A Good Overview Of Scientific, Technical And Commercial Aspects For Gellan Gum

Gellan gum is a fermentation polysaccharide produced by the microorganism Sphingomonas elodea. It has a straight chain structure based on repeating glucose, rhamnose and glucuronic acid units with side groups of acyl groups. 

Gellan gum hydrates in hot water and the low acyl form also hydrates in cold water with sequestrants. On cooling, native high-acyl gellan gum gives gels that are soft and elastic. Low-acyl gellan gum gels at very low concentrations using both monovalent and divalent cations to give firm, brittle textures with excellent thermal stability. 

Combinations of gellan gum can be used to control syneresis and form a range of textures from soft and elastic to firm and brittle. A major food application is water dessert gels, particularly for Asian desserts. Other significant applications include confectionery, dairy desserts and bakery fillings. At levels too low to form a demoldable gel, gellan gum can form fluid gels that can suspend particulates in sauces and dressings and fruit pulp in beverages.

Manufacture 

All the different forms of gellan gum are produced from the same basic fermentation process (see below,for more please visit:www.cinogel.com which is a professional manufacturer & supplier of gellan gum in China). Large sterile fermentation vessels are used to allow the bacteria to convert simple sugars and other nutrients into the gellan gum polysaccharide. Once the cells have been killed, several different process steps can be followed to produce to four different product types. At present, the low-acyl, unclarified version is not produced commercially. 

Even within a defined product type, such as clarified, low-acyl gellan gum, many different commercial grades can exist depending upon the intended use of the product.

Properties such as particle size and gel strength can vary between different grades. Additionally, gellan gum is often blended with other ingredients to make products with properties that are targeted to the needs of specific applications. 

 Chemical Composition

The molecular structure of gellan gum is a straight chain based on repeating glucose, rhamnose and glucuronic acid units (see below). In its native or high-acyl form, two acyl substituents – acetate and glycerate – are present. Both substituents are located on the same glucose residue and, on average, there is one glycerate per repeat and one acetate per every two repeating unit (Kuo et al., 1986). In low-acyl gellan gum, the acyl groups are absent.  

The structure of gellan gum has been studied extensively using techniques such as X-ray diffraction and molecular modeling (Chandrasekaran et al., 1988a,b, 1992; Chandrasekaran and Thailambal, 1990). The studies suggest that gellan gum polymer adopts a double helical structure after heating and cooling. If the cooling is done in the presence of cations, the double helices aggregate into long-range networks. When the gum concentration is high enough, this network structure becomes a demoldable gel. The acyl groups on the high-acyl gellan gum help stabilize the double helix, but they interfere with the double helix aggregation.

The resulting high-acyl gellan gum gel is soft and elastic. The low-acyl form of gellan gum, without the interfering acyl groups, forms gels that are very firm and brittle. 

Functional Properties

The presence or absence of the acyl groups on the gellan gum polysaccharide backbone has a profound effect on its functional properties. Therefore, when discussing hydration or gel properties, it is important to distinguish between low- and high-acyl gellan gum types. 

Hydration of low-acyl gellan gum

The hydration temperature of low-acyl gellan gum is sensitive to the ionic environment and particularly sensitive to divalent cations (see below). Low-acyl gellan gum itself contains 

divalent cations and will only partially hydrate in cold, deionized water. 

Hydration is further inhibited by the divalent ions present in most water supplies. 

This effect makes low-acyl gellan gum easy to disperse in cold water without forming lumps. Subsequently, the gum can be hydrated by adding sequestrants or chelators, such as citrates and phosphates, to control the divalent ions, heat or a combination of both. Hence, the hydration temperature of low-acyl gellan gum can be effectively controlled (see below picture). 

Without sequestrants, low-acyl gellan gum requires a temperature above about 75◦C (167◦F) to fully hydrate in soft water. However, it can be hydrated in cold, soft water using 0.12% sodium citrate, as given in Table below.

Hydration guide for low-acyl products

The solution pH also affects the hydration characteristics of low-acyl gellan gum (see
below). At pH values above the pKa of gellan gum, about pH 3.6, the gum is in a form
that allows easy dissolution. If the solution pH is below 3.6, however, the gum will exist in a predominately acid form which is not completely soluble. 

Therefore, when formulating acidic products, the acid should be added after the gum has been hydrated. 

Dissolved sugars have an effect on gellan gum hydration (see below). Up to dissolved
sugar levels of 25% or so, hydration proceeds in a normal manner. As the sugar level increases above this point, more heat needs to be applied to fully solubilize the gellan gum. When using gellan gum, it is always better to keep the level of dissolved sugars low until after the gum has been hydrated. After gum hydration, the remaining sugar solids can be added. 

Hydration of high-acyl gellan gum  

High-acyl gellan gum swells in deionized water, creating a consistency like a swollen
starch paste. Low levels of sodium ions inhibit this swelling behavior so the addition of
sodium salts is a useful strategy for improving gum dispersion and for minimizing viscosity during processing. Heat is required to fully hydrate high-acyl gellan gum. While ions affect dispersion and particle-swelling behavior, the full hydration of high-acyl gellan gum is relatively insensitive to ions. High-acyl gellan gum hydrates between 70◦C and 80◦C (158◦F and 176◦F), even in relatively high ion concentrations (see below). In contrast  to low-acyl gellan gum, the calcium effect on high-acyl gellan gum is small. Because calcium has little influence on the hydration temperature, sequestrants do not facilitate hydration.

Both low- and high-acyl forms of gellan gum can be dispersed directly in milk and will hydrate during normal heat processing. As mentioned already, dissolved solids and low pH inhibit gum hydration for both forms of gellan gum. In acidic environments, the pH must be above 4 for good hydration. In high-solids systems, extra care must be taken to ensure that the gellan gum hydrates. 

A fine mesh product is needed to facilitate hydration in the presence of sugars. Gellan gum’s sensitivity to monovalent ions increases in high-solids systems, so  high sequestrant levels will inhibit, rather than aid, gum hydration. The inhibition effect can be avoided by keeping sodium citrate levels less than 0.2%.

An overall strategy for gellan gum hydration is given in below. While designed for the low-acyl form of the gum, these conditions will also permit full hydration of the high-acyl form. As a rule, the gellan gum is added to solutions with low levels of calcium, moderate pH and dissolved sugar levels of less than 25%. Once hydrated, salts, acid and additional sugars can be added to form the final food. 

Gel properties of low-acyl gellan gum

Gellan gels can be formed over a broad range of conditions. The matrix shown in below first describes the gel properties that can be expected in each of the four quadrants. the following 3 pictuers  show how pH and dissolved sugar solids interact.

Quadrant 1 represents a neutral pH value with a low level of dissolved sugar. Much of
the literature published on gellan gum has focused on gels in this domain. Because the pH is not acidic, the carboxyl groups on the gellan gum molecule interact with sodium, potassium, calcium or magnesium counter-ions. This interaction results in a high degree of molecular association and the formation of a long-range network or gel. Gellan gum is an effective gel former in this quadrant, creating demoldable gels at gum concentrations as low as 0.05%.

With only a small amount of dissolved sugar, gellan gum is in a low-viscosity, aqueous
environment. With high molecular mobility, a gel forms quickly upon cooling. The exact temperature of gelation depends upon the cations present and, to a certain extent, upon the cooling rate. The average temperature for gelation is 30–45◦C (86–113◦F) (see above 2nd). 

Complete gelation occurs almost instantly at the gelling temperature, so there is little change in gel properties with storage time. Calcium tolerance is good because gel properties are stable over a range of calcium concentration from 5 to 15 mM, as shown in the neutral pH curve in (above 3rd). Unless low levels of gelling ions are used, these gels do not remelt. 

Quadrant 2 in(above 1st)covers gels formed at neutral pH and higher sugar levels. Gels prepared under high-solids conditions include confections, icings and the like. 

below shows how the strength of these gels varies with calcium level. Compared to the low solids gels in Quadrant 1, these gels are softer and much less calcium sensitive. Because gellan gum is less effective at forming demoldable gels in Quadrant 2, higher gum levels, typically 0.3% or higher, are required.

At higher dissolved solids, the gellan gum molecules are dispersed in a high-viscosity environment. In general, sugars have a plasticizing effect on the gel. Associations between molecular chains of gellan gum are slower to form and they are not as extensive once they do form. Like Quadrant 1 gels, the Quadrant 2 gels form with cooling. Unlike the Quadrant 1 gels, however, gel formation is not always fast in high-solids systems. Even at low temperatures, it can take weeks for gellan gum to develop its full structure. Once formed, high-solids gels are softer and more elastic and they have a greater ability to re-heal after being sheared. Different sources of sugar solids, such as sucrose, glucose and fructose, affect both viscosity and molecular mobility of the gellan gum molecules, so the exact nature of the dissolved solids has a strong influence on the properties of the gellan gum gel. Sucrose has a more pronounced influence on the set time and gel texture than does fructose or glucose. Sucrose lengthens the set time and softens the gel and it also increases the gel’s ability to re-heal after shearing.

Quadrant 3 represents gels with fairly low dissolved sugar levels and acidic pH values.When the pH goes below 3.7 or so, most of the carboxyl groups on the gellan gum molecule are protonated, so they cannot interact with cations. The curves for pH 3 and 4 in Fig. 8.11 show how calcium ions have far less effect on these gels, especially as the pH is lowered. Acid-induced gellan gels do not need calcium to set. Demoldable gels can be made at gum concentrations of 0.05% or less in this quadrant.

Compared to Quadrant 1 gels formed with ions at low solids, low-solids, acidic, gellan
gels are firmer but they are quite brittle. The high brittleness of these gels is often perceived as soft and mushy because the gels break under low levels of strain. The gels have slightly more tendency to synerise than do gels at a more neutral pH. Like Quadrant 1 gels, gel formation in Quadrant 3 occurs quickly with cooling. However, acid-induced gelation generally occurs at a lower temperature than ion-induced gelation, and the resulting gels are not as thermostable. In this quadrant, the gels will not re-heal after shearing.

Quadrant 4 is for acidic gels formed with high levels of dissolved sugar solids. Figure
above shows that the texture of these gels is relatively insensitive to calcium. As the pH drops below the pKa of the gellan gum, these gels get more and more firm because the gelation mechanism changes from ion induced to acid induced. With the plasticizing effect of sugars, however, the gel textures do not become overly brittle like the Quadrant 3 gels. 

Because gellan gum is less effective at forming demoldable gels in Quadrant 4, higher gum use levels, typically 0.3% or higher, are required.

The gelation temperature in Quadrant 4 depends on the level of the sugar solids, as well as the pH and the ion levels. High levels of solids and ions increase the set temperature, while higher pH lowers the set temperature. Like Quadrant 2 gels, the composition of the sugar solids affects both the setting temperature and time. The setting temperature and time are reduced when sugar solids come from fructose, dextrose or sugar alcohols. Sucrose, however, increases the gel temperature and extends the gel set time. In most cases, these acid-induced, high-solids gels do not remelt. As the gels get firmer with lower pH, they also lose the ability to re-heal after shearing. 

Gel properties of high-acyl gellan gum

Overall, the high-acyl form of gellan gum is not as sensitive to cation levels as the low-acyl gellan products. Figure below shows that large changes in the calcium level contribute only small changes in gel properties. Slightly firmer gels result as the calcium level is increased.
Similar effects are seen for magnesium and, to a lesser extent, for sodium and potassium ions.

Adding more dissolved sugar solids to the high-acyl form of gellan gum tends to strengthen the gel slightly (see Fig. below). Again, the effect is less for this form of gellan gum than for the low-acyl form. At solids levels greater than 50%, however, the sugars raise the set temperature, interfere with gelation and plasticize the gel. Higher levels of high-acyl gellan gum are needed to form a demoldable gel in high-solids environments. 

Very low pH values below 3.5 make the high-acyl gellan gum gels soften somewhat as shown in Fig. below. Unlike low-acyl gellan gum, there is no evidence of an acid-induced gel mechanism for high-acyl gellan gum. The gum simply loses the ability to form a gel network as the pH drops. However, over most of the pH range for foods, high-acyl gellan gum gels are not influenced by pH.

Gels made with the high-acyl form of gellan gum generally show little thermal hysteresis
as shown in Fig. below. The setting and melting temperatures increase as the calcium ion
concentration increases. With low ionic strength gels, these two temperatures are within 3◦C  of each other. With high ion levels, the difference increases to 8◦C. The low ionic strength dependence and the low thermal hysteresis reveal that the high-acyl form of gellan gum forms gels as a result of interchain association, lacking the significant cooperative ion cross-linking of the low-acyl form of the gum.

Nongelling network properties  

Both low- and high-acyl gellan gums can be used at concentrations that are too low to form a demoldable gel. While the gellan gum molecules still associate and form a long-range network, the system remains very fluid. These systems are often called ‘fluid gels’.

Fluid gels exhibit a highly pseudoplastic flow property – the viscosity decreases with increasing shear. Therefore, fluid gels are perceived as thin in terms of mouthfeel, because the act of swallowing during consumption creates shear. While low in viscosity, however, fluid gels exhibit a high elastic modulus, which imparts suspension properties to the system. In fact, fluid gels made with gellan gum have a yield stress. A particle trapped in a fluid gel system will not move unless its weight or buoyancy can overcome the yield stress of the network (Fig. below).  

Gum combinations

Earlier in this chapter, it was mentioned that the two forms of gellan gum could be blended to form intermediate texture values. This feature is one of the primary strengths of gellan gum. 

Gellan gum blends appear to be composed of interpenetrating rather than cooperative networks of polymers (Manson and Sperling, 1976; Mao et al., 2000). This structure means that, in most cases, the high-acyl form will set at a higher temperature as shown in previous figures. 

With further cooling, the low-acyl form sets up within the high-acyl network. This ‘gel within a gel’ allows for one form to smoothly transition into the other form as the ratio of low- to high-acyl gellan gum changes. This smooth transition results in the wide range of textures illustrated in Fig. below. 

The flexibility of this blending allows formulators to produce exactly the texture that is needed for an application, while keeping most of the remaining formulation constant.

Blends with other gums are possible and useful. In general, nongelling hydrocolloids do not appreciably change the functionality or texture of gellan gum. High levels of viscosifying gums, such as xanthan gum or cellulose gum, however, can interfere with gellan gum mobility and cross-linking, resulting in softer gels. The antagonistic effect can be used advantageously to maintain a smooth texture when making fluid gels with low-acyl gellan gum.

Blending gellan gum with other gelling hydrocolloids typically results in gels with intermediate properties. For example, low-acyl gellan gum can be used to increase the firmness of soft, elastic gels such as iota carrageenan, gelatin or combinations of xanthan gum and locust bean gum. Adding gellan gum to other gelling agents can be particularly advantageous for altering the setting and melting properties of the other gum systems. For example, gellan gum can be used to raise the set temperature of gelatin-based confections and dessert gels.

Synergies with gelatin, carrageenan and xyloglucans have been reported in the literature (Blecker et al., 2000; Loh et al., 2002; Ikeda et al., 2004). However, these synergies are likely based on ionic effects and volume exclusion rather than on direct gum interactions.

In other cases, it may be desirable to mix gellan gums with other gums to take advantage of their functional properties. For example, gellan gum can be mixed with gelatin to improve the heat stability of gelatin gels. Additionally, confectionery products, such as gummy candies, can be made without gelatin by using mixtures of carrageenan with gellan gum. 

Regulatory Status

Gellan gum first received approval for food use in Japan in 1988. It is now approved for food, nonfood, cosmetic and pharmaceutical use in the USA, Canada, Australia and many other countries in Latin America, South America, Asia and the European Union.

Gellan gum first appeared in the USP/NF first Supplement 1 April 2004 USP 27/NF 22. The NF monograph appears in the current USP/NF. Gellan gum is an approved FDA food additive under 21 CFR 172.665. Gellan gum appears as E418 in the European Community Directive EC/95/2 in Annex 1. Gellan gum is listed in the Food Chemicals Codex, Canada Food and Drug Act (Division 16, Table IV, G.2) and the Japanese Specifications and Standards for Food Additives (JSSFA).

Both the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the European Community Scientific Committee for Food have given gellan gum an acceptable daily intake (ADI) of ‘not specified’. On food labels, high-acyl and low-acyl gellan gum or any combination of the two may be declared under the name of ‘Stabiliser: E418’ or ‘Stabiliser: Gellan Gum’ in the EU. 

Applications

With its unique and versatile properties, gellan gum is used commercially in a wide range of food applications. These applications can be generally categorized into six application areas:

Water-based gels ,Bakery applications,Dairy foods,Beverages,Confections,Fruit applications

Within these broad categories, a number of specific applications of gellan gum are discussed in greater detail.  

Water-based gels  

The most common commercial use of gellan gum is creating water-based gels.  

Dessert gels

In dessert gels, low-acyl gellan gum creates a firm, brittle texture with excellent clarity and heat stability. Because it is highly efficient at forming gels, the gellan gum use level is very low, with typical use levels for dessert gels ranging from 0.15 to 0.35%. Gellan gum also provides particularly good flavor release compared to other gums (Morris, 1994; Costellet al., 2001). However, the brittle texture of low-acyl gels is not typical of common dessert gels. Therefore, low-acyl gellan gum is often blended with other gelling agents to provide softer, more elastic textures. A blend of low-acyl gellan gum with xanthan gum and locust bean gum, targeted for a dessert gel texture, is commercially available.  

The recent commercialization of clarified, high-acyl gellan gum also makes it possible to create a range of textures using blends of low- and high-acyl gellan gum. The ingredient declaration of the resulting product is simplified because both types of gum are still labeled as gellan gum. A ratio of 80% high-acyl gellan gum to 20% low-acyl gellan gum results in a gel texture that is similar to the texture of a gelatin dessert gel.

Sensitivity to heat and acid limits both the batch size and the pasteurization conditions for most gums that are used in dessert gels. Gellan gum’s exceptional stability to heat and acid, however, allows larger batch sizes and more flexibility with pasteurization conditions.

For example, unpasteurized fruit can be added to the cup before filling with the gel and the pasteurization conditions can be extended, so that the fruit is fully pasteurized in the sealed cup. Gellan gum’s acid stability also allows dessert gels to be formulated at lower pH to enhance the flavor impact of the gels.

Multi-layer RTE (ready-to-eat) dessert gels are popular in Asia. The different layers can contain different colors, textures and flavors. Because gellan gum has a high melting temperature, hot gum solutions can be poured on top of a gelled gellan gum layer without melting it. Gellan gum can also be used to make heat-stable colored beads or shaped novelties that can be used as inclusions in a clear gel matrix.  

Drinking jellies 

Drinking jellies are formulated in a similar way to dessert gels, but lower levels of gelling agents are used to create a very soft gel. There are different types and textures of drinking jellies, depending on how they will be consumed. Some drinking jellies are soft enough to be sucked through a straw. Others will be crushed and squeezed out of a pouch.

In many Asian countries, drinking jellies are consumed simply for their interesting textures. Increasingly, however, gellan gum drinking gels are being formulated to provide enhanced nutrition or nutraceutical benefits. Sports gels are an example of such a product.

They are typically packaged in pouches with tear-off tops for consumption while exercising. The gelled contents provide water and nutrients without spilling and the juicy gel bits slide down the throat without leaving a sticky coating.

Low-acyl gellan gum is typically preferred in these applications because the brittle gels are easy to crush and break. Once broken, the gels quickly exude water, enhancing flavor release and increasing the lubricity of the gel. 

Typical gellan gum use levels range from 0.05% to 0.1%. However, drinking jellies with different textures can be formulated by adding other gums, including high-acyl gellan gum. 

Asian foods

In many Asian countries, water-based gels are a traditional food. In Japan, for example, mitsumame is a popular dessert, made of firmly gelled cubes. Tokoroten, a clear jelly noodle, is another example of a popular Asian water-based jelly. Traditionally, these dishes were made with agar-agar, but the firm, brittle texture of low-acyl gellan gum is well suited for these gels.

In Asia, gellan gum is often used to simulate the texture of some traditional foods such as bird’s nest soup. Authentic bird’s nest soup is made with the dried saliva from the nests of swiftlet birds, but it is expensive due to its limited supply. Gellan gum is often used to create an inexpensive imitation bird’s nest. Low-acyl gellan provides a fine, brittle texture and provides heat stability for pasteurizing or retorting these products. 

Bakery applications  

Gellan gum is used in the commercial bakery applications almost as frequently as it is used in water gels. Many different applications are found in the bakery segment. 

Bakery mixes

Gellan gum is highly functional in bakery dry mixes. Unlike some other gums commonly found in such products, low-acyl gellan gum does not readily hydrate in cold water. 

Using low-acyl gellan gum in a bakery formulation does not increase the batter viscosity because the gum does not hydrate immediately. However, gellan gum hydrates in the oven during baking, so it provides moisture retention and shelf life extension in the final baked goods. 

Gellan gum finds most of its use in dry mixes formulated to produce thick batters, like brownies, where excessive viscosity would impede batter spread in a baking pan. The textural effects of gellan gum are obtained at low use levels, typically ranging from 0.08% to 1.0% gum.  

Bakery fillings

When considering gellan gum in bakery filling applications, it is convenient to discuss bakery fillings in terms of low-solids, medium-solids and high-solids fillings. Low-solids fillings have up to 45% soluble solids, medium solids fillings have 45–65% soluble solids and high-solids fillings have in excess of 65% soluble solids.  

Low-solids fillings

Because of its very high melting temperature, low-acyl gellan gum is used to improve the bake stability of low-solids fillings. High melting temperatures are obtained when the gels are set by calcium cross-linking. Used alone, low-acyl gellan gum creates a firm brittle texture that is difficult to pump or spread. However, when used with modified starch, a smooth pumpable texture with good flavor release and heat stability can be obtained.
Typical use levels for gellan gum range from 0.08% to 0.3%.

Texture and the pumpability of the filling can be adjusted by changing the levels and ratio of gellan gum and starch. Divalent salts, like calcium, may be added to increase the firmness and heat stability of the filling.

A combination of low-acyl and high-acyl gellan gum is appropriate when the filling is applied post-baking.  

Medium-solids fillings

In medium-solids fillings, gellan gum can be used without starch when sucrose is the major source of solids. Calcium cross-linked gels can be sheared and pumped with a smooth texture that will re-heal with time. However, the softening effects of sucrose on the gel network generally call for higher levels of gum to maintain heat stability. Use levels typically range from 0.25% to 0.40% gum.

Special care must be taken when the pH of the filling is below 3.5. The combination of calcium cross-linking and acid gelation with higher solids can result in very high setting temperatures. Formulating gellan gum fillings with high levels of calcium at low pH can result in pregelation. Because of this, most medium solids fillings with gellan gum are formulated with high fructose corn syrup because fructose tends to lower the setting temperature. With higher levels of fructose, the gels are firmer, but starch is usually needed to provide a smooth texture.

High solids fillings

In high solids, water mobility is severely limited. Gellan gum gel does not form a gel network using ionic cross-links in this environment. Control of gellan gum properties in this environment is only available through the manipulation of pH. As the pH approaches 3.0, a very firm, heat-stable gel can be formed. Using starches to modify the gel to give a smooth texture, this system can provide an excellent, high-solids bakery filling.
Because sugars interfere with the gel network, higher levels of gellan gum are needed to provide good heat stability compared to lower solids fillings and typical use levels range from 0.3% to0.7% gum.  

Binding systems

Gellan gum is an effective binder and film former. Binding is particularly important for producers of nutritional bars and high protein bars. These products typically contain protein nuggets that are bound together with a mixture of corn syrup and stabilizer. If the binding system contains too much moisture, the bar will become soggy. The binding system should also be short textured and nonsticky. Low-acyl gellan gum is commonly used in nutritional bars because it can be hydrated directly in corn syrup or glycerin.  

Glazes, icings and frostings

The bulk composition of glazes, icings and frostings is undissolved powdered sugar.
Stabilizers are effective only in the saturated sugar syrup that glues the particles of sugar together.

Because the soluble solids in the syrup are mostly sugar, working with gellan gum in this system can be challenging.

To be effective, gellan gum must form a network or a gel, but the high level of sucrose interferes with calcium cross-linking. The secret to using gellan gum successfully in these systems is to create a sodium-crosslinked gel. Without any sodium ions, no network will be formed. However, too much sodium weakens the network. Sodium control is typically achieved through the use of sodium citrate, which is commonly used as a sequestrant and hydration aid. The optimum level of sodium citrate depends on the amount of water in the formulation, but the saturated syrup should not contain more than 0.1% sodium citrate. 
The gel network sets at approximately 37◦C. The sucrose gel is thixotropic, so shearing through the set point is not a problem. However, there is an increase in the icing viscosity at the set temperature, so, for glazes and flat icings, it is advantageous to apply the icing before this viscosity develops. For frostings, it is best to shear though the set point.  

Cultured dairy foods

Cultured dairy foods are based on the fermentation of milk. Typical products include yogurts, sour creams and cheeses. Gelatin is commonly used to stabilize many of these products, but it is not acceptable for consumers following vegan, Kosher or Halal diets.  

Yogurts can be produced using two methods: (1) cup set and (2) stirred. Cup set yogurt is cultured directly in a serving-sized cup, which may have fruit on the bottom. Stirred yogurt is cultured in a large vat and, after fermentation, the curd is stirred with a fruit preparation and deposited into a cup. Both low- and high-acyl gellan gums can be used in a stirred yogurt, but cup-set yogurts are made only with high-acyl gellan gum. Low-acyl gellan gum creates a lumpy texture after culturing that requires mixing to create a smooth texture.

Gellan gum is typically added to the raw milk prior to homogenization and pasteurization.
These processes, which are typical in yogurt production, will hydrate the gum. The use of low-acyl gellan gum must be limited to less than 0.06% or a grainy texture will result. High-acyl gellan gum can be used at up to 0.1% gum before excessive graininess develops.At these use levels, gellan gum adds a light texture and significantly reduces whey-off. Pectin or starch can be added to build a heavier body if desired.

Sour cream production is analogous to yogurt, but the fermentation includes butterfat. Like yogurt, sour cream is commonly stabilized with gelatin. Both low- and high-acyl gellan gums are used to stabilize this product. Low-acyl gellan gum is used to add heat stability to the sour cream, so that it retains structure after being added to hot foods. High-acyl gellan gum is used to provide a thixotropic rheology to the sour cream, allowing the structure to reform after stirring.  

Beverages

Shelf-stable, ready-to-drink (RTD) juice beverages are steadily growing in popularity. However, one drawback is that many juices suffer from both juice cloud settling and pulp separation during storage.

Gellan gum can be used to overcome cloud and pulp settling in juices while providing a mouthfeel that is light and refreshing when compared to other stabilizers. 
Gellan gum can stabilize beverages with a pH as low as 3.0. Gellan gum has low protein reactivity which makes it compatible with a wide variety of juices. Gellan gum is easy to disperse and hydrate and so it can be used in most juice processing plants without having to add special mixing equipment.

Combinations of gellan gum and pectin are particularly advantageous in this application. A special blend high-acyl gellan gum and pectin is commercially available for this application. The gum blend is added to the juice prior to sterilization. Hydration is achieved simply by heating the juice to 85◦C (185◦F) for 30 s. These processing conditions are commonly used to sterilize juices in hot-fill bottling operations. For optimum stability of juice clouds, pulp and calcium salts with minimal increase in mouthfeel, the high-acyl gellan gum and pectin blend should be used at levels from 0.25% to 0.30%.

Neutral pH dairy beverages, including chocolate and other flavored milks, ready-to-drink coffee or tea and nutritional beverages, can be stabilized with gellan gum. Carrageenan is often used in these systems because of its synergistic interaction with milk caseins. Gellan gum does not have the same synergy with milk, but its independence of milk proteins allows it to be used in products with low milk protein and in systems with low-quality or heat-damaged proteins as will be found in spray-dried milk powders.

Most grades of high-acyl gellan gum are standardized on gel strength but this is not related to its suspension properties. Standard grades of high-acyl gellan gum may also develop off flavors in neutral pH, long shelf life milk systems. Consequently, CINOGEL gellan gum has been specially developed and standardized as a beverage stabilizer for use in neutral pH, long shelf life milk systems without developing off-flavors with storage time.  

Soy milk stabilization can be more difficult to stabilize than dairy milk because soy sources usually contain large amounts of insoluble material. Carrageenan does not have a strong synergistic interaction with soy protein, so higher levels of carrageenan and higher viscosities are needed to fully stabilize the beverage. High-acyl gellan gum functions independently of soy protein type or concentration. This independence is particularly advantageous because the types of soy protein vary from ground whole beans or concentrates and isolates. A special grade of gellan gum has been specially developed to work as a beverage stabilizer in soy protein systems.  

Confections

Low-acyl gellan gum is used commercially in high-solids, gelled confections. It produces jellies with short texture and good flavor release. Because of the high melting temperature, low-acyl gellan gum is also used to increase the melting temperature of gelatin gummy confections. The gum use level depends on the structure needed. A soft textured jelly can be made with 0.35% gum, but use levels around 0.75% are needed to produce a firm jelly.

To make smooth-textured confections, low-acyl gellan gum must be hydrated in the absence of divalent ions. Unsequestered divalent ions will create a grainy texture during cookup. It is also difficult to add divalent ions to a high-solids gellan gum solution and control the gelation. Therefore, it is typical to hydrate the gum using low levels of sequestrants, such as sodium citrate, and then to use acids to set the gel after cooking. The gel texture is largely controlled by the pH, but calcium released from the sequestrant at low pH will raise the set temperature and shorten the set time. By controlling both pH and calcium, it is possible to obtain a variety of textures and setting profiles.

Gellan gum can be used to improve the functionality of other hydrocolloids in confections.
Confections made from starch can take several days to develop a demoldable texture.Adding a small amount of gellan gum to a starch formulation significantly reduces the set time, so the gels can be demolded on the same day. Gummy confections made with gelatin also benefit from the addition of gellan gum. Gellan gum increases the heat stability so that the individual candy pieces do not melt together when exposed to a warm environment.  

Fruit applications

However, gellan gum is used in a few additional fruit applications, including low-solids jam and yogurt fruit preparations. With increased consumer interest in nutrition and diet, food manufacturers are continually challenged to create high-quality, low-sugar food products. This is particularly true in the development of imitation jams or spreads which cannot rely upon sugar and corn syrups to provide body and texture in the final product. The challenge for manufacturers of these products is to develop the necessary physical properties of set, spread and stability, while maintaining natural fruit flavors and colors. Pectin has long been used in the manufacture of jams and jellies, but its gelling mechanism requires some sugar and a relatively low pH.

Gellan gum is used to work around these key formulation requirements, allowing low calorie jams to be formulated without sugar. Yogurt fruit preparations use gelling agents to provide viscosity and suspension of fruit pieces. High-acyl gellan gum has ideal properties in this application. With low calcium and protein sensitivity, the powder can be added directly to the fruit and it can be heated just like starch. With a high setting temperature, high-acyl gellan gum suspends fruit at a use levels from 0.08% to 1.0% gum, making it one of the most cost-effective stabilizing systems available.

Miscellaneous applications

Gellan gum can also be in sauces, films and adhesion systems.

Gellan gum fluid gels are used to suspend herbs in no-fat salad dressings. It is also used in full fat dressings that are sold with separating oil and aqueous layers. The fluid gel is used to suspend herbs in the aqueous layer.

Fluid gels are also used in some hot sauces to suspend particulates of chili peppers. Gellan gum is able to tolerate the harsh environment while minimizing viscosity without masking flavors.

Gellan gum solutions can be dried to form a film. The film is a poor moisture barrier, but it is an excellent oil barrier. Gellan gum can be used to coat substrates such as french fries or chicken. It will then act as an oil barrier during subsequent frying, resulting in a significant reduction of fat in the final product.  

Future Developments

Currently, gellan gum is available in its high or low-acyl forms. However, it is theoretically possible to produce gellan gum with intermediate levels of acyl content. The acyl content will dramatically affect the gum functionality so it may be possible to target very specific gel textures and properties by making products with a different acyl content.

With improvements in gellan gum manufacturing processes, it may also be possible to produce gellan gum with significantly greater molecular weight. 

Gellan gum with exceptionally high gel strength would result from the higher molecular weight. This material would make gellan gum more cost-effective in many applications and it would also be expected to expand gellan gum’s functionality into new applications .