PRODUCTION, PROPERTIES, AND USES OF ALGINATE, CARRAGEENAN AND AGAR

OLIVIER BARBAROUX

IFREMER
Departement Ressources Vivantes
Laboratoire d'Algologie Applique
Nantes cedex 01, France

Introduction

Carrageenans are commercially important hydrophilic colloids (water-soluble gums) which occur as matrix material in numerous species of red seaweeds (Rhodophyta) wherein they serve a structural function analogous to that of cellulose in land plants. Chemically they are highly sulfated galactans. Due to their half-eater sulfate moieties they are strongly anionic polymers. In this respect they differ from agar and alginate, the other two classes of commercially exploited seaweed hydrocolloids. Agar, though also galactans, have little half-ester sulfate and may be considered to be non-ionic for most practical purposes. Alginate, though anionic, are polymers of mannuronic and guluronic acids and as such owe their ionic character to carboxyl rather than sulfate groups. In this respect alginate are more akin to pectins, found in land plants, than to the other seaweed hydrocolloids.

PRODUCTION,
PROPERTIES
AND
USES
OF
ALIGATES

ALGINATES

Alginates* were first isolated by Stanford by alkalineextraction of brown algae a process used for iodine extraction. The use of the brown seaweeds is well-known since ancient times: Chinese people and Romans used themin medicines and cosmetic preparations. Production on an industrial basis started in the United-States around 1930. At the beginning,Alginates were used for the production of canned foods intended for seamen. * Algin is also the genenc term for salts of alginic acid
	BROWN ALGAE

STRUCTURE

	Alginic acid is a polyuronide made up of a sequence of two hexuronic acid residues:3-D-mannuronic acid unit and α-L-guluronic acid.

Alginic acid is a polyuronide made up of a sequence of two hexuronic acid residues: β-D-mannuronic acid unit and α-L-guluronic acid.

When examining the Haworth formula, it can be observed that the two acid residues involve epimerization at C-5. The only difference is the occurence of the linkage C-5 - C-6, above or below the medium plane of the ring. The bulkiness and the interactions, due to the acid function at C-6, dictate the conformation of the ring and involve the equatorial position of the acid function. The 3-D-mannuronic acid unit adopts always the C conformation and α-L-guluronic acid residue the C conformation.

The investigations by partial hydrolysis carried out by Haug and Larsen and more recently the studies by C NMR Spectra (Nuclear Magnetic Resonance Spectroscopy) show that these two monumer residues do not display a random distribution but occur in blocks containing about 20 units.

Macromolecules are associations of these blocks at various degrees depending on the species used and to a lesser degree the maturity of the seaweed and the area of harvesting. Infrared spectroscopy provides a rough but rapid information regarding the percentage of mannuronic acid residues and guluronic acid units.

The distribution of the monomer residues controls the alginate capacity to form gel. The guluronic blocks have the conformation best suited to the calcium-induced gelation.

Brown seaweeds are found along rocky coasts. They grow along the North atlantic coastline; mainly in the United-States, Great-Britain, France (Brittany) and Norway.

In France, brown seaweeds are harvested along the Brittany coasts. Alginates are essentially extracted from:

These seaweeds display large variations in mannuronic/guluronic proportions.

BOTANICAL SOURCE

ALGINATES

EXTRACTION PROCEDURE

All processing stages are based upon the two following properties:
alkaline metal alginates are soluble in water,
alginic acid and its calcium derivative have very limited solubility in water.

DEMINERALIZATION

The process consists of macerating seaweeds with diluted mineral acid, which allows ion exchange between the calcium of alginate and the hydrogen of the acid used. Thus the alginate contained in the algae is converted to alginic acid by systematic lixiviation, while non-desirable constituants (fucoidine mannitol, mineral salts…) are removed.

ALGINATE EXTRACTION

The demineralized seaweeds are then ground in the presence of an alkali or an alkaline salt which neutralizes alginic acid and converts it to the soluble alginate corresponding to the salt used. The insoluble matters (cellulosic and proteinic components) are removed by filtration, floatation and settling.

COLLOIDS COAGULATION

This is carried out by a mineral acid to the alginate solution. The alginic acid precipitate is then washed and dried.

NEUTRALIZATION e.g. PREPARATION OF THE DIFFERENT ALGINATES

Alginic acid is neutralized with different alkaline bases or basic components according to the type of alginates required. It occurs:

• by mixing the components or.
• by exchange in alcohol.

The final product is then dried, milled and sieved to the desired particle size.

Production of sodium alginate

Uses of Alginate

Thickener

• ices and ice creams
• products for pastries
• toothpastes
• cosmetics
• textile printing
• paper printing
• water flocculation

Gelling agent

In the presence of calcium and acid

• reformed or structured products
• entrapment and immobilization of enzymes and microorganisms
• absorbent products

PRODUCTION,
PROPERTIES
AND
USES
OF
CARRAGEENAN

CARRAGEENANS

Residents of County of Carra ghen on the south coast of Ireland used Irish moss in foods and medicines more than 600 years ago. These red seaweeds were used because of their unique property to gel milk.

In the meantime, these seaweeds were also collected along the French coastal areas and in particular in Brittany. The bleached “lichen” was used to prepare a milk-gel known as “blanc-mange”. It was obtained on cooling after cooking of the seaweeds in milk.

This use was also occuring in the United States. However, it was not until world war II that an industrial extract was produced in this country. At the beginning, only the “lichen”, a blend of Cnonarus crispus and Gigartina stenata was used. Lately the industry has been utilizing other red seaweeds sources.

STRUCTURE

Carrageenans are sulfated polymers made up of galactose units. Several fractions have been determined, but a common backbone can be defined. Carrageenan consists of a main chain of D-galactose residues linked alternately α - (1 → 3) and β - (1 → 4). The differences between the fractions are due to the number and to the position of the sulfate groups and to the possible presence of a 3.6 anhydro-bridge on the galactose linked through the 1 - and 4 -positions.

The proportion of the different fractions varies with the species of the seaweeds as well as with the habitat and the season of harvesting.

An informative way to determine the structural characteristics of carrageenans is to perform an infrared spectrum.

INDUCED GELATION with Kappa κ or lota ι CARRAGEENANS
and their biological precursors Mu (μ) and Nu (ν)

The main chain of κ- and ι -carrageenans contains β-D-galactose 4-sulfate linked through the 1- and 3- positions in the ⁴C₁ conformation and 3.6 anhydro-galactose linked through the 1- and 4- positions in the C₄ conformation. The only difference between ι- and κ-carrageenans comes from the 2-sulfatation of the 3.6 anhydro-galactose: the ι-carrageenan contains an additional sulfate group.

The macromolecules of the gelling carrageenans are not pure in κ or ι but are present as hybrids. There is always a small part of ι in κ fraction and vice versa. In addition. in the macromolecule. other units can be found. in particular μ (mu) and ν (nu) carrageenans.

The dimer unit of μ- or ν-carrageenans consists of galactose 4-sulfate linked through the 1- and 3- positions in ⁴C conformation and galactose 6-sulfate linked through the 1- and 4- positions in ⁴C₁ conformation. As ι and κ-carrageenans. the only difference between μ and ν precursors comes from an additional sulfate for ν-carrageenan.

The gelation of κ- and ι-carrageenans is induced by the association of chains through double helices. Only the repetitive sequences of ⁴C₁ and ¹C₄ conformations of the galactose units are able to form a double helix. In native carrageenans. the presence of μ- and ν-carrageenans interrupts the regularity of the chain and deviations (called “kinks” by Rees) occur. The regular sequences are then too small to create stable linkages and only weak gel can be produced.

To increase their gelling effect, carrageenans are extracted in an alkaline system. This process catalyses an elimination of 6-sulfate groups of μ- and ν-carrageenan units.

As it induces the 3.6 anhydro-galactose formation. μ- and ν- carrageenan units are transformed into κ- and ι- carrageenans. The chain becomes more regular and the gel strength is greatly increased.

In seaweeds. a specific enzyme induces the same transformation. For that reason μ- and ν- carrageenan are called “biological precursors” of κ- and ι- carrageenans.

CARRAGHÉNANE GÉLIFIANT

Le Kappa carraghénane est formé par un enchanement de
β - D- galactoses, 4-sulfate lié en 1 et 3 de conformation ⁴C₁
et de 3,6 anhydro-galactose de conformation ¹C₄ lié en 1 et 4.
1 sulfate pour deux motifs sucro.

CARRAGHÉNANE GÉLIFIANT

Le lota carraghénane est formé par un enchainement de
β - D- galactoses, 4-sulfate llé en 1 et 3 de conformation ⁴C₁
et de 3,6 anhydro-galactose de conformation ¹C₄ llé en 1 et 4.
2 sulfates pour deux motifs sucre.

CARRAGHÉNANE ÉPAISSISSANT

Le Lambda carraghénane est formé par un enchaînement de
β - D- galactoses, 2-sulfate lié en 1 et 3 de conformation ⁴C₁
et d'un α - D- galaclose, 2,6 disulfate de conformation ⁴C₁
llé en 1 et 4.
3 sulfates pour deux motlfs sucre.

BOTANICAL SOURCE

Commercial production of carrageenan has evolved in France from the “lichen” collected along the French coastal areas.

The “lichen”, a blend of Chondrus crispus and Gigartina stellata is still harvested along the shores of Normandy and Brittany. Collection is done by hand gathering, at ebb tide, between spring and autumntides.

The “lichen” remains the major source of carrageenan production. Other seaweed sources, however, can be used to obtain products of desired property or combination of properties sulted to the customers' applications.

Répartition géographique des différentes algues rouge

Geographical distribution of various red seaweeds

FRACTIONS OF SOME RED SEAWEEDS SPECIES

GEOGRAPHICAL REPARTITION OF VARIOUS RED SEAWEEDS

EXTRACTION PROCEDURE

Extraction process for industrial production of carrageenan is based on its two main properties. Carrageenan is :
soluble in hot water.
insoluble in polar organic solvents.

EXTRACTION

After washing, seaweeds are extracted with hot water. Crushing of the seaweeds under alkaline conditions is carried out to promote a more total extraction of the polysaccharide.

PURIFICATION

The hot aqueous extract filtered in the presence of a filter aid (diatomaceous earth) passes through a sieve under pressure. A transparent syrup containing carrageenan in solution is thus obtained.

CARRAGEENAN RECOVERY

Carrageenan is recovered from this syrup by alcohol precipitation. As carrageenan coagulates, it forms fibers and impurities remain in solution.

The coagulum is pressed, washed in a high-titrated alcohol to complete its dehydration, dried by evaporation under vacuum, then milled to a desired particle size.

This process allows the product to be of high purity. The white to white-beige powder obtained is tasteless and odorless.

Uses of Carrageenan

Kappa: Gelling Agent (Hot water, milk)

• dairy desserts (milk-gels, flans, custards)
• chocolate milks
• ices, ice creams and related products
• meat preserves
• petfoods
• air-fresheners
• enzyme
• in vitro meristem culture

Iota: Gelling Agent (Hot water, milk)

• dairy desserts
• sauces and salad dressings
• ices, ice creams and related products
• cosmetics

Lambda: Thickener

• dairy desserts
• salad dressings and sauces
• toothpastes
• cosmetics

PRODUCTION,
PROPERTIES
AND
USES
OF
AGAR

STRUCTURE

BOTANICAL SOURCE

Gelidium sesquipedale.	Gelidium latifolium.
(Source: Les algues des côtes françaises, P.GAYRAL, Ed. DOIN, 1966)

Pterocladia capillacea.
(Source: Les algues des côtes françaises, P.GAYRAL, Ed. DOIN, 1966)

EXTRACTION PROCEDURE

AGAR FABRICATION DIAGRAM

NEW EXTRACTION PROCESS FOR BACTERIOLOGICAL QUALITY AGAR-AGAR FROM SESQUIPEDALE GELIDIUM RED ALGA
I - DISCOLOURATION OF EXTRACTION JUICES

Eliminating chromophores from sesquipedale geledium red alga of native β-carotene or degradated phycobiliary group, was carried out in the presence of chloride macroporous anionic resins, most efficient system requires a continuous system involving a compact resin bed under ascending current. Resins are regenerated by a sodium chloride solution and are not affected by successive cycles.^1,2

NEW EXTRACTION PROCESS FOR
THE BACTERIOLOGICAL QUALITY AGAR-AGAR
II - ELIMINATION OF THE MINERAL CHARGE

The endogenous mineral charge from sesquipedale Gelidium alga is studied. This charge released in the agar-agar extraction juice, accounts for the high mineral content in agar-agar extraction juices. Demineralisation is carried out by ion-exchange resins. Sodium gel resins prove to be the most efficient. A sodium/heavy cation exchange eliminates major part of heavy cations. Gelling the agar-agar solution permits its separation by mechanical pressing-out or freezing-defrosting. The caking or agar-agar micells recovered are almost rid of all sodium chloride released in water, whilst conforming to bacteriological agar-agar quality in the residual mineral composition. Resins are regenerated by simple sodium chloride solution without being affected by successive cycles.^1,2

R. LEBBAR, A. ZIOUANI, M. DELMAS* and A. GASET

Laboratoire de Chimie des Agroressources
Ecole Nationale Supérieure de Chimie de Toulouse
Institut National Polytechnique de Toulouse
118 route de Narbonne, 31077 Toulouse Cedex, France

* To whom correspondence should be sent

APPLICATIONS

The major role of hydrocolloids in food preparations is based on water-binding capacity and their ability to modify the rheological behaviors in order to obtain a desired functionality suited to the application.

The selection factors will be interdependent with the conditions of use:

• pH-value of the system,
• Presence of electrolytes,
• Heat-treatments,
• Stability to storage.

All colloids do not perform in the same manner to these different parameters.

HEAT TREATMENTS

Apart from pectins; which are partially depolymerized, most hydrocolloids withstand heat treatments of pasteurization and sterilization when used in system at pH-values near neutrality.

STABILITY TO STORAGE

It depends on the modification liable to occur in the macromolecule associations. Too great junction zones will lead to syneresis. The latter can be avoided by the addition of macromolecules which induce perturbations in these multiple associations.

IN ACID SYSTEM

In an acid system hydrocolloids, apart from pectins and xanthan gum display a propensity for hydrolysing as a result of the combination temperature/duration. In such a process acid should be added finally which reduce depolymerization.

ELECTROLYTES INTERACTIONS

These interactions have been described with regard to gelation and particularly to the gelation of alginates and pectins. When they are used in presence of calcium, these electrolytes assist in creating junction zones required for gelation but sometimes they should be sequestrated to allow the colloid to be hydrated.

Hydrocolloids are used in foods essentially as:

Thickening     Gelling

Very soluble hydrocolloids which show no capacity to create junction zones:

Galactomannans,
Lambda Carrageenan.
Alkaline Alginate.
Nanthan gum.

Some typical uses in foods:

• Sauces, salad dressings and related products,
• Soups and thick soups,
• Custards type “dessert-creams”,
• Binding agents for meat products.
• Instant products,

The major properties of this type of hydrocolloids are as follow:

hot water soluble. Form gels when cooled to room temperature (thermally reversible gels).

cold water soluble. Form gels in presence of reactive salts.

hot water soluble. Form gels in presence of acid (non-thermoreversible gels). Because of the wide range of possible variations exhibited by the intramolecular associations, textures can be modulated at will to obtain the desired functionality. For this purpose. combinations of colloids are often selected.

Thermally reversibles gels

Low-methovy pectins.
κ-carrageenan with gels rigid in texture.
ι-carrageenan with resilient and thirotropic gels.
κ-carrageenan and locust bean gum with a cohesive and resilient texture.
Gelatin

Some typical uses in foods:

• Milk-gels type flans.
• Flavored milk-gels type gellified milks.
• Water-gels, low-sugar jams and coverings.
• Meat preserves (canned meat), pet-foods, aspics.
• Confectionery.

Gelling     Stabilizing

Light or non-thermoreversible gels

• Alkaline alginate in presence of a low-reactive acid or in presence of a calcium salt. According to the rate of use of Ca^--, the gel may be slightly thermoreversible or on the contrary completely irreversible.
• High methoxy pectins (HM pectins) in presence of acid and sugar.
• Low-methoxy pectins (LM pectins) in presence of Ca^-- (saturation of the pectic gel).

Some typical uses in foods:

• Jams and Jellies,
• Jellified confectionery: fruit jellies,
• Meat-preserves (canned meats), pet-food.
• Restructured foods (reformed fruits, various food analogs).

The separations between the various phases of a mix can be avoided by:

• a thickener which will act by an increase in viscosity,
• a gelling agent at low usage level apt to create a three-dimensional network.
• or a combination of thickeners and gelling agents.

Some typical uses in foods:

• Emulsified sauces, salad dressings,
• Ice-creams and related products,
• Chocolate milks,
• Fruit beverages.

Principales applications des colloïdes algaux.
(Source: BIOFUTUR, Mars 1990)

Uses of Agar

Food Industry (58%)

Strong gelling agent, thickener, stabilizing agent

• jellies and candies
• marmalade
• mitsumame production
• bakery</li>
• fruit jelly preparations
• yoghurt
• soft boiled sausages in meat industry
• canned products
• chicken, tongue, fish in gelatin</li>

Pharmacy

• gel forming agent, excipient
• smooth laxative
• stabilizer, dispersive

Biotechnology

Bacteriological Agar (28%)

• Deionized agar
• Culture Media
• Bacteriology, Mycology
• Insects Media
• In vitro culture vegetables, flowers, trees
• Agarose
• Biochemistry
• Immunology
• Genetic engineering industry
• Beads