Relation between structure and rheological/thermal properties of agar. A mini-review on the effect of alkali treatment and the role of agaropectin

Since agar has been used for various applications such as gelling agents in food industry, culture medium in microbiology, gel elecrophoresis in biotechnology, and in pharmacy by virtue of its potential bioactivity, the relation between the structure and physico-chemical/physiological properties has been studied extensively. To develop further utilisation, the relation between the structure and properties for agar materials from seaweeds not from chemical reagents sold by chemical industrial companies is discussed in the present paper. Reducing sulphate content and increasing 3,6-anhydro-l-galactose by alkali treatment led to the increase in gelling ability, however the optimum condition of alkali treatment (alkali concentration, temperature, time) was shown to depend on the species, the production place, and harvesting season of seaweeds. As the detailed study of agaropectin which does not form a gel by itself has not been done so much because of its complexity of the structure, its role in the gelation of agar is discussed. It was shown that agaropectin did not inhibit the gelation of agar but rather enhances the gelation.