Structure

Xanthan gum molecules are composed of D-glucose, D-mannose, D-glucuronic acid, acetyl and pyruvic acid, with a relative molecular mass between 2×106 and 5×107. Its primary structure is composed of a glucosyl main chain connected by β-(1→4) bonds and a side chain of a trisaccharide unit; its side bonds are formed by alternating D-mannose and D-glucuronic acid, with a molecular ratio of 2:1; the trisaccharide side chain is connected to the main chain by an α-(1→3) chain with an acetyl group at the C6 position, and pyruvic acid is carried in the form of an acetal on the D-mannose residue at the end of the side chain. Its higher-order structure is that the side chain and the main chain are maintained by hydrogen bonds to form a helix and multiple helix.

The secondary structure of xanthan gum is that the side chain is reversely wound around the main chain skeleton, and the rod-shaped double helix structure is maintained by hydrogen bonds. The tertiary structure of xanthan gum is a helical complex formed by weak non-covalent bonds between the rod-shaped double helix structures.

Performance

Xanthan gum is the most superior biological gum in the world, integrating thickening, suspension, emulsification and stabilization. The amount of pyruvic acid groups at the end of the molecular side chain of xanthan gum has a great influence on its performance. Xanthan gum has the general properties of long-chain polymers, but it contains more functional groups than general polymers, and will show unique properties under specific conditions. Its conformation in aqueous solution is diverse, and it exhibits different characteristics under different conditions.

Suspension and emulsification

Xanthan gum has a good suspension effect on insoluble solids and oil droplets. Xanthan gum sol molecules can form super-bonded ribbon-like spiral copolymers, forming a fragile mesh structure similar to glue, so it can support the morphology of solid particles, droplets and bubbles, showing a strong emulsification stabilization effect and high suspension ability.

Water solubility

Xanthan gum can dissolve quickly in water and has good water solubility. It can also dissolve in cold water, which can save complicated processing and is easy to use. However, due to its strong hydrophilicity, if it is added directly to water without sufficient stirring, the outer layer will absorb water and swell into micelles, which will prevent water from entering the inner layer, thus affecting the effect. Therefore, it is necessary to pay attention to correct use. Xanthan gum dry powder or dry powder auxiliary materials such as salt and sugar are mixed well and then slowly added to the stirring water to make a solution for use.

Thickening

Xanthan gum solution has the characteristics of high viscosity at low concentration (the viscosity of 1% aqueous solution is equivalent to 100 times that of gelatin), and is an efficient thickener.

Pseudoplasticity

Xanthan gum aqueous solution has high viscosity under static or low shear, and shows a sharp drop in viscosity under high shear, but the molecular structure remains unchanged. When the shear force is eliminated, the original viscosity is immediately restored. The relationship between shear force and viscosity is completely plastic. Xanthan gum has very prominent pseudoplasticity, which is extremely effective in stabilizing suspensions and emulsions.

Stability to heat

The viscosity of xanthan gum solution does not change much with temperature. The viscosity of general polysaccharides changes due to heating, but the viscosity of xanthan gum aqueous solution hardly changes between 10-80℃. Even low-concentration aqueous solution still shows stable high viscosity in a wide temperature range. 1% xanthan gum solution (containing 1% potassium chloride) is heated from 25℃ to 120℃. Its viscosity only decreases by 3%.

Stability to acid and alkali

Xanthan gum solution is very stable to acid and alkali. Its viscosity is not affected between pH 5-10. The viscosity changes slightly when the pH is less than 4 and greater than 11. In the pH range of 3-11, the maximum and minimum viscosity values differ by less than 10%. Xanthan gum can be dissolved in a variety of acid solutions, such as 5% sulfuric acid, 5% nitric acid, 5% acetic acid, 10% hydrochloric acid and 25% phosphoric acid, and these xanthan gum acid solutions are quite stable at room temperature, and their properties will not change for several months. Xanthan gum can also be dissolved in sodium hydroxide solution and has thickening properties. The solution formed is very stable at room temperature. Xanthan gum can be degraded by strong oxidants such as perchloric acid and persulfate, and the degradation is accelerated as the temperature rises.

Stability to salt

Xanthan gum solution can be miscible with many salt solutions (potassium salt, sodium salt, calcium salt, magnesium salt, etc.), and the viscosity is not affected. Under high salt concentration conditions, even in saturated salt solutions, it still maintains its solubility without precipitation and flocculation, and its viscosity is almost unaffected.

Stability to enzymatic reactions

The stable double helix structure of xanthan gum makes it extremely antioxidant and anti-enzymatic. Many enzymes such as proteases, amylases, cellulases and hemicellulases cannot degrade xanthan gum.