SODIUM CARBOXYMETHYL CELLULOSE

Chemistry, Functionality, and Applications

Andrew C. HoeflerFood Ingredients Group, Hercules Incorporated

Wilmington, Delaware 19808

http://www.herc.com/foodgums/index.htm

2

Figure 1 is a diagrammatic representation of a cellulose molecule. Note that each glucose unit inthe cellulose chain has three hydroxyl groups, each of which is capable of hydrogen bonding to anadjacent molecule. In the bottom of Figure 1, we indicate cellulose more pictorially as a series ofcircles connected together in a long, linear chain.

Figure 2 shows a group of cellulose molecules in water. Because of the abundance of hydroxylgroups, and their ability to hydrogen bond to a neighboring molecule, the chains are bound tightlytogether. Water molecules, at any temperature, cannot force their way in between the chains tohydrate them, thus cellulose is water insoluble ( which is just as well, since most of our houses aremade of wood. I certainly would not want my house to dissolve the next time it rains! )

Figure 3 illustrates the reaction for the manufacture of CMC. It is essentially a two step process. Inthe first step, cellulose is suspended in alkali to open the bound cellulose chains, allowing water toenter. Once this happens, the cellulose is then reacted with sodium monochloroacetate to yieldsodium carboxymethyl cellulose.

3

An idealized unit structure of CMC is depicted in figure 4. The CMC shown here has a D.S.(Degree of Substitution ) of 1.0. If the remaining two hydroxyl groups on this unit becamesubstituted, the D.S. would be 3.0. A D.S. of 3.0 is the theoretical maximum one could attain.

Figure 5 is a pictorial representation of CMC molecules. Note that the carboxymethyl groupsprotrude from the cellulose backbone, such that the hydroxyl groups of the backbone cannot getclose enough to hydrogen bond to each other. The result is that even in the dried state, water canslip in between the CMC molecules and hydrate them, causing them to "peel apart" from eachother and go into solution.

Figure 6 depicts the nomenclature for Hercules cellulose gum. The specific product described iscellulose gum type 7H3SXF. The "7" stands for the degree of substitution. In the food industry,

4

there are "7" and "9" types of substitution. The pharmaceutical industry also has a "1.2" type towork with. The "H" signifies a high viscosity grade, and the "3" is a reference point which definesthe maximum viscosity of the gum in a 1% solution at 25C (in this case, 3000 centipoise). Thereare "L", "M", and "H" types, representing low, medium, and high viscosity respectively. The "S"stands for special rheological properties (smooth flow). There are "S" types for smooth flow, and"O" types for tolerance in acidic systems. Both of these types show considerably less thixotropythan the randomly substituted regular types of cellulose gum (more will be said about this later).The "X" stands for fine grind material, while a "C" would indicate a coarse particle size, and noletter would indicate a "regular" particle size. The "F" represents food grade (FCC), while a "P"would be pharmaceutical grade (USP).

Some typical viscosity values are shown in Figure 7. Please note that "L" and "M" types aremeasured at a 2% concentration, while "H" types are measured at 1%. Figure 8 shows theconcentration versus viscosity relationship in a more visual fashion.

The effect of the Degree of Substitution on the properties of CMC is shown in figure 9. Toleranceto salt increases and tendency towards thixotropic behavior decreases as the degree ofsubstitution increases.

5

There is another factor which is as important as the Degree of Substitution, and that is the"Uniformity of Substitution", which is shown visually in Figure 10. The "smooth" or non-substitutedregions of a non-uniformly substituted molecule behave just like cellulose because they are stillcellulose! These regions can hydrogen bond to a similar region on an adjacent molecule, leadingto the buildup of a loose gel network ( Figure 11 ).

This buildup is time dependent, and is called "thixotropy". The loose gel network can be disruptedby shearing the CMC solution, but upon standing under no shear conditions the network willreform over time.

Visually, the difference between uniformly and non-uniformly substituted CMC solutions can beseen in Figure 12. Smooth flowing CMC types are desirable for food systems such as syrups orfrostings where smooth consistency is a must. Thixotropic CMC would find use in structured,grainy foods such as sauces or purees.

6

Cellulose gum is probably the fastest gum to hydrate in cold water. Consequently, it is the gummost like to form lumps when dispersed into water, due to it's rapid swelling in water. Toovercome the problem described above, four procedures are recommended in Figure 13:

Method 1: direct addition:Here the gum is added directly to the vortex of a vigorously agitated body of water. The rate ofaddition should be slow enough to keep the particles separated, but fast enough so that all of thegum is added before the vortex disappears. The reason for this is that it is extremely difficult tothicken an already viscous solution of cellulose gum by adding more dry powder. The directaddition method is usually encountered in highly controlled processing situations.

Method 2: dry blending:In this method, the CMC is dispersed with other dry ingredients, such as sugar, prior to theiraddition to aqueous systems. The other particles serve to keep the CMC particles away from eachother. Commonly, one part of CMC is mixed with five to ten parts sugar to effectively preventlumping. The dry mix beverage is a classic example of this dispersion technique.

Method 3: dispersion in a water miscible non-solvent:Cellulose gum may be dispersed in glycerine, ethanol, or propylene glycol and the slurry is thenadded to water. An off-shoot of this method is to disperse the gum in corn syrup, and then add themixture to water with the aid of agitation.

7

Method 4: mixing device:Another method for the addition of cellulose gum to food systems in plant operations is the use ofa stainless steel mixing device (figure 14). The gum is fed through a smooth wall funnel into awater jet eductor, where it is dispersed by the turbulence of water flowing at high velocity. Eachparticle is individually wetted out to give a uniform solution. Under optimum conditions, cellulosegum leaving the eductor is about 80 - 90% hydrated.

ADD THE GUM FIRST! (Figure 15) This is a general rule to follow when adding cellulose gum towater in all food formulations.

8

As an example of the importance of order of addition, Figure 16 is a graph of CMC viscosityversus salt concentration. In one case, the CMC was dissolved in the water before the salt, andthe salt had a minimal effect on the viscosity of the solution. In the other case, the CMC wasdissolved AFTER the salt, and the resulting final viscosity was much lower, especially as the saltconcentration increases.

Figure 17 gives an idea of how cellulose gum is effected by increasingly stronger salt solutions,and by the uniformity of substitution. Going from distilled water to 4% sodium chloride drops theviscosity by a factor of about 12 for 7HF, and by about 3 for the more evenly substituted 7H3SF.The proportions are similar when going to a saturated salt solution ( last column ).

9

Figure 18 shows the effect of some other ions on the viscosity of a CMC solution. The Aluminumsalt actually increases the viscosity of CMC because it has the steric capability of gelling CMC.Unfortunately, for taste reasons, this has little application in the food industry.

Figure 19 shows the effect of water / non-solvent mixtures on the viscosity of CMC. In this case,the non-solvent is glycerin. The maximum viscosity is reached with a 30/70 mixture of water andglycerin. At higher than 70% concentrations of glycerin, the CMC is not fully in solution and thusdoes not give as much viscosity. At lower than 50% glycerin, there is less "crowding" and moreavailiable water for hydration, thus the CMC viscosity is lower.

10

Figure 20 shows that the viscosity of CMC, like most other water soluble polymers, decreases withincreasing temperature. Under normal conditions, this effect is reversible (ie: raising or loweringthe solution temperature has no permanent effect on the viscosity characteristics of the solution).However prolonged heating at extremely high temperatures will permanently degrade the cellulosegum (depolymerization) which results in a viscosity decrease. What this means to the foodtechnologist is that CMC is not particularly retort stable.

Figure 21 indicates that CMC, like most food gums, is pseudoplastic. This means that theapparent viscosity will decrease at increasing shear rates, but the effect is totally reversible. Assoon as the shear is stopped, the viscosity returns to it's original value.

11

CMC is more tolerant to the presence of ethanol than most other food gums (Figure 22). Thismakes cellulose gum useful for cordials and other low alcohol content beverages which requireoptical transparency.

CMC will give a synergistic viscosity increase with other hydrocolloids such as guar or locust beangum ( Figure 23 ). If one were to mix a 1% guar solution of 3800 centipoise with a 1% CMCsolution of 4000 centipoise, the net result is not the 3900 centipoise average of the two; it will becloser to 6500 centipoise. There are more average "collisions per second" between unlikemolecules, which results in this synergistic viscosity increase.

12

Food applications ( Figure 25):

The availability of cellulose gum in different viscosity grades, particle sizes, special rheologicalgrades, and combinations thereof permits tailor-made application of CMC to many different foodsystems. The following is a brief discussion of some of these applications:

Cake mixes

CMC is used to improve the moisture retention in cake mixes, as a dried out cake is quiteobjectionable organoleptically. High D.S. types are preferred in cake mixes for maximum moisturebinding. CMC also controls batter viscosity, imparts tolerance during mixing, protects againstleavening loss, improves cake volume, and controls the uniformity of the cross sectional grain ofthe cake. For ease of mixing, fine grind types of CMC are preferred in cake mixes for rapid entryinto solution. The homemaker does not want to spend all day mixing a cake.

Frostings and Icings

CMC may be used in frostings and icings to toughen the film prevent sticking to the package andreduce sugar crystal growth (graininess). In ready-to-spread frostings CMC helps stabilize theemulsion and adds creaminess. Most important, CMC prevents the icing or frosting from dryingout. Uniformity substituted CMC (S types) are recommended to give a smooth icing or frosting.

Pie fillings

In starch based pie fillings, the addition of a small amount of CMC will prevent cracking controlsyneresis and firm the texture. The use of uniformity substituted 0 types of CMC are preferred forstability in acidic fillings such as in a lemon pie filling.

13

Dairy products

CMC was originally pioneered in ice cream and today this application still remains as one of thelargest single uses for the gum. In ice cream CMC prevents ice crystal growth, inhibits lactosecrystal growth (sandiness); imparts mix viscosity and body to the finished product, gives correctmeltdown, and provides freeze/thaw stability (heat shock control). The use of coarse particle sizetypes of CMC are preferred for ice cream applications (dispersion) because of poor mixingconditions commonly encountered in dairies. CMC is utilized as a stabilizer in many other dairyproducts such as egg nog, soft serve ice cream, milk shakes, and ice cream ripples.

Pancake syrup

CMC enjoys widespread use in regular, reduced calorie and dietetic pancake syrups. Here theexcellent clarity, viscosity ability compatibility with sugar and non caloric characteristics of the gumare put to good use.

Dry mix beverages

The ability of CMC to hydrate rapidly and viscosity in aqueous systems for body and mouthfeel isused in instant breakfast drinks instant fruit drinks hot cocoa mixes and low calorie dry mixbeverages. Uniformity substituted low or medium viscosity fine grind types of CMC are mostfrequently used in these products in order to minimize "fish eye" formation. High viscosity types ofCMC are not recommended in these products regardless of particle size since higher molecularweight types take longer to dissolve and are more prone to form fisheyes if dispersion and energyinput (stirring) are not optimum.

Pet foods and animal feed

In semi-moist pet foods, CMC facilitates extrusion, binds moisture, and improves the cosmeticappearance of the product. In dry gravy-forming pet foods CMC is "dusted" onto tallow coated"kibble" with other ingredients, so that upon reconstitution a rich viscous shiny gravy evolves.Another animal food application for CMC is its use as a physical binder in pelleted animal feeds. Asmall amount of low viscosity CMC in the product holds the pellet together and preventsaccumulation of fines in the product package during shipment. Additionally, the gum assists theextrusion process during manufacture of the pellets and helps reduce energy consumption by thepellet mill.

14

CMC greatly modifies the behavior of water in sugar solutions (figure 26). Combinations of sugarand CMC display a significant "boost" in viscosity which is believed to be the consequence of acrowding mechanism. Cellulose gum decreases the tendency towards syneresis in high sugarfood systems by serving as a water binder. Most importantly, CMC also reduces the rate of sugarcrystal growth and crystal size in concentrated sugar systems. This functionality becomesimportant in confectionery applications such as fondants ( Figure 27 below).

Just as CMC controls sugar crystal growth in confectionery applications, it controls ice crystalgrowth in ice cream the same way ( Figure 28 ). Texturally, it is desirable to have a large numberof small ice crystals (smooth) rather than a small number of large ones (sandy).

15

A few cautions about using cellulose gum in food products: Exposure to UV light and entrained airin a food system should be minimized to prevent degradation of the gum. Molecular oxygen willcause the gum to breakdown by a free radical mechanism similar to that which occurs during theautoxidation of lipids. The presence of cations (calcium, iron, aluminum) will accelerate theprocess. Therefore it is recommended that a sequestrant such as sodium hexametaphosphate beused in systems where CMC is exposed to air and cations.

To summarize, cellulose gum is a very useful hydrocolloid for the food industry. It's water bindingability is second to none, and it is completely transparent in solution. CMC can add viscosity ormouthfeel, control syneresis, and control the rate / size of crystal growth.