What do you know about sodium alginate?

Editor:Sodium alginate　　　　Source:Sodium alginate manufacturer　　　　2017-05-28 14:50

Sodium alginate is a by-product after extracting iodine and mannitol from kelp or Sargassum of brown algae, and its molecule is composed of β -D- mannuronic acid (β -D-mannuronic, m) and α -L- guluronic acid (α -l -L-guluronic, g) press (1→ 4) key connection, which is a kind ofNatural polysaccharideIt has the stability, solubility, viscosity and safety required by pharmaceutical excipients. Sodium alginate has been widely used in food industry and medicine.
　　　　Sodium alginate is derived frombrown algagenerickelporsea grapeMiddle extractioniodineandmannitolSubsequentby-productIts molecule consists of β -D- mannuronic acid (β -D-mannuronic, m) and α -L- guluronic acid (α -l -L-guluronic, g) press (1→ 4) key connection. The aqueous solution of sodium alginate has high viscosity and has been used as food.Thickener、stabilizing agent、emulgatorWait. Sodium alginate is a non-toxic food, which was included in the United States Pharmacopoeia as early as 1938. Sodium alginate contains a lot of — COO－-,which can show polyanionic behavior in aqueous solution and has certain adhesion, can be used as a drug carrier for treating mucosal tissues. Under acidic conditions, — COO－-into — COOH，ionization degreeWhen decreasing, the hydrophilicity of sodium alginate decreases, the molecular chain shrinks and the pH value increases, — COOH group dissociates constantly, and the hydrophilicity of sodium alginate increases and the molecular chain stretches. Therefore, sodium alginate has obvious pH sensitivity. Sodium alginate can quickly form gel under extremely mild conditions, when Ca2+, Sr2+ and so on are present.cationWhen it exists, Na+ on G units reacts with divalent cations, and G units pile up to form cross-linked network structure, thus forming hydrogel. Sodium alginate formationgelMild conditions, which can avoid sensitive drugs, protein,cellandenzymeInactivation of such active substances. Because of these excellent characteristics, sodium alginate has been widely used in food industry and medicine.

Its mild sol-gel process and good biocompatibility make alginic acid suitable as microcapsules for releasing or embedding drugs, proteins and cells. When the carboxyl group at the 6 th position is combined with sodium ion, Sodium Alginate is formed. There are many classification methods of sodium alginate. Structurally, it can be divided into three types: high G/M ratio, medium G/M ratio and low G/M ratio. From the viscosity, it can be divided into low viscosity, medium viscosity and high viscosity sodium alginate. In terms of purity, it can be divided into three levels: industrial, edible and medical. Different qualities of sodium alginate have great influence on the structure of colloidal beads. Generally speaking, sodium alginate with high G/M ratio and low viscosity is suitable for preparing colloidal beads. Moreover, when the colloidal beads are applied to the field of bioengineering, medical grade sodium alginate should be selected.

　　manufacturing technique

　　The technological process of sodium alginate is as follows: dry or wet seaweed (algae) is crushed, washed with water to remove impurities, extracted with strong alkali water and clarified to obtain crude alginate solution, precipitated with calcium chloride to obtain colored calcium alginate, decolorized and deodorized, treated with acid to remove soluble impurities to obtain alginate precipitate, reacted with sodium carbonate to obtain sodium alginate, and then dried, crushed and sieved to obtain sodium alginate powder.

　　chemical property

　　compose

　　Sodium alginate (C6H7O8Na)n is mainly composed of the sodium salt of alginic acid, which is a copolymer composed of a-L- mannuronic acid (M unit) and b-D- guluronic acid (G unit) connected by 1,4- glycosidic bond and composed of different proportions of GM, MM and GG fragments.

　　molecular weight

　　The molecular weight of commercial sodium alginate is usually dispersed like polysaccharide. 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). These two are defined by the following formula:

　　Where Ni= the number of molecules with a specific molecular weight Mi, and Wi= the weight of molecules with a specific molecular weight Mi.

　　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.

　　structural formula

　　The molecular formula is (c6h7nao6) x.

　　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.

What are the unique features of sodium alginate in the food field?

Food-grade sodium alginate, a pure natural green food additive.

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