Detailed Guide: What is CMC and How Does It Apply to Products

What is CMC? Carboxymethyl cellulose sodium, commonly known as CMC, is a high-polymer cellulose ether obtained by chemically modifying natural cellulose. Its structure mainly consists of D-glucose units linked by β(1→4) glycosidic bonds.

Introduction - What is CMC?

CMC appears as a white or milky-white fibrous powder or granule with a density of 0.5-0.7 g/cubic centimeter. It is almost odorless, tasteless, and hygroscopic. CMC can be easily dispersed in water to form a transparent gel-like solution, but it is insoluble in organic solvents such as ethanol. The pH of a 1% aqueous solution ranges from 6.5 to 8.5, and the viscosity of the gel significantly decreases when the pH is greater than 10 or less than 5. The best performance is achieved when the pH is at 7.

Also, CMC is thermally stable, and its viscosity increases rapidly below 20°C, changes slowly at 45°C, and significantly decreases at temperatures above 80°C due to the denaturation of its colloidal properties. It is soluble in water, forming a transparent solution. CMC is stable in alkaline solutions but can be hydrolyzed by acids, leading to precipitation at a pH of 2-3. It can also react with multivalent metal salts and form precipitates.

The molecular formula of CMC: C₈H₁₁O₅Na

The structural formula: C₆H₇(OH)₂OCH₂COONa.

The main reaction of CMC is the alkalization reaction of natural cellulose with NaOH, followed by the substitution reaction of the hydrogen on the hydroxyl group of the glucose unit with the carboxymethyl group in the chloroacetic acid. From the structure, it can be seen that there are three hydroxyl groups on each glucose unit, namely the C2, C3, and C6 hydroxyl groups.  

The degree of substitution indicates the extent to which the hydrogen on the hydroxyl group of the glucose unit is replaced by the carboxymethyl group. When all three hydroxyl groups on each unit are substituted, the degree of substitution is defined as 3. The degree of substitution of CMC directly affects its solubility, emulsifying properties, thickening properties, stability, acid resistance, and salt resistance.

It is generally believed that emulsifying properties are better when the degree of substitution is around 0.6-0.7, and other properties are correspondingly improved as the degree of substitution increases. When the degree of substitution is greater than 0.8, its acid resistance and salt resistance are significantly enhanced.

In addition, it was mentioned above that each unit has three hydroxyl groups, namely the C2 and C3 secondary hydroxyl groups and the C6 primary hydroxyl group. Theoretically, the activity of the primary hydroxyl group is greater than that of the secondary hydroxyl group, but according to the isotopic effect of carbon, the -OH group on C2 is more acidic, especially in a strongly alkaline environment, its activity is stronger than that of C3 and C6, so it is more prone to substitution reactions. C6 is second, and C3 is the weakest.

How Does It Apply to Products?

To use CMC products, it is important for us to have a sufficient understanding of the main parameters such as stability, viscosity, acid resistance, and so on. This will help us to choose the most suitable product.

Low viscosity CMC products are refreshing, low in viscosity, and have almost no thickness. They are mainly used in special sauces, beverages, and health drinks.

Medium viscosity CMC products are mainly used in solid beverages, ordinary protein drinks, and juices. The specific choice depends on the personal preferences of the engineer. CMC also contributes significantly to the stability of dairy beverages.

High viscosity CMC products have a wide range of applications and are comparable to starch, guar gum, and xanthan gum. CMC stability is particularly evident in meat products, where its water retention advantage is more apparent. CMC is also a good choice for stabilizers in ice cream and other products.

The main indicators for measuring the quality of CMC are the degree of substitution (DS) and purity. Different DS values result in different properties of CMC. As the degree of substitution increases, the solubility, transparency, and stability of the solution improve. It has been reported that the best transparency of CMC is achieved at a degree of substitution of 0.7-1.2, and the maximum viscosity of the water solution is obtained at a pH value of 6-9.

To ensure its quality, in addition to selecting etherifying agents, it is also necessary to consider factors that affect the degree of substitution and purity, such as the amount ratio of alkali to etherifying agent, etherification time, the water content of the system, temperature, DH value, solution concentration, and salt content.

Summary

In short, knowing “what is CMC” for your specific needs can make all the difference in achieving the perfect texture and stability for your food and beverage creations. So, whether you're whipping up a refreshing juice, a hearty stew, or a sweet treat like ice cream, CMC can help you achieve your culinary dreams!