BY- PALASH D
In addition to edible and other direct uses,
marine algae provide a rich and diverse source
of raw material for the manufacture of seaweed
gums, a group of natural compounds
characterized by their thickening and gelling
properties. Such compounds find wide
application in the food, pharmaceutical and
Agar is polysaccharides derived from algae. They are
hydrocolloid sources, with many applications in the food,
pharmaceutical, cosmetic, biotechnology industries as gelling
agents, thickeners or stabilizing and emulsifying agents. Agar
constitute two well defined families of polysaccharide,
derived from different genera in Rhodophyta, collectively
known as agarophytes .
The basic structure of agar is a regularly alternating
sequence of 3-1-galactose and 4-linked 3,6-anhydro-L-
The steps required to obtain agar from seaweed are -
1. Cleaning of seaweed
2. Chemical pre-treatment
3. Extraction of seaweed
4. Filtration and gelation of extract
5. Bleaching and dewatering of gel
Agar is insoluble in cold water and the seaweed
may safely be washed with water to remove
impurities, such as salt, as well as to assist in the
separation of foreign matter, such as other
CLEANING OF SEAWEED
Alkali pre-treatment has been found to be the most
useful for a product of higher gel strength being
The purpose of alkali treatment is that increased gel
strength results from production of 3, 6-
anhydrogalactose units induced by alkaline hydrolysis of
galactose-6-sulphate groups within the agar molecule
also to soften the weed and prepare it for extraction.
Agar is extracted from seaweed using hot water. Although
adjustment of the pH is sometimes beneficial, and the use of
certain additives, such as phosphates, is claimed to improve
yields or colour.
The seaweed is usually added to boiling water in the extraction
vessel, which is heated either by live steam introduced through
pipes at the bottom of the vessel.
After addition of the seaweed, boiling is continued for between 1
and half to 3 hours.
Samples of extract and weed at intervals and tests them with
fingers; good gel formation and the right ‘feel’ when the weed is
pressed between the fingers indicate that extraction is complete.
FILTRATION AND GELATION OF THE
On completion of the extraction, the hot aqueous extract is
allowed to drain through a metal screen at the bottom of the
holding vessel. The screen retains the bulk of the seaweed
residue and allows the liquid extraction to pass through several
layers of filter cloth. These remove finer, particulate matter.
the long established method of freezing and thawing the gel is universally used. The
freeze-thaw cycle is critical not only to the successful dewatering of the gel but to the
attainment of a good quality product as well, the cold thaw water, in which the agar is
insoluble, removing low molecular weight polysaccharides, salts and pigments.
Within a few hours of forming a gel (no more than 24 hours, otherwise the gel
deteriorates) the trays of agar are placed in a freezer, where they are stored for periods
of at least 20—24 hours (and sometimes as long as 72 hours) at temperatures ranging
from — 10 to — 20°C. The process of freezing should be slow rather than rapid so that a
uniformly frozen gel matrix is obtained. To help achieve this, the agar gel is ‘combed’ with
a metal ‘comb’ before placing it in the freezer; this also makes the subsequent washing
and drying more efficient and gives the finished product its characteristic mat-like
After removing the trays from the freezer, the agar is allowed to thaw, then washed with
and bleached, usually by immersing in tank containing hypochlorite solution. Treatment is
generally not more than 10— 15 minutes. The agar is washed again several times,
before finally being laid put on mesh screens to dry in the sun.
BLEACHING AND DEWATERING OF THE
APPLICATION IN FOOD
INDUSTRYGelagar is a complete range of tailored food grade agar agar powders
especially developed to be used in all different confectionery, jam and
Different Gelagar types have been developed for the following
applications : fruit jellies , Jams ,soft candies , gelatines . bakery
fillings ,ice creams , puddings and marshmallows
DENTALDentagars are technical agar powders to be used in
dental impression applications.
Dentagars are offered with different gel strengths and
APPLICATION IN PHARMA
Pharmaceutical Agar is used in the pharmaceutical
industry for many applications such as suspending
agent for Barium Sulphate Radiology, intestine
regulation, surgical lubricants and in preparations of
emulsions, suspensions, capsules, etc.
APPLICATION IN LABS
Bactagars are very pure bacteriological grade agar powders
extracted only from very selected seaweed Gelidium.
Bactagar system is the perfect media for bacteria growth and
can be used in all bacteriological applications.
Bactagars are offered with low, medium and high gel
Unbleachagar system offers very special unbleached
agar powders for health food applications extracted from
very selected seaweeds Gelidium and Gracilaria of
Unbleachagar offers agar agar powders having different
properties but the common characteristic is the
extremely low content of chlorophorm and chlorine.
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