Chemical Properties
moisture <12%, gel strength 1,000 g/cm2, pH 7-9
Chemical Properties
Carrageenan, when extracted from the appropriate seaweed source,
is a yellow-brown to white colored, coarse to fine powder that is
odorless and tasteless.
Chemical Properties
Carrageenan is a generic term used for chemically similar hydrocolloids obtained by aqueous extraction from certain
members of the class Rhodophyceae. Carrageenan is a strongly charged anionic polyelectrolyte of large size. It is generally regarded
as containing two major fractions, which may be separated from dilute aqueous solution by the precipitation of one fraction by the
addition of potassium ions. The precipitated fraction, or gelling fraction, is designated k-carragenan, and is composed of residues
of D-galactose and 3,6-anhydro-D-galactose in a molar ratio of 1.1 to 1.5:1 and contains one sulfate half-ester group for every 2 to
2.5 monosaccharide units, depending on the source. l-Carrageenan, the nongelling fraction, is composed primarily of 1,3-linked
D-galactose-2-sulfate and 1,4-linked D-galactose-2,6-disulfate. The sulfate content of the two fractions differs substantially, with
values of approximately 24 and 33% having been given for the k and l fractions, respectively. Carrageenan is readily soluble in water,
but it has few other solvents. In the presence of specific metallic cations, such as potassium, calcium, ammonium and others, carrageenan solutions form short, inelastic, thermally reversible gels on heating and cooling. The most unique property of carrageenan
as a hydrocolloid is its high degree of reactivity with certain proteins; its reactivity with milk protein, in particular, is the basis for a
number of applications of carrageenan in foods. Carrageenan is practically odorless and has a mucilaginous taste.
Occurrence
Irish moss is a seaweed found in Europe and on the coasts of Canada.
Uses
Pharmaceutic aid (suspending
agent); pharmaceutic aid (viscosity-increasing agent).
Uses
Carrageenan is a gum that is a seaweed extract obtained from red
seaweed chondrus crispus (also known as irish moss), gigartina, and
eucheuma species. chondrus crispus yields kappa and lambda carra-
geenans. gigartina yields kappa and lambda carrageenans. eucheuma
yields kappa and iota carrageenans. it exists as various salts or mixed
salts of a sulfate ester. it is classified mainly as kappa, iota, and
lambda types which differ in solubility and gelling properties. the
kappa and iota types require hot water (above 71°c) for complete
solubility and can form thermally reversible gels in the presence of
potassium and calcium cations, respectively. the kappa gels are brit-
tle with syneresis while the iota gels are more elastic without synere-
sis. the lambda type is cold-water soluble and does not form gels.
kappa and iota carrageenan are very reactive with milk protein
products. carrageenan is used to stabilize milk protein at 0.01–0.05%
and to form water gels at 0.5–1.0%. its uses include dairy products,
water gel desserts, and low-calorie jellies. a typical use level in water
systems is 0.2–1.0% and milk systems is 0.01–0.25%. also termed
chondrus extract.
Uses
Carrageenan is a species of red seaweed known as chondrus crispus, from which kappa and lambda carrageenans are obtained.
Definition
A sulfur phycocolloid: the aqueous, usually gel-
forming, cell-wall polysaccharide mucilage found
in red algae (Chondrus crispus and several other
species). It is water-extracted from a seaweed called
carrageen or Irish moss (east coast of southern
Canada, New England, and south to New Jersey). It
is a mixture of polysaccharide fractions: (1) The λ
fraction is cold-water soluble, contains d-galactose
and 35% esterified sulfate, and does not gel. (2) The
κ fraction contains d-galactose and 3,6-anhydro-d-
galactose (1.4:1 ratio) and 25% esterified sulfate.
The κ form does not gel without addition of a solute;
the properties of the gel depend on the amount and
nature of the added solute. Another species of sea-
weed produces 100% κ from North Carolina to the
tropics. Carrageenan is a hydrophilic colloid that
absorbs water readily and complexes with milk pro-
teins.
Production Methods
The main species of seaweed from which carrageenan is manufactured
are Eucheuma, Chondrus, and Gigartina. The weed is
dried quickly to prevent degradation, and is then baled for shipment
to processing facilities. The seaweed is repeatedly washed to remove
gross impurities such as sand, salt, and marine life, and then
undergoes a hot alkali extraction process, releasing the carrageenan
from the cell. Once it is in a hot solution, carrageenan undergoes
clarification and concentration in solution and is converted to
powder.
Three processes can be used to remove the carrageenan from
solution. The first is a ‘freeze–thaw’ technique. The solution is gelled
with various salts, then the gels are frozen. Upon thawing, the water
is removed and the resultant mass, primarily carrageenan and salt,
is ground to the desired particle size.
The second method, referred to as the ‘alcohol precipitation
method’ takes the concentrated solution of carrageenan and places
it in alcohol. This causes the carrageenan to precipitate out of
solution. The cosolvents are evaporated and the precipitated
carrageenan is dried and ground to the desired particle size.
The third method is the ‘KCl precipitation’ process, where after
hot extraction, the filtrate is evaporated to reduce the filtrate
volume. The filtrate is then extruded through spinnerets into a cold
1.0–1.5% solution of potassium chloride. The resulting gel threads
are washed with KCl solution and are pressed, dried and milled to
carrageenan powder. Commercial carrageenan is usually standardized
by blending different batches of carrageenan and adding
sugar or salt to obtain the desired gelling or thickening properties.
brand name
Marine Colloids (FMC).
General Description
Carrageenans are mucopolysaccharides from the cell walls of the red algae. They are anionic linear polymers composed of 1,3α-1,4β-galactans having one (κ-), two (ι-) or three (λ-) sulfates per disaccharide unit. In ionic solutions, κ- and ι-carrageenans self-associate into helical structures that form rigid or flexible gels, respectively. λ-carrageenans do not form helices and are non-gelling. Carrageenans are used commercially as thickeners and stabilizing agents.
Hazard
Questionable carcinogen.
Pharmaceutical Applications
Carrageenan is used in a variety of nonparenteral dosage forms,
including suspensions (wet and reconstitutable), emulsions, gels,
creams, lotions, eye drops, suppositories, tablets, and capsules. In
suspension formulations, usually only the ι-carrageenen and γ-carrageenan
fractions are used. γ-Carrageenan is generally used at
levels of 0.7% w/v or less, and provides viscosity to the liquid.
Carrageenan has been shown to mask the chalkiness of antacid
suspensions when used as a suspending agent in these preparations. When used in concentrations of 0.1–0.5%, carrageenan
gives stable emulsions. Carrageenan is used in hand lotions and
creams to provide slip and improved ‘rub out’.
ι-Carrageenan develops a shear-thinning thixotropic gel, which
can be easily poured after shaking. When ι-carrageenan is used, the
presence of calcium ions is required for the gel network to become
established. With pure ι-carrageenan, about 0.4% w/v is required
for most suspensions plus the addition of calcium. However, if
SeaSpen PF is used, it must be at about 0.75% w/v level, although
no additional calcium is required as this is already present in the
product to control the rate of gelation.
Studies on the effect of carrageenan and other colloids on mucoadhesion
of drugs to the oropharyngeal areas have shown that
carrageenan had the greatest propensity for adhesion and can be
used in formulations for oral and buccal drug delivery.
The application of carrageenan in topical gel bases has been
examined, and the findings indicate that the use of carrageenan
in these dosage forms is most likely to be dependent on the active
drug, owing to the potential for ionic interactions.
In the case of topical gels, a combination of ι, κ-, and γ-carrageenans
produces a spreadable gel with acceptable tactile
sensation, resulting in drug release that is more likely to follow
diffusion kinetics.
Incorporation of carrageenan into tablet matrices with various
drugs and other excipients to alter release profiles has been studied,
illustrating that the carrageenans have good tablet-binding properties. Furthermore, the inclusion of calcium or potassium salts
into the tablet creates a microenvironment for gelation to occur,
which further controls drug release.
There have also been several references to the use of carrageenan
in chewable tablets having a confectionary texture. This
approach to creating a novel dosage form requires the use of both icarrageenan
and κ-carrageenan, to prevent moisture loss and
texture changes that occur over time.
Carrageenan has been used for the microencapsulation of
proteins and probiotic bacteria. Hydrogels have also been
prepared by crosslinking with gelatin and k-carrageenan for oral
delivery of probiotic bacteria. It has also been used as beads in
the preparation of controlled release systems. Hydrogel beads
based on κ-carrageenan and sodium alginate/chitosan are being
used as new carriers for drug loading and controlled delivery
systems. κ-Carrageenan is known as a novel pelletization aid
in the manufacture of pellets by extrusion/spheronization and has
the best pelletization behavior. γ-Carrageenan is also able to
nanoencapsulate drug molecules spontaneously, hence controling
drug release. The presence of carrageenan induces the formation
of smaller particles compared to those formed in the absence of
polymer, and their average size depends on the nature and
concentration of the polysaccharide used.
Studies have shown that carrageenan compounds block infections
by the herpes simplex virus; human cytomegalovirus;
human papilloma virus; Sindbis virus; vesicular stomatitis virus;
and HIV. A combined κ- and γ-carrageenan formulation is
currently being investigated as the active ingredient in a topical
microbicide used to prevent the sexual transmission of HIV. In
combination with chitosan, agar and polyvinyl pyrrolidone,
carrageenan forms a water-insoluble complex which is able to
absorb large amounts of body fluids, and is used as an effective
wound dressing. Carrageenan is used in the preparation of
hard and soft capsule shells. It is also used in toothpastes and
cosmetic preparations such as conditioners and shampoos.
Agricultural Uses
Carrageenans are naturally occurring hydrophilic
colloids found in various species of red seaweeds.
They perform a role similar to cellulose in terrestrial
plants.
Carrageenans are a highly sulphated galactan. Due
to this they are a strongly anionic polymer which makes
them useful commercially. They are commercially
extracted for their use as water soluble gums.
Carrageenans may be compared with furcellaran
extracted from agars (furcellarans have a smaller
proportion of half-ester sulphate). Agars, in contrast, are
commonly considered non-ionic
Safety Profile
Poison by intravenous
route. Questionable carcinogen with
experimental neoplastigenic and tumorigenic
data. When heated to decomposition it
emits acrid smoke and fumes.
Safety
Carrageenan is widely used in numerous food applications and is
increasingly being used in pharmaceutical formulations. Carrageenan
is generally regarded as a relatively nontoxic and nonirritating
material when used in nonparenteral pharmaceutical formulations.
However, carrageenan is known to induce inflammatory
responses in laboratory animals, and for this reason it is frequently
used in experiments for the investigation of anti-inflammatory
drugs. Animal studies suggest that degraded carrageenan
(which is not approved for use in food products) may be associated
with cancer in the intestinal tract, although comparable evidence
does not exist in humans.
The WHO has set an acceptable daily intake of carrageenan of
‘not specified’ as the total daily intake was not considered to
represent a hazard to health. In the UK, the Food Advisory
Committee has recommended that carrageenan should not be used
as an additive for infant formulas.
LD
50 (rat, oral): >5 g/kg
LD
50 (rabbit, skin): >2 g/kg/4 h
LC
50 (rat, inhalation): >0.93 mg/L
storage
Carrageenan is a stable, though hygroscopic, polysaccharide and
should be stored in a cool, dry place.
Carrageenan in solution has maximum stability at pH 9 and
should not be heat processed at pH values below 3.5. Acid and
oxidizing agents may hydrolyze carrageenan in solution leading to
loss of physical properties through cleavage of glycosidic bonds.
Acid hydrolysis depends on pH, temperature and time. The acid
hydrolysis takes place only when the carrageenan is dissolved, and
the hydrolysis is accelerated as the processing temperature and/or
the processing time is increased. However, when the carrageenan is
in its gelled state the acid hydrolysis no longer takes place.
Purification Methods
This D-galactose-anhydro-D or Lgalactoside polysaccharide is precipitated from 4g of Carrageenan in 600mL of water containing 12g of KOAc by addition of EtOH. Collect the fraction that precipitates between 30 and 45% (v/v) of EtOH and dry them in vacuo. [Pal & Schubert J Am Chem Soc 84 4384 1962.]
Incompatibilities
Carrageenan can react with cationic materials. If complexation of
cationic materials, with associated modification of the active
compound’s solubility, is undesirable, the use of carrageenan is
not recommended.
Carrageenan may interact with other charged macromolecules,
e.g. proteins, to give various effects such as viscosity increase, gel
formation, stabilization or precipitation.
Regulatory Status
GRAS listed. Accepted as a food additive in Europe. Included in the
FDA Inactive Ingredients Database (dental; oral capsules, granules,
powders and syrups; topical; transdermal preparations; and
controlled-release film preparations). Included in the Canadian
List of Acceptable Non-medicinal Ingredients. Included in nonparenteral
medicines (oral granules, capsules (shells), and orodispersible
tablets) licensed in the UK.
