Life Sciences

Agar is a natural polysaccharide extracted from red algae, primarily species of the genera Gelidium and Gracilaria. Agar is composed of two primary components: agarose and agaropectin. It is widely used in the food industry, pharmaceutical industry, bioengineering and other fields. It has coagulation and stability and is often used as a thickener, coagulant, suspending agent, emulsifier, stabilizer and preservative.

Solubility
At room temperature, agar is neither soluble in water nor in inorganic and organic solvents. It is only slightly soluble in ethanolamine and formamide, but it can be dissolved in water and some solvents under heating conditions.

Dried agar can absorb water and swell at room temperature, and the water absorption rate can reach 20 times. It can be dissolved in water to form a solution when heated to 95℃. Agar solution can form gel at room temperature. Compared with other substances that can form gel, it has the strongest gel ability at the same concentration. Even a 0.1% agar solution can solidify at around 30℃.

Agar can also be dissolved in boiling low-concentration ethanol (30% - 50%) solutions. In some high-concentration electrolyte solutions, such as sodium sulfate, magnesium sulfate or ammonium sulfate, it will be salted out and precipitated.

Flocculation
Adding 10 times the volume of ethanol, isopropanol or acetone to the agar solution can cause agar to flocculate and precipitate from the aqueous solution. As well, a salt solution of calcium sulphate, magnesium sulphate or ammonium sulphate solutions will salt out agar solutions. Thanks to this property, you can dehydrate agar gel during the agar extraction.

Gel Temperature Hysteresis
Agar gel is a gel that can be reversed in temperature. The gel will melt when hot and harden again when chilled and allowed to stand (which can be repeated again). The solidification point of agar solution is between 32°C and 43°C and the melting point of agar gel is between 75°C and 90°C.

The melting point is very high as compared to the solidification point, which is peculiar to agar. It is called "hysteresis phenomenon". The high hysteresis of agar explains many of its use advantages.

Viscosity
The viscosity of agar aqueous solution (sol) varies depending on the type of raw materials, the quality of raw materials, the conditions of extraction, the pH of the solution, the amount of inorganic salts, the concentration of agar during measurement, the temperature and the addition of electrolytes.

In the extraction process of industrial agar, due to the treatment of chemical reagents, it has been damaged to a certain extent, and its viscosity is low. In addition, the viscosity of agar will decrease significantly after the agar solution is treated with high temperature, electrolytes, inorganic acids or acidic salts.

Non-Acidic Degradation
A large number of viscosity, diffraction and gel strength experiments and studies have shown that pure dry agar is extremely stable and difficult to degrade at room temperature. However, if it contains impurities, is at high temperature, is affected by ultrasound, strong gamma rays, strong stirring and other factors, it will cause the agar molecular chain to break and degrade, making some physical and chemical properties of agar worse.

Gelation
The biggest feature of agar is that it has gel properties. Even a 0.004% agar solution can form a gel at room temperature. Compared with other substances that can form a gel, its gel strength is the highest at the same concentration. When agar forms a gel, no coagulant is required.

Clarity and Inertness
Agar gel is highly transparent, and biological samples and chemical reactions can be easily observed. In addition, thanks to its chemical inertness, it is compatible with a variety of substances and organisms.

Created: 21 Mar 2025 06:03:32 AM