Читать книгу Polysaccharides - Группа авторов - Страница 117

The last decade has been remarkable for agar. A number of researches were made to obtain agar of greater gel strength and of lower dissolving power at higher temperature (mainly above boiling temperature of water i.e. 100 °C). Commonly, 20 min time is sufficient to completely dissolve agar in water, while maintaining the gel strength. Strength of commercially produced agar gel is mainly depends upon its repeating units of agarose in relation to their agaropectin contents. Agarose content in agar also determines its solubility in different solvents. It has been observed that agarose with molecular of 240 kD or higher, takes more time than the agaroses with lower molecular weight. Nonetheless agarose with even higher molecular weight require extra pressure and higher temperature around 121 °C or higher. A faster solution for this is xerogels. Xerogels are most hydrophilic structures and obtained by milling the dehydrated gel with synergies. This results in a fine grounded powder that bloats a lot due to more contact with the warm water and larger number of agarobiose molecules.

When agar is dissolved in water, its viscosity is decreased and which helps agar in dissolving nicely into water. It should be taken into account, when adequate amount of calcium ions are present between various agaropectins and helps them building structure of higher molecular weight, it helps in reducing the viscosity of agar in water. These ionic bonds have tendency to distort the molecular weight statistical measurements of agar. These ionic bonds emerge only when calcium or any other alkali metals are there in the agar. Agar solutions can be prepared faster with addition of influencing substances before extraction and drying of agar. However, agar prepared using these determining substances may cause problem when a batch experiment of agar will be needed.