The main properties of sodium carboxymethyl cellulose, what are its uses and how to use it

01. Property and product introduction of sodium carboxymethyl cellulose

Sodium carboxymethyl cellulose (CMC) is a highly polymerized fiber ether made from natural cellulose by chemical modification. Its structure is mainly composed of D-glucose units β（ 1 → 4).

CMC is white or milk white fibrous powder or particle with density of 0.5-0.7g/cm3, almost odorless, tasteless and hygroscopic. It is easy to disperse in water to form transparent colloidal solution and insoluble in organic solvents such as ethanol. When the pH value of 1% aqueous solution is 6.5-8.5, the viscosity of the slurry decreases significantly when the pH value is more than 10 or less than 5, and the performance is the best when the pH value is 7. For thermal stability, the viscosity increases rapidly below 20 ℃ and changes slowly at 45 ℃. Long time heating above 80 ℃ can denature the colloid, but the viscosity and properties decrease obviously. It is soluble in water and transparent; It is very stable in alkaline solution, easy to hydrolyze in case of acid, precipitate when pH value is 2-3, and precipitate in case of multivalent metal salt.

Structural formula: c6h7 (OH) 2och2coona molecular formula: c8h11o5na

The main reaction is as follows: the natural cellulose firstly alkalizes with NaOH, and with the addition of chloroacetic acid, the hydrogen on the hydroxyl group of its glucose unit replaces the carboxymethyl group in chloroacetic acid. It can be seen from the structural formula that there are three hydroxyl groups on each glucose unit, namely C2, C3 and C6 hydroxyl groups. The degree of substitution of hydrogen on the hydroxyl group of glucose unit is expressed by the degree of substitution. If the hydrogen on the three hydroxyl groups of each unit is replaced by Carboxymethyl group, it is defined as the degree of substitution is 3. The degree of substitution of CMC directly affects the solubility, emulsification, thickening and viscosity of CMC Stability, acid resistance and salt resistance.

It is generally considered that the emulsifying property is better when the degree of substitution is about 0.6-0.7, and other properties are improved with the increase of the degree of substitution. When the degree of substitution is greater than 0.8, the acid and salt resistance of the emulsion is obviously enhanced.

In addition, it is also mentioned above that there are three hydroxyl groups on each unit, namely, the secondary hydroxyl group of C2 and C3 and the primary hydroxyl group of C6. Theoretically, the activity of the primary hydroxyl group is higher than that of the secondary hydroxyl group. However, according to the homologous effect of C, the - OH group on C2 is more acidic, especially in the strong alkali environment, its activity is stronger than that of C3 and C6, so it is more prone to substitution reaction, followed by C6, and C3 is the weakest.

In fact, the properties of CMC are not only related to the degree of substitution, but also to the distribution uniformity of carboxymethyl groups in the whole cellulose molecule and the substitution uniformity of hydroxymethyl groups with C2, C3 and C6 in each unit of each molecule. Because CMC is a highly polymerized linear compound, and its carboxymethyl group has the non-uniformity of substitution in the molecule, when the solution is still, the molecules have different orientations. When there is shear force in the solution, the long axis of the linear molecules has a tendency to turn to the flow direction, and this tendency becomes stronger with the increase of shear rate until the final orientation is completely arranged, This property of CMC is called pseudoplasticity. The pseudo plasticity of CMC is conducive to homogenization and pipeline transportation, which is not too greasy in liquid milk, and is conducive to the release of milk aroma..

The main reason for using CMC products is that we should have enough understanding of the main index parameters such as stability, viscosity, acid resistance and viscosity. We know how to choose the right product.

Low viscosity CMC products, refreshing taste, low viscosity, almost no thick feeling, mainly used in special sauces and beverages, health oral liquid is also a good choice.

Medium viscosity CMC products are mainly used in solid drinks, ordinary protein drinks and fruit juices. The specific selection depends on the personal habits of engineers. CMC contributes a lot to the stability of dairy products and beverages.

Compared with starch, guar gum, xanthan gum and other products, the stability of CMC is more obvious, especially in meat products, the water retention advantage of CMC is more obvious! CMC is also a good choice among stabilizers such as ice cream.

The main indexes of CMC quality are DS and purity. Generally, the properties of CMC are different with different DS; As the degree of substitution increases, the solubility increases, and the transparency and stability of the solution become better. It is reported that the transparency of CMC is better when the degree of substitution is 0.7-1.2, and the viscosity of CMC aqueous solution is the highest when the pH value is 6-9.

In order to ensure its quality, in addition to the selection of etherifying agent, some factors affecting the degree of substitution and purity must also be considered, such as the dosage relationship between alkali and etherifying agent, etherification time, water content of the system, temperature, DH value, solution concentration and salts, etc.

The quality of CMC products depends mainly on the solution of the product. If the product is clear, the gel particles are few, the free fibers are few, and the impurity spots are few. The quality of CMC is basically determined. If the solution is placed for a few days, the solution does not appear white or turbid, or very clear, that is a better product.

02. Dissolution and dispersion of CMC products

The CMC was mixed with water directly, and then the paste was prepared. When preparing CMC paste, first add a certain amount of clean water into the batching tank with stirring device. When the stirring device is turned on, slowly and evenly spread CMC into the batching tank and keep stirring, so that CMC and water can be completely integrated and CMC can be fully dissolved.

When dissolving CMC, the reason why it is necessary to evenly spread and continuously stir is "to prevent agglomeration, caking and reduce the amount of CMC dissolution when CMC meets with water", and to improve the dissolution rate of CMC. Generally speaking, the stirring time is much shorter than the time required for complete dissolution of CMC, and the time required for both depends on the specific situation.

The basis for determining the stirring time is: when CMC is evenly dispersed in water and there is no obvious large lumpy object, the stirring can be stopped, so that CMC and water can permeate and fuse with each other in the static state. The stirring speed is generally between 600-1300 revolutions, and the stirring time is generally controlled at about 1 hour.

There are several bases to determine the time required for complete dissolution of CMC

(1) CMC and water are completely bonded, and there is no solid-liquid separation between them;

(2) The mixed paste is uniform and smooth;

(3) The color of the mixed paste is nearly colorless and transparent, and there is no granular object in the paste. It takes 10-20 hours from the moment CMC is put into the batching tank and mixed with water to the moment CMC is completely dissolved. In order to produce fast and save time, homogenizer or colloid mill are widely used to disperse products.

03. Application characteristics and process requirements of CMC in food

CMC has many advantages over other food thickeners

1、 CMC is widely used in food and its characteristics

（1） CMC has good stability

In cold food such as popsicle and ice cream, the use of CMC can control the formation of ice crystals, improve the expansion rate, maintain uniform structure, resist melting, taste delicate and smooth, and whiten the color. In dairy products, whether it is seasoning milk, fruit milk or yogurt, it can react with protein in the range of pH isoelectric point (PH4.6) to form a complex structure complex, which is conducive to the stability of the emulsion and the improvement of protein impedance.

（2） CMC can be compounded with other stabilizers and emulsifiers.

In food and beverage products, general manufacturers use a variety of stabilizers, such as xanthan gum, guar gum, carrageenan, dextrin, emulsifiers such as monostearate glyceride, sucrose fatty acid ester, etc. It can make the advantages complement each other, play the role of synergy and reduce the production cost.

（3） CMC is pseudoplastic

The viscosity of CMC is reversible at different temperatures. The solution viscosity decreases with the increase of temperature, and vice versa; In the presence of shear force, the viscosity of CMC decreases, and with the increase of shear force, the viscosity decreases. These properties of CMC can reduce the equipment load and improve the homogenization efficiency in the process of mixing, homogenizing and pipeline transportation, which is incomparable with other stabilizers.

2、 Process requirements

CMC as an effective stabilizer, if used improperly, it will affect the use effect, and even lead to product scrap. Therefore, for CMC, it is very important to disperse the solution sufficiently and evenly to improve the efficiency, reduce the dosage, improve the product quality and increase the yield. This requires us all food manufacturers to fully understand the characteristics of various raw materials, reasonably adjust their production process, so that CMC can give full play to its role, especially in each process stage

（1） Ingredients

1. High speed shear dispersion method with mechanical force: all equipment with mixing ability can be used to assist CMC to disperse in water. Through high speed shear, CMC can be evenly soaked in water and CMC dissolution can be accelerated. At present, some manufacturers use water powder mixer or high-speed mixing cylinder.

2. Dry mixing and dispersing method of granulated sugar: mix CMC and granulated sugar in the ratio of 1:5, and sprinkle them slowly under constant stirring to make CMC dissolve fully.

3. Dissolving CMC with saturated sugar water, such as maltose, can accelerate the dissolution of CMC.

（2） Acid addition

For some acidic drinks, such as yogurt, acid resistant products should be selected. If they are operated normally, the product quality can be improved, and the phenomenon of product precipitation and stratification can be prevented.

1. When adding acid, the temperature should be strictly controlled, generally less than 20 ℃.

2. The acid concentration should be controlled at 8-20%, the lower the better.

3. Add acid by spraying, add along the tangent direction of the container, generally 1-3min.

4. Slurry speed n = 1400-2400r / M

（3） Homogenization

1. Emulsification purpose.

Homogenization: for fat containing liquid, CMC should be mixed with emulsifier, such as monoglyceride, homogenization pressure 18-25mpa, temperature 60-70 ℃.

2. Disperse the purpose.

Homogenization, for the early various ingredients, if not completely uniform, there are still some small particles, must be homogenized, homogenization pressure 10MPa, temperature 60-70 ℃.

（4） Sterilization

When CMC is at high temperature, especially when it is higher than 50 ℃ for a long time, the viscosity of CMC with poor quality will decrease irreversibly. Generally, the viscosity of CMC from manufacturers will decrease seriously when it is at 80 ℃ for 30 minutes. Therefore, instantaneous sterilization or pasteurization can be used to shorten the time of CMC at high temperature.

（5） Other considerations

1. The selected water quality should use clean treated tap water instead of well water to avoid microbial infection and affect product quality.

2. The utensils for dissolving and holding CMC can not be metal containers, but stainless steel containers or wooden basins or ceramic containers. Prevent the penetration of divalent metal ions.

3. After each use of CMC, the mouth of the packaging bag should be tied tightly to prevent CMC from moisture absorption and deterioration.

04. Questions and answers in the use of CMC

1、 Question: how can low viscosity, medium viscosity and high viscosity be distinguished from each other in terms of structure and consistency?

answer:

It is understood that the length of molecular chain is different, or the molecular weight is different, which can be divided into low viscosity, medium viscosity and high viscosity. In the macro performance, of course, the corresponding viscosity is different, the same concentration, the viscosity is high or low, and the stability of the product is not directly related to the acid ratio. It mainly depends on the solution of the product.

2、 Question: what are the specific performance of products with substitution degree above 1.15, or the higher the substitution degree is, the better the specific performance of products is.

answer:

The products with the same viscosity have higher degree of substitution and smoother feeling. The solution of products with high degree of substitution is glossy, while that of products with general degree of substitution is white.

3、 Question: do you choose medium viscosity to make fermented protein drinks?

answer:

Low viscosity products, substitution degree about 0.90, acid resistance better products.

4、 Question: how can CMC dissolve quickly? Sometimes I use it. It boils, but it dissolves slowly.

answer:

Mix with other colloids, or disperse with 1000-1200 speed agitator. The dispersion of CMC is not good, hydrophilicity is good, easy to agglomerate, high degree of substitution products are more obvious! The dissolving speed of warm water is faster than that of cold water. Boiling is generally not recommended. Long time cooking of CMC products will destroy the molecular structure, and the products will lose viscosity!

05. Application examples of CMC in acid milk beverage

1、 Theoretical basis

It can be seen from the structural formula that the hydrogen (Na +) on CMC is very easy to be dissociated in aqueous solution (generally in the form of sodium salt), so CMC exists in the form of anion in aqueous solution, that is, it shows negative charge. When the pH of amphoteric protein is less than the isoelectric point, its ability to combine - COO group of protons is much greater than that of - NH3 + group giving protons, which shows positive charge, In the milk, 80% of the protein is casein, and the isoelectric point of casein is about 4.6. The pH of general acidic milk drinks is 3.8-4.2. Therefore, CMC and milk protein can form a relatively stable structure by charge absorption under acidic conditions, and form a protective film around the protein. This property of CMC is called microcapsule embedding binding property.

2、 Recommended formula of acid milk beverage

（1） Basic formula of formulated acid milk beverage (1000kg)

Fresh milk (whole milk powder) 350 (33) kg

Sugar 50kg

Compound sweetener (50 times) 0.9kg

CMC3.5～6Kg

Monoglyceride 0.35kg

Sodium citrate 0.8kg

Citric acid 3kg

Lactic acid (80%) 1.5kg

Note:

1) Milk powder can be replaced by partially hydrolyzed protein to control protein content more than 1%.

2) The final acidity of the product should be controlled between 50 and 60 ° About t.

3) The soluble solid content was 7.5% - 12%.

（2） Formula of lactic acid bacteria beverage (1000kg)

Fermented milk 350-600kg

Sugar 60kg

Compound sweetener (50 times) 1kg

CMC3.2～8Kg

Monoglyceride 0.35kg

Sodium citrate 1kg

Citric acid

Note: adjust the acidity of milk with citric acid, and the final acidity of the product should be controlled at 60 ~ 70 ° About t.

3、 Key points of CMC selection

Fh9 and fh9 extra high (fvh9) are generally selected as blended yoghurt drinks. Fh9 has a thick taste, and the addition amount is 0.35% - 0.5%. Fh9 extra high is more refreshing, and the effect of blending is good, and the addition amount is 0.33% - 0.45%.

Generally, fl100, FM9 and fh9 are selected for lactic acid bacteria beverage (special process production), and fl100 is generally used for taste