Analysis of physicochemical properties of sodium alginate by Nanshan biologists

compose

　　Sodium alginate (CHONa) is mainly composed of sodium salt of alginic acid, which consists of α -L- mannuronic acid (M unit) and β -D- guluronic acid (G unit) depends on β Copolymers linked by -1,4- glycosidic bonds and composed of different proportions of GM, MM and GG fragments.
　

　　The molecular weight of commercial sodium alginate is usually like polysaccharide.

　　Same, more scattered. Therefore, the molecular weight of a sodium alginate usually represents the average value of all molecules in this group. The most common ways to express molecular weight are number average molecular weight (Mn) and weight average molecular weight (Mw).

　　In a polydisperse molecular group, MW is usually > Mn. The coefficient of Mw/Mn is dispersion index, and the index of sodium alginate commodity is in the classical range of 1.5 ~ 2.5. The most commonly used method to determine molecular weight is based on intrinsic viscosity and light scattering measurement.
　

　　Molecular formula of sodium alginate

　　The molecular formula of sodium alginate is (CHNaO)x, and its molecular structure is shown in the figure above.
　

　　pH value

　　Sodium alginate is slightly soluble in water and insoluble in most organic solvents. It is soluble in alkaline solution, which makes the solution sticky. Sodium alginate powder becomes wet when it meets water, and the hydration of particles makes its surface sticky. Then the particles quickly stick together to form a lump, which is slowly completely hydrated and dissolved. If the water contains other compounds that compete with alginate for hydration, sodium alginate is more difficult to dissolve in water. Sugar, starch or protein in water will reduce the hydration rate of sodium alginate, so it is necessary to prolong the mixing time. Salts of monovalent cations (such as NaCl) have similar effects when the concentration is higher than 0.5%. The pH value of sodium alginate in 1% distilled water solution is about 7.2.

　　stability

　　Sodium alginate has hygroscopicity, and the amount of water in equilibrium depends on relative humidity. The dried sodium alginate is quite stable in a well-sealed container at 25℃ and below. Sodium alginate solution is stable at pH 5 ~ 9. The degree of polymerization (DP) and molecular weight are directly related to the viscosity of sodium alginate solution, and the decrease of viscosity during storage can be used to measure the degree of depolymerization of sodium alginate. The stability of sodium alginate with high polymerization degree is not as good as that of sodium alginate with low polymerization degree. It is reported that sodium alginate can be hydrolyzed by proton catalysis, which depends on time, pH and temperature. Propylene glycol alginate solution is stable at room temperature and pH 3 ~ 4. When the pH is less than 2 or greater than 6, the viscosity will quickly decrease even at room temperature.
　

　　Physical properties of sodium alginate;
　

　　Sodium alginate system β Polymer of anhydrous sodium D-mannanate.

　　1. Form

　　Sodium alginate is white or yellowish powder, almost odorless and tasteless.

　　4. solubility

　　Sodium alginate is soluble in water and insoluble in organic solvents such as ethanol, ether and chloroform. Dissolve in water to form viscous liquid, and the pH value of 1% aqueous solution is 6-8. When pH=6-9, the viscosity is stable, and when heated above 80℃, the viscosity decreases.

　　3. Toxicity

　　Sodium alginate is non-toxic, with LD50>5000mg/kg.

　　4. Gelatinity

　　Effect of Chelating Agent on the Properties of Sodium Alginate Solution Chelating agent can complex divalent ions in the system, so that sodium alginate can be stabilized in the system.

　　5 Thickening property and film-forming property

　　(1) As a thickener for beverages/dairy products, sodium alginate has unique advantages in thickening: the good fluidity of sodium alginate makes the added beverage taste smooth; And can prevent the phenomenon of viscosity reduction in the product disinfection process. When sodium alginate is used as thickener, products with high molecular weight should be used as much as possible, and appropriate amount of Ca should be added. Can greatly improve the viscosity of sodium alginate.

　　(2) As a stabilizer for cold drinks such as ice cream, sodium alginate is a high-grade stabilizer, which can make cold drinks such as ice cream have a smooth appearance and a smooth taste. Because calcium alginate can form a stable thermal irreversible gel, it will not become coarse (ice crystal growth) during transportation and storage, and ice cream will not be deformed due to temperature fluctuation; At the same time, this ice cream has no peculiar smell when eaten, which not only improves the expansion rate but also improves the melting point, so that the quality and benefit of the product are significantly improved. The product tastes smooth, delicate and good. The addition amount is low, generally 1-mdash; 3‰ , the amount added abroad is 5-mdash; 10‰ .

　　(3) Frozen milk stabilized with sodium alginate as a stabilizer for dairy products and beverages has a good taste, no sticky and stiff feeling, sticky when stirring, and a sense of hysteresis.