Views: 1 Author: Site Editor Publish Time: 2023-06-13 Origin: Site
Microbial polysaccharides are polysaccharides secreted by microorganisms (fungi, bacteria, cyanobacteria, etc.) during the growth process to protect them from external damage. Microbial polysaccharides exist in the form of cell wall polysaccharides, intracellular polysaccharides, and extracellular polysaccharides. Xanthan gum refers to: Xanthomonas spp. takes carbohydrates such as glucose, corn starch and sucrose as carbon source and soy flour as nitrogen source, and produces a widely used, water-soluble, high-viscosity extracellular polysaccharide through biofermentation and refining extraction.The unique structure of xanthan gum molecule gives it excellent rheological properties, good viscosity, acid and alkali resistance, pseudoplasticity and high temperature resistance, resistance to high concentrations of salt, emulsification and suspension properties, as stabilizers, thickeners, emulsifiers, suspending agents, lubricants, film-forming agents and adhesives, etc. It is widely used in more than 20 industries such as food, medicine, petroleum, textile, foundry and chemical industry, and is the biopolysaccharide with the largest production scale and extremely wide range of uses.
According to the application area, it is mainly divided into industrial grade xanthan gum, food grade xanthan gum, cosmetic grade xanthan gum, pharmaceutical grade xanthan gum and oil drilling grade xanthan gum.
Xanthan gum is usually added to other products as an auxiliary material, its main role is to adjust the viscosity of the product to improve product stability and performance. Viscosity is an important indicator to measure the physical and chemical properties and performance of xanthan gum products, in different application industries and fields, the viscosity requirements of xanthan gum products are different.
The final viscosity of xanthan gum products is closely related to the yield and purity of xanthan gum in the preparation process: research shows that in the strain selection stage, the higher yield of xanthan gum can be obtained by mutagenesis selection compared with the native strain; in the fermentation stage, the viscosity of the fermentation broth and the yield of xanthan gum can be significantly improved by optimizing the fermentation process, improving the types and concentrations of carbon and nitrogen sources in the medium, and the components and contents of inorganic salts; in the purification stage of the fermentation broth, the salt-alcohol precipitation method can significantly improve the precipitation and separation efficiency of xanthan gum and obtain higher product purity than the alcohol precipitation method.
During the use of xanthan gum products, the concentration of xanthan gum, solution pH, mineralization and temperature can have different effects on the apparent viscosity and rheological properties of xanthan gum solutions. Therefore, the production process can be optimized and the conditions of use can be controlled to obtain the appropriate viscosity and rheological properties for different applications in different industries.
A DV2T standard viscometer with SSA small volume sample adapter (shown in Figure 1) was used to measure the viscosity change of a xanthan gum at different concentrations and under different shear conditions.
TC-650 AP water bath circulation system is used to control the sample temperature (testing temperature is 25℃), Rheocalc T software is connected to the mainframe for program editing and data acquisition, and to plot the viscosity change curve. A certain amount of xanthan gum solution with concentrations of 0.4%, 0.6%, 0.8% and 1.0% was drawn into the sample cup of SSA, the rotor was slowly submerged into the sample, and then the viscometer mainframe and TC-650 AP water bath circulation system were connected. Edit the test program on the Rheocalc T software, set the rotor speed gradient to 10-60 RPM, and start measurement after the sample temperature stabilizes.
Figure 2 Viscosity change curve of xanthan gum solution with different concentrations
According to the test results in Figure 2, it can be seen that at the same shear rate, the viscosity of xanthan gum solution increases significantly with the increase of the solution concentration. At a certain concentration, the viscosity of the solution decreases with the increase of shear rate, showing pseudoplastic fluid properties; as the concentration of the solution increases, the greater the effect of shear rate on the viscosity of the solution, the more obvious the phenomenon of shear thinning.
Xanthan gum is a biological polymer, its polysaccharide molecules through hydrogen bonding, electrostatic gravitational force and other effects to form an orderly system, mutual entanglement, and therefore a great viscous resistance to flow, with the increase in shear force, will make the flow of the entanglement point dissolved, the polymerization structure state deconfluence into irregular nematic state so that the viscosity drops rapidly, showing the shear thinning pseudoplastic phenomenon.
The sample volume required for SSA testing is only 2-16 mL (the exact sample volume depends on the rotor type used), which can effectively save testing costs and improve testing efficiency; SSA uses a coaxial cylindrical rotor and accompanying sample cups, allowing calculation of shear rate and shear stress to obtain absolute viscosity;The TC series circulating water bath system has a temperature control accuracy of up to 0.01℃, providing accurate and stable temperature conditions for viscosity testing.