Agar is hydroclloid composed by polysaccharides extracted from red seaweeds of the Rhodophyceae class. Its structure is mainly composed by repeated and alternated units of Dgalactose and L-3,6 anhydrogalactose, which joinly form Agarobiose disaccharide, presenting some substitutions or modifications on the molecular chain, like:

>> Methoxylation (-O-CH3), occurs mainly on C-6 of the D-galactors. Substitution by methy groups is positively correlated to gelling temperature.

>> Sulphation (-O-SO3), probably occurs mainly on C-2 of the L-galactose. Agar may contain up to 5-6 % SO4. Substitution by sulphate esters is negatively correlated to gel strength.

>>Pyruvation (-O-C(CH3)(COOH)-3, as a ketal coupled onto C-4 and C-6 of the D-galactose. Agar may contain up to 30% pyruvate and it is not believed to affect gelling properties.

Whereas methoxylation seems to occur reqularly on the molecutar chain, sulphation and pyruvation are rather irreqular

As a simple definition for Agar, we would say that it is composed by two groups of polysaccharides ( see Fig. 1):

>> Agarose, which corresponds to the neutral and lineal part of the molecule, which is able to form a stroung gel. It is believed that the absence of charged groups, as sulphates, enable it to form gel, as well as the molecule neutrality.

>> Agaropectin, is the charged part of the molecule. The presence of sulphated groups would help to form a more colloidal structure, which would not gellify as strong as a linal molecule. Since the molecule is negatively charged, there is a repulsion between them, which would contribute to form a soft gel.

Nevertheless, Agar is now considered to a complex mix of polysaccharides, all on a same structural basis, but with different grade of charged groups substitution.

Considering the almost infinite number of possible combinations between sulphate esters, methyl groups and pyruvic acid among others, three fraction are suggested:

1. Neutral Agarose

2. Pyruvatd agarose with little sulphate

3. A sulphated galactose

Agar structure is not yet known in full details, so the probably new studies will be presented in the future.

Agar is the main polysaccharide that forms part of the matrix of the cellular wall of agarophyte seaweed from the Rhodophyceaae class. I

It is considered a great source of dietary fiber, about 65 to 80 grams of the dry weight of 100 grams of agar consist of dietary fiber. This type of dietary fiber is not easily digested by the human body, and thus forms a key ingredient in mild laxatives. When consumed in moderates amounts, dietary fiber also prevents cholesterol from being absorbed in the intestine. It is for this reason that dietary fiber form part of many low calories dietary supplements

* For quite some time, Biomedical group of Takara Shuzo Co., Ltda. has been conducting research in agar, demonstrating the agar oligosaccharide (derrived from the polysaccharide agarose) can cause human cancer cells to undergo apoptosis ( self destruction ).

* Futher research conducted by Biomedical Group has revealed that agar oligosaccharide demonstrated cancer curing properties, as well as the preventive effect against cancers. Agar oligosaccharide has also been found to prevent and cure arthritis, as well as other inflammatory diseases of the joints