet is a creamy alternative to ice cream with no fat; use of a mixed kappa and iota together with locust bean gum or pectin provides a smooth texture to the sorbet.
Low-oil or no-oil salad dressings use iota or kappa to help suspend herbs, etc., and to provide the mouth feel that is expected from a normal salad dressing. The low oil content of reduced-oil mayonnaise normally gives a thin product, rather like a hand lotion; additives are needed to thicken it and to stabilize the oil-in-water emulsion and a combination of carrageenan and xanthan gum is effective. In hampreparation, brine solution is used in pumping and dispersing carrageenan to this brine solution after the brine salts are addedis known to improve the product qualitysince the carrageenan binds free water and interacts with the protein and retains the soluble protein.
There is a growing consumer demand for pre-cooked poultry products such as chicken and turkey pieces. Poultry processors were concerned about the loss of water during cooking and the loss in texture and eating quality. This was improved by injecting brine containing salt, phosphate and carrageenan into the muscle of the meat since the carrageenan binds water in the muscle and improves texture and tenderness.
When fat or salt is reduced, meat and poultry can suffer loss of tenderness, juiciness and flavour. Low-fat products formulated with phosphates and carrageenan can help to restore the juiciness and tenderness. Kappa carrageenan can replace half the normal fat. Iota carrageenan can be mixed with fresh ground beef and when cooked it provides fat-like characteristics and moisture retention that make the product more acceptable.
Itis used as emulsifiers in cod liver oil and emulsions as granulation and binding agents to tablets, elixirs, cough syrups etc. It is used extensively in ulcer therapy and for diseases of blood vessels.It isused as stabilizer and thickening agents in toothpaste, skin ointments and solid air fresheners. Hot waterextracts of carrageenan is used inprinting designs with dye and act asfinishing and sizing agents. Carrageenan, also called “Painter Moss”has been usedin paint manufacturing as stabilizers for pigments. They are also good as film-forming agents.
Bacteriological agar– www.carlroth.com
Algin
Algin or alginic acid is a membranemucilage and a major constituent of all alginates. The various salts of alginicacid are termed ‘alginates’ (sodium alginate, calciumalginateetc). Algin is obtained from brown seaweed species such as Ecklonia,Macrocystis, Undariand Laminariafrom temperate areas and Turbinaria, Sargassum, Cystoseiraand Hormophysafrom the topical areas.
Alginis used as emulsifiers in watery emulsions with fats, oils and waxes and used as fillers in the manufacture of tablets, pillsand as base of any ointments. An alginate gauze is used as a blood stopping plaster. Alginate forms a jelly in the stomachand produces saturatedfeeling in stomach and are considered as slimming agent. Ammonium alginate wool isused as a filter for microorganisms for laminar flowhood.
In cosmetic, detergent and soap making industries, alginates serve as thickening and dispersing agents in theproduction of ointments, creams, liquid emulsions, lotions and tooth paste as well as an additive in hair dye and shampoos because of the ability ofalginates to form films. Alginates increase the consistency of shaving creams. Alginatesare used for making denture mouldingsand fixatives.
In food industry, alginates improve the baking properties and they are constituent of baking emulsions. They are used to make sugar glazings and imitation fruits. Jelly products are madewith water andinsoluble alginates (calcium alginates).In many countries alginates are suggested as a gelation agent in marmalades and jams. Alginates are widely used in dairyproducts such as cheese, creams, milkshake mixed in chocolates, puddings, coldprepared pudding powder, soft cheese and custards.Alginates are used as stabilizers in milk mixes and impart uniform viscosity and goodwhipping ability.In beverages, alginates act as clarifying agent for making wines andraw liquor of sugar and molasses and as foam stabilizers in beer.
Alginate film are used to extend the shelf life of meat and sausage products. Artificial casings with an alginate base have been developed for making small sausages particularly for vegetarians. Alginate gel is used for deep freezing of fish, meat and poultry products.
In ceramic and leather industries, addition of alginate stabilizes the pigment and glazing suspensions to ceramic, porcelain and Chinaware as well as leather goods. Alginates find extensive application in textile industry, particularly as a thickening agent for printing dyes and paints that prevents smudging and promote quick drying and evenness of prints.
Conclusion
As per the available reports, India has 896 species of seaweeds comprising 455 species of Rhodophyta, 228 species of Chlorophyta and 210 species of Phaeophyta and 3 species of Xanthophyta. If suitable culture methods are adapted, the production potential of seaweeds can be increased. Phycocolloids has found its place in food industry, beverage industry, cosmetics, drug, textiles industry etc. By providing suitable microcredit to fishermen or fisherwomen, the production of seaweeds can be enhanced which will directly benefit other industries thus improving the economy.
(The authors are working at Fisheries College and Research Institute, Thoothukudi. Views expressed are personal.)
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