Xanthan gum, also known as yellow gum and Han Sheng gum, is a kind of extracellular acidic heteropolysaccharide produced by the fermentation of Xanomonas bacteria. It is a polysaccharide polymer compound composed of D-glucose, D-mannose and D-glucuronic acid according to 2:2:1, with a relative molecular weight of more than 1 million. The secondary structure of xanthan gum is that the side chain is reversed wound around the main chain skeleton, and the rod-like double helix structure is formed through hydrogen bonding
character
Xanthan gum is light yellow to white movable powder, slightly smelly. Soluble in cold and hot water, neutral solution, resistant to freezing and thawing, insoluble in ethanol. When dispersed with water, it emulsifies into a stable hydrophilic viscous colloid
Characteristic performance
Xanthan gum is currently a combination of thickening, suspension, emulsification and stabilization in one. Superior performance of biological glue. The number of pyruvate groups in the end of the molecular side chain of xanthan gum has a great influence on its properties. Xanthan gum has the general properties of long chain polymers, but it contains more functional groups than ordinary polymers, and will show unique properties under certain conditions. Its conformation in aqueous solution is diverse and does not show different characteristics under conditions.
1. Suspension and emulsification
Xanthan gum has good suspension effect on insoluble solids and oil droplets. Xanthan colloidal molecules can form superbinding ribbon helical copolymers, forming a fragile glue-like network structure, so it can support the form of solid particles, droplets and bubbles, showing strong emulsifying stability and high suspension capacity.
2. Good water solubility
Xanthan gum dissolves quickly in water and has good water solubility. Especially in cold water can also be dissolved, can save complicated processing process, easy to use. However, because it has a strong hydrophilicity, if it is directly added to water and stirred insufficiently, the outer layer absorbs water and expands into micelles, which will prevent water from entering the inner layer, thus affecting the play of the role, so it must pay attention to the correct use. Xanthan gum dry powder or salt, sugar and other dry powder accessories mix well, slowly add to the stirring water feed, make a solution for use.
3. Thickening
Xanthan gum solution has the characteristics of low concentration and high viscosity (the viscosity of 1% aqueous solution is equivalent to 100 times that of gelatin), and is a thickening agent.
4. False plasticity
Xanthan glue solution has high viscosity under static or low shear action, and shows a sharp decrease in viscosity under high shear action, but the molecular structure is unchanged. When the shear force is applied, the original viscosity is immediately restored. The relationship between shear force and viscosity is completely malleable. Xanthan gum is very prominent in pseudoplasticity, which is very effective in stabilizing suspension and emulsion.
5. Stability to heat
The viscosity of xanthan gum solution does not change greatly with the change of temperature, the general polysaccharide will change viscosity due to heating, but the viscosity of the xanthan gum solution is almost unchanged between 10-80 ℃, even if the low concentration of the water solution still shows a stable high viscosity over a wide temperature range. 1% xanthan gum solution (containing 1% potassium chloride) is heated from 25 ° C to 120 ° C. Its viscosity is reduced by only 3%.
6. Stability of acid and base
Xanthan gum solution is very stable to acid and base, and its viscosity is not affected between PH 5-10, and the viscosity changes slightly when PH is less than 4 and greater than 11. In the PH3-11 range, the viscosity value varies by less than 10%. Xanthan gum can dissolve in a variety of acid solutions, and these xanthan acid solutions are quite stable at room temperature, and the quality of the products will not change for several months. Xanthan gum can also dissolve in sodium hydroxide solution, and has thickening properties. The resulting solution is stable at room temperature. Xanthan gum can be degraded by strong oxidants, such as perchloric acid and persulfuric acid, and degradation accelerates with increasing temperature.
7. Stability of 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 the condition of higher salt concentration, even in saturated salt solution, it still maintains its solubility without precipitation and flocculation, and its viscosity is almost unaffected.
8. Stability of enzymatic reaction
The stable double helix structure of xanthan gum makes it highly resistant to oxidation and enzymatic hydrolysis. Many enzymes, such as protease, amylase, cellulase and hemicellulase, cannot degrade xanthan gum.
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