Departement Ressources Vivantes
Laboratoire d'Algologie Applique
Nantes cedex 01, France
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.
|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
|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.
|homogeneous blocks of mannuronic acid residues||M.M.M.M|
|homogeneous blocks of guluronic residues||G.G.G.G|
|alternating blocks of these two acid residues||M.G.M.G|
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:
|Stipes of Laminaria hyperborea||0.6|
These seaweeds display large variations in mannuronic/guluronic proportions.
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.
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.
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.
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:
The final product is then dried, milled and sieved to the desired particle size.
Production of sodium alginate
|INSOLUBLE CALCIUM AND MAGNESIUM SALTS OF ALGINIC ACID IN SEAWEED|
|↓Na2CO3 (alkaline extraction)|
|SOLUBLE SODIUM ALGINATE PLUS INSOLUBLE SEAWEED RESIDUE|
|SODIUM ALGINATE SOLUTION|
|INSOLUBLE CALCIUM ALGINATE||↓|
|INSOLUBLE ALGINIC ACID||INSOLUBLE ALGINIC ACID|
|Na2CO3 or NaOH↓||↓Na2CO3 or NaOH|
|SODIUM ALGINATE||SODIUM ALGINATE|
|CALCIUM ALGINATE PROCESS||ALGINIC ACID PROCESS|
Uses of Alginate
In the presence of calcium and acid
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.
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 following fractions have been mainly determined:|
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.
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.
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.
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.
|G. skottsbergii||Argentina - Chile|
|G. chamissoi||Peru - Chile|
|C. crispus||France - North Atlantic|
|E. cottonii||The Philippines|
|H. muciformis||Brazil - Senegal|
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.
|Fractions of some|
RED SEAWEEDS species
|Ggartina stellata||κ + ι + λ|
Répartition géographique des différentes algues rouge
Geographical distribution of various red seaweeds
FRACTIONS OF SOME RED SEAWEEDS SPECIES
GEOGRAPHICAL REPARTITION OF VARIOUS RED SEAWEEDS
|G. skottebergii||→||Argentina - Chlle|
|G. chamissoi||→||Péru - Chlle|
|C. crispus||→||France - North Atlantic|
|E. cottonii||→||The Phillppines - Indonesia|
|H. muciformis||→||Brazil - Senegal|
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.
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.
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 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)
Iota: Gelling Agent (Hot water, milk)
|Gelidium sesquipedale.||Gelidium latifolium.|
|(Source: Les algues des côtes françaises, P.GAYRAL, Ed. DOIN, 1966)|
(Source: Les algues des côtes françaises, P.GAYRAL, Ed. DOIN, 1966)
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
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:
All colloids do not perform in the same manner to these different parameters.
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.
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:
Very soluble hydrocolloids which show no capacity to create junction zones:
Some typical uses in foods:
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
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.
Some typical uses in foods:
Light or non-thermoreversible gels
Some typical uses in foods:
The separations between the various phases of a mix can be avoided by:
Some typical uses in foods:
|Pastagar A — Pastagar B|
Powdered bacteriological agars
|Pastagars A and B are specially purified for the preparation of bacteriological|
They conform to the standards of the American Pharmacopoeia,
|Pastagar A is an american type agar with weak gelling ability. Used at concentrations of 1.5 to 1.7 % the agar is firm and clear. It can also be used at lower concentrations (0.1 to 0.6 %) for the detection of motility and for growing anaerobic and micro-aerophilic organisms.|
|Pastagar B is a european type agar with strong gelling ability. Used at concentrations of 1.2 to 1.4 %, the agar is firm and clear. It can also be used at lower concentrations (0.05 to 0.5 %) to study motility and to grow anaerobic and micro-aerophilic organisms. The pH of a 1.5 % solution in distilled water is 7.2 ± 0.3; those media prepared with one of the two Pastagars (A or B) are therefore near neutrality.|
|Quality control||Quality control ensures that all batches of Pastagars A and B conform to a predetermined standard. This is a continuous process, testing the purity of the raw materials, surveying the manufacturing procedures, and carrying out physical, chemical, bacteriological and performance tests.|
|Average characteristics||Pastagar A||Pastagar B|
|Appearance||Cream-white powder||Cream-white powder|
|Density||0.6 to 0.7||0.6 to 0.7|
|Odour||Slight, non-putrid||Slight, non-putrid|
|Gel strength before and after autoclaving Transparency(Nephelos Coleman) before and after autoclaving||500 to 700 g/cm||Greater than 700 g/cm|
|Less than 50 NC||Less than 50 NC|
|655 nm filter||0.010 to 0.020||0.010 to 0.020|
|525 nm filter||0.020 to 0.050||0.020 to 0.050|
|430 nm filter||0.050 to 0.150||0.050 to 0.150|
|Befor autoclaving||7.2 = 0.3||7.2 = 0.3|
|After autoclaving||7 = 0.6||7 = 0.6|
|Hydration||Less than 12 %||Less than 12 %|
|Ash||Less than 7 %||Less than 3 %|
|Sieve no 18||0||0|
|Sieve no 35||Less than 5 %||Less than 5 %|
|Sieve no 60||Less than 25 %||Less than 25 %|
|Sieve no 150||Less than 50 %||Less than 50 %|
|Sieve no 350||Less than 25 %||Less than 25 %|
|Sieve no > 350||Less than 5 %||Less than 5 %|
|Precipitation after autoclaving||None||None|
|Melting temperature||89 = 4 °C||89 = 4 °C|
|Gelling temperature||35 = 5 °C||35 = 5 °C|
|Contamination with thermophilic spores||None||None|
Principales applications des colloïdes algaux.
(Source: BIOFUTUR, Mars 1990)
|Domaine d'application||Fonction||Pourcentage de la demande|
|ALGINATES||TEXTILE||épaississant pour la páte contenant le colorant||50%|
|AGRO-ALIMENTAIRE||épaississant, gélifiant, émulsifiant, stabilisant, rétenteur d'eau||30%|
|PAPIER||film protecteur lors de la fabrication et de l'encrage||6%|
|BAGUETTES DE SOUDURE||enrobage (contróle des conditions thermiques et gazeuses au contact la soudure)||5%|
|PRODUITS PHARMACEUTIQUES||agent dispersant pour compnmés, épaissant, gélifiant||5%|
|CARRAGHENANES||PRODUITS LAITIERS||gélifiant, epaissant, stabilisant (interactions avec les protéines)||52%|
(dentifnces, ciffuseurs, cosmetiques)
|gélifiant, viscosifiant en particulier en association avec ces polyols||22%|
|AGARS||AGRO-ALIMENTAIRE||puissant gélifiant, epaississant||58%|
|PHARMACIE & TECHNIQUES BIOCHIMIQUES||excipient, axatif, agent dispersant, agent ce separation (agarose)||14%|
|BACTERIOLOGIE||support de culture||28%|
(CULTURE IN VITRO)
|support de culture||non estime|
Uses of Agar
Food Industry (58%)
Strong gelling agent, thickener, stabilizing agent
Bacteriological Agar (28%)