Sodium carboxyme thyl cellulose (CMC), a carboxymethylated derivative of cellulose, also known as cellulose gum, is the most dominant ionic cellulose gum.

CMC is usually an anionic polymer compound made by reacting natural cellulose with caustic soda and monochloroacetic acid, and the molecular weight of the compound ranges from a few thousand to a million. The unit structure of the molecule is shown in Figure 1.
CMC belongs to the modification of natural cellulose, and now the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) have officially called it “modified cellulose”. The synthesis method of sodium carboxymethyl cellulose was invented by German E. Jansen in 1918 and patented in 1921, and has been commercially produced in Europe since then.

CMC was only a crude product, used as a colloid and binder. 1936-1941, sodium carboxymethyl cellulose industrial application research is quite active, published a few quite inspiring patents, during the Second World War, Germany will be used in synthetic detergents as an anti-redeposition agent, and as a substitute for some natural gums (such as gelatin, gum arabic), so that the CMC industry has been greatly developed. The CMC industry has been greatly developed.

The American Hercules Company started the industrial production of CMC in 1943 and produced refined sodium carboxymethyl cellulose in 1946, which was recognized as a safe food additive.

CMC has many special properties, such as thickening, bonding, film-forming, water-holding, emulsification, suspension, etc., and its non-toxic, odorless, not easy to ferment, good thermal stability and other characteristics are widely used in petroleum, geology, daily chemicals, food, medicine and other industries, known as “industrial monosodium glutamate”.

Structural Characteristics of CMC

CMC is white or yellowish powder, granular or fibrous solid, it is a kind of macromolecular chemical substance, it can absorb water and swell, it can form transparent viscous gel when it is dissolved in water, and the pH value of water suspension is 6.5-8.5, it is insoluble in organic solvents, such as ethanol, ether, acetone, and chloroform, etc. Solid CMC has good thermal stability, and it is widely used in petroleum and geological industries, food and chemical industries, and pharmaceutical industries.

Solid CMC is more stable to light and room temperature, and can be stored for a long time in a dry environment.CMC is a kind of cellulose ether, which is usually made from short cotton lint (the cellulose content is up to 98%) or wood pulp, and then reacted with sodium monochloroacetate after treatment with sodium hydroxide, and the molecular weight of the compound is 6400 (±1000). There are usually two methods of preparation: the hydrocoal method and the solvent method. Other plant fibers are also used to prepare CMC.

Functional properties and applications

CMC is not only a good emulsion stabilizer and thickener in food applications, but also has excellent freezing and melting stability, and can improve the flavor of the product and extend the storage time.

In 1974, the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) approved the use of pure CMC in food after rigorous biological and toxicological studies and tests, and the safe intake (ADI) of the international standard is 25mg/kg body weight/day.

1. Thickening and emulsification stability
Consumption of CMC can have an emulsion stabilizing effect on beverages containing fatty proteins. This is because CMC dissolved in water becomes a transparent stable colloid, protein particles in the colloid membrane under the protection of the particles with the same charge, it can make protein particles in a stable state. It also has a certain emulsifying effect, so at the same time can reduce the surface tension between fat and water, so that the fat is fully emulsified.

CMC can improve the stability of the product, this is because when the pH value of the product deviates from the isoelectric point of the protein, sodium carboxymethylcellulose can form a composite structure with the protein, and this structure can make the stability of the product improve.

2. Improve puffiness
CMC used in ice cream, can improve the expansion of ice cream, improve the melting speed, give a good shape and taste, and can control the size and growth of ice crystals during transportation and storage, the amount of use according to the total amount of 0.5% of the ratio added.

This is because CMC has good water retention, dispersion, the protein particles in the colloid, fat balls, water molecules organically combined to form a uniform and stable system.

3. Hydrophilicity and rehydration
This functional property of CMC is generally used in bread production, which can make the honeycomb uniform, increase the volume, reduce the dregs, and at the same time, it also has the function of heat preservation; add CMC noodles with good water holding capacity, boiled resistance and good taste.

This is determined by the molecular structure of CMC, it is a cellulose derivative, there are a large number of hydrophilic groups in the molecular chain: -OH group, -COONa group, so CMC has a better hydrophilicity and water retention than cellulose.

4.Gelation
Thixotropic CMC refers to the macromolecular chain has a certain number of interactions, tends to form a three-dimensional structure, after the formation of three-dimensional structure, the solution viscosity performance increases, after breaking the three-dimensional structure, the viscosity performance decreases, thixotropic phenomenon is the apparent viscosity change dependent on time. CMC with thixotropy has an important role in gelling system, can be used to make jelly, jam and other foods.

5. It can be used as clarifying agent, foam stabilizer, and increase taste
CMC can be used in the production of alcohol, so that the taste is more mellow, rich, long aftertaste; in the production of beer can be used as a foam stabilizer, so that the foam is rich and long-lasting, improve the taste.

CMC is a kind of polyelectrolyte, which may be involved in the reaction of maintaining the balance of various types of wine body in wine, and at the same time, it also combines with the already formed crystals and changes the structure of the crystals, so that the conditions of the crystals’ existence in the wine are changed and the aggregation of precipitates is caused.