Gellan Gum and Its Applications – A Review

Jigar N. Shah

Mr. Jigar N. Shah

For decades microbial exopolysaccharides have been invaluable ingredients in the food industry, as well as having many attractive pharmaceutical and chemical applications. The biopolymer gellan is a more recent addition to the family of microbial polysaccharides that is gaining much importance due to its novel property of forming thermo-reversible gels when heated and cooled. It has applications in diverse fields in the food, pharmaceutical and many other industries.1

Gellan gum is an anionic, high molecular weight, deacetylated exocellular polysaccharide gum produced as a fermentation product by a pure culture of Pseudomonas elodea2, with a tetrasaccharide repeating unit of one α-L-rhamnose, one β- D-glucuronic acid and two β-D-glucose residues3,4.  The production organism is an aerobic, gram-negative bacterium, which has been very well characterized and demonstrated to be non-pathogenic5. This organism was found during an extensive screening programme seeking naturally occurring hydrocolloids with useful properties.  

Gellan gum has the characteristic property of temperature-dependent and cation-induced gelation. This gelation involves the formation of double helical junction zones followed by a Gellan gumregation of the double helical segments to form a three-dimensional network by complexation with cations and hydrogen bonding with water.

Chemical structure7 of the polysaccharide has been determined.  It has a tetrasaccharide repeat unit consisting of two glucose (Glc) residues, one glucuronic acid (GlcA) residue, and one rhamnose (Rha) residue8. These are linked together to give a tetrasaccharide repeat unit (Fig. 1). The native polysaccharide is partially esterified with L-glycerate and acetate9 but the commercial product Gelrite® has been completely de-esterified by alkali Treatment10, 11. The exact molecular formula of gellan gum may vary slightly (e.g., depending on the degree to which the glucuronic acid is neutralized with various salts).

The structure of deacetylated Gellan Gum

The structure of deacetylated Gellan Gum

Fig. 1 – The structure of deacetylated Gellan Gum (Gellan gum report)

The glucuronic acid is neutralized by the presence of potassium, calcium, and magnesium ions.  The relative concentrations of these ions will control the physical properties of the gum material such as gel strength, melting point and setting point.  The gum has been proposed for use as a stabilizer and thickener in foods.

Types of Gellan Gum:

There are three basic forms of gellan gum product which have been characterized and are distinguished by their 1) polysaccharide content, 2) the percent of o-acetyl substitution on the polysaccharide and 3) the protein content (including nucleic residues and other organic nitrogen sources). 

It is available in two forms (high or low acyl content). The acyl groups have a profound influence on gel characteristics. The high acyl form produces soft very elastic and non-brittle gels, while the low acyl form produces firm, non-elastic and brittle gels. They may be used alone or blended to give products with the desired characteristics12.

Gellan Gum is available in a clarified form (KELCOGEL7) for foods and industrial products and a clarified form of (GELRITE7) for microbiological media, plant tissue culture, and pharmaceutical applications. Gellan gum includes non-clarified, clarified, and partially-clarified native, deacetylated and partially deacetylated forms as well as mixtures thereof and the like13.

Mechanism of action of Gellan gum:

Gellan gum is a multi-functional gelling agent can be used alone or in combination with other products to produce a wide variety of interesting textures.  Gellan gum acts as a thickening or gelling agent and can produce textures in the final product that vary from hard, non-elastic, brittle gels to fluid gels. The formulation adopted was a gellan solution containing calcium chloride (as a source of Ca2+), and sodium citrate, which complexes the free Ca2+ ions and releases them only in the acidic environment of the stomach. In this way, the formulation remains in liquid form until it reaches the stomach, where gelation of gellan gum is instantaneous.

Action of the different substances:

Gellan gum is produced from S. elodea by a pure-culture fermentation process and then recovered with isopropyl alcohol. The gellan gum obtained from the microbial culture includes acetyl and L-glycerate groups that are removed (i.e., the gellan gum is deacylated) to some extent with the addition of an alkali. The gellan gum is then precipitated from the fermentation medium with isopropyl alcohol14. The gel thickness for specific products can be controlled by manipulating the addition of alkali cations (i.e., by adding potassium, magnesium, calcium, and/or sodium salts)14. Native gellan gum can change from soft, elastic thermo-reversible gels to harder and more-brittle gels with higher thermal stability by deacylation.15-18. The gelling mechanism is cation-induced ability to gel with any cation, including counterion of an active ingredient. By varying ion content and/or gel concentration, the gel texture can be easily modified. Melting temperature can be modified to either be below or above 100° C depending on the types and concentrations of ions present19.

Physical & Chemical Characteristics:

Gellan gum has an outstanding flavor release, high gel strength, an excellent stability, process flexibility and tolerance, high clarity, excellent film former, low use level, thermally reversible gel19.

Heat and pH stable (pH 3.5 – 10). (gellan gum)

Description20

Off white powder

Formula weight

70,000 daltons with 95% 500,000 daltons

Bulk density

Approximately 836 kg/m3

Solubility20

Soluble in water, forming a viscous solution; insoluble in ethanol

pH (1% solution)21

Neutral

Moisture content

98.6%wb or 67.6% db

Loss on drying20

Not more than 15% (105°, 2½h)

Gel strength

550-850 (gm/cm)

Specific gravity

<1

Stability21

Stable at room temperature

Nitrogen20

Not more than 3%

Isopropyl alcohol20

Not more than 750 mg/kg

Microbiological criteria20

Total plate count: Not more than 10,000 colonies per gram

E. Coli: Negative by test

Salmonella: Negative by test

Yeasts and moulds: Not more than 400 colonies per gram

Rheological properties of gellan polysaccharides:

Gellan gum is one of the most interesting in situ gelling polymers that have been tested since it seems to perform very well in humans23, 24. Studies shown that residence time of gels are dependent on their rheological properties25, 26. Deacetylated gellan gum gels upon instillation in the eye due to the presence of cations27. Most rheological studies made on in situ gels use the viscosity of the gel as the rheological parameter28. When high shear is applied to gel for measurement of viscosity, it destroys structure of gel. By using oscillatory measurements, where the oscillating amplitude is small enough, the gel structure remains intact during measurements. From Oscillating measurements, the shear strain, the stress and the phase angle are determined, the parameters obtained are the complex modulus, G*, and the phase angle δ. The elastic modulus, (G’), the viscous modulus (G”) and the dynamic viscosity (η’) are calculated by:

G’ = G* cos(δ);           G” = G* sin(δ);           η’ = G”/ω

Where ω is the angular frequency, which was varied from 0.001 to 20 Hz.

Table 1. Viscosity (Pas) of Gellan gum solutions in ultra-pure water at 20˚C at different shear rates.

Sample

Shear rate (s-1)

0.0116

1.16

116

Gellan gum

0.4%

0.6%

0.8%

1.0%

 

33

160

290

360

 

0.92

2.9

5.4

8.9

 

0.031

0.13

0.15

0.33

Table 2.Viscosity of  Gellan gum versus that of xanthan gum under various conditions29.

Parameter

Viscosity (cP)1

Gellan gum (4.0 g/liter)

Xanthan gum (4.0 g/liter)

Temp (ºC)2

30

60

70

90

pH3

2

4

6

8

10

NaCl (g/liter)

0

25

50

 

4,200

4,150

4,200

4,200

 

4,100

4,120

4,150

4,200

4,200

 

4,180

4,205

4,210

 

750

580

290

193

 

365

780

775

780

680

 

740

760

780

1 Viscosity was measured at a spindle speed of 10 rpm

2 Polymer solutions were maintained at the given temperature for 1 h.

3 The pH of the solutions was adjusted with 1.0 N NaOH or 1.0 N HCl

Toxicological studies of Gellan Gum(30-40):

Acute toxicity30, 31                                                                                                     

Species

Sex

Route

LD50 (mg/kg b.w.)

Rat

M&F

M&F

Oral

Inhalation

>5000

>5.09 mg/l

Gellam gum is practically non-toxic to rats when administered as a single large dose (5 g/kg b.w.) in diet or via gavage.

Short-term studies

Rat32

Male and female Sprague-Dawley rats (20/sex/group) were fed dietary levels of Gellan Gum ranging from 0-6% for 13 weeks.  Although the animals on this study experienced symptoms of a sialodacryoadenitis viral infection, all animals survived treatment and there were no adverse effects associated with the feeding of Gellan Gum.

Monkey33

Prepubertal rhesus monkeys (2/sex/group) were dosed by oral gavage with Gellan Gum at levels of 0, 1, 2 or 3 g/kg/day for 28 days. There were no overt signs of toxicity reported.

Long-term/carcinogenicity studies

 Mouse34

Groups of 50 male and 50 female Swiss Crl mice were fed Gellan Gum admixed in the diet at 0, 1,0, 2.0 and 3.0% for 96 and 98 weeks for males and females, respectively.  All animals were examined twice daily for mortality and morbidity.  Physical examination for the presence of palpable masses was initiated on a weekly basis starting in week 26.  Bodyweights and food consumption were measured for 7-day periods on a weekly basis for the first 26 weeks of treatment and every 2 weeks thereafter.  There were no effects attributable to the feeding of Gellan Gum on either body weight gain or food consumption.  There were no neoplastic or non-neoplastic changes which were associated with the feeding of Gellan Gum.

Rat3

Groups of 50 F1 generation Sprague-Dawley rats of each sex were exposed to Gellan Gum in utero and continued on Gellan Gum diets for approximately 104 weeks.  The dietary levels of Gellan Gum were 0, 2.5, 3.8 and 5.0%. The authors concluded that in spite of the initial bodyweight deficit, the growth pattern for these treated groups was identical to that of the control.  In addition, this effect was not seen in either the females or any other species tested.  There is no basis to suggest that the lower bodyweights, observed in the male rats, are indicative of toxicity. The authors concluded that under the conditions of this bioassay, Gellan Gum was non-carcinogenic to Sprague- Dawley rats.

Dog4

Diets containing 0, 3, 4.5 and 6% Gellan Gum were fed to groups of 5 beagle dogs per sex for a period of 52 weeks. All animals survived treatment.  Food intake was higher in the treated groups compared to the controls.  There were no adverse effects associated with the feeding of GELLAN GUM to beagle dogs for a period of one year.

Reproduction studies35:

Groups of 26 male and 26 female CD (Sprague-Dawley) rats were administered Gellan Gum in their diets at doses of 0, 2.5, 3.8 or 5.0%.Males were treated for 70 days prior to mating and for three weeks after mating.  Females were treated for 14 days prior to mating and throughout mating, gestation and lactation. There was no treatment-related effect on mating or fertility index, conception rate, length of gestation, length of parturition, number of live pups, number of dead pups, post-implantation loss index, survival index on day 4, 7, 14 or 21 or lactation index for any of the generations.

Teratology studies36

Gellan Gum was fed to groups of 25 pregnant female Sprague-Dawley rats at dietary levels of 0, 2.5, 3,8 or 5.0% during days 6-15 of gestation.  Gellan Gum had no fetotoxic or teratogenic effects on rats when ingested in the diet at levels up to 5.0%.

Genotoxicity studies37-39

Test system

Test object

Concentration of gellan gum

Results

Ames test (1)

  

DNA repair test

 

V-79/HGPRT

S. typhimurium

  

Rat hepatocyte

 

Chinese hamster lung fibroblasts

10, 30, 100, 300 and 1000

 

3, 5, 10 & 20 mg/ml

 

3, 5, 10 & 20 mg/ml

Negative

  

Negative

 

Negative

 

(1) Both with and without rat liver S-9 fraction.

Observations in humans40

Five female volunteers and five male volunteers, all normal in health and free from gastrointestinal disease, participated in the clinical study.  Following a 7-day control period, each of the volunteers consumed the test substance at a daily dose level of 175 mg/kg for 7 days, then the dose was increased to 200 mg/kg/day for a further 16 days.The authors concluded that the ingestion of gellan gum at the given dose levels caused no adverse dietary nor physiological effects in any of the volunteers on the study.  There were no allergenic nor other subjective untoward manifestations, reported by or observed in any of the human subjects.  The ingestion of gellan gum, at the stated daily intake levels, did not cause any adverse toxicological effects.  However, gellan gum does act as a faecal bulking agent, increases faecal bile acid, decreases faecal neutral sterols, and decreases serum cholesterol.

Applications of gellan gum:

Due to its good rheological characteristics, gellan gum is a bacterial polysaccharide with great commercial potential for food, pharmaceuticals, and particularly environmental bioremediation. There are reports that gellan gum can be used in the bioremediation of contaminated soils and aquifers41- 44.

Applications in food industry45, 46 :

Gellan gum is a food additive that functions as a stabilizer, thickening agent, structuring and versatile gelling agent in a wide variety of foods and can produce gel textures in food products ranging from hard and brittle to fluid. Types of food products that typically contain gellan gum  include: bakery fillings, confections, dairy products, dessert gels, frostings, icings and glazes, jams and  jellies, low-fat spreads, microwavable foods, puddings, sauces, structured foods, and toppings47.

Water-based dessert gels48 are popular throughout the world and have a range of textures. Gellan gum can furnish textural diversity in these products coupled with outstanding flavour release. Small amounts of gellan gum can be used in gelatin desserts to improve heat stability and raise the setting temperature so gels will set without refrigeration. Gellan gum also improves the heat stability of other gelled products prone to melting when exposed to high ambient temperatures.

Savoury gels or aspics sometimes are used in specialty meat, fish and vegetable products to provide added appeal and succulence. Gellan gum can be used wholly or partly in place of gelatin to improve the characteristics of the aspic.

In fruit-based products49, gellan gum offers robustness during processing, provides good product stability during transportation and storage, and through its characteristic gel texture and low-concentration requirement, creates products with excellent taste and appearance.

In fruit fillings for bakery products, use of gellan gum can provide additional structure and reduction of starch levels. The added structure, coupled with the ability of the pastes to partially recover structure after shearing and depositing, results in fillings that retain water and show good bakefastness.

Since high solids products such as gelled confections are made by heating and cooling, gellan gum often can be used in their manufacture without process modifications. By using gellan gum in combination with the appropriate starch, it is possible to reduce the set time of starch jellies so they can be removed more quickly from the starch moulds. Gellan gum can also be used to impart increased heat stability to gelatin confections, resulting in products that store better at high ambient temperatures.

In decorative icings, frostings and glazes for baked goods, benefits obtained from gellan gum include good shelf stability, moisture retention, spreadability, sheen, texture and flavour release.

In South East Asia, texture is a very important characteristic and desirable texture is as important as flavour. Drinking jellies are very popular and gellan gum fluid gel technology is often used in these products.

The use of gellan gum in emulsions and cakes illustrates that it is not solely a gelling agent but can also be used in applications where structure and stability, rather than gel formation, are required.

Gellan gum also may be used in canned cat and dog food50

Applications in personal care:

In cosmetic applications,  gellan gum can be used in lotions and creams, make-up, face masks and packs, hair care products, toothpaste, and air freshener gels and providing body, stability and pleasing skin feel. Gellan gum can provide effective stabilisation and suspension of shampoo and conditioner formulas. It is ideally suited to products requiring a pseudoplastic (shear thinning) rheology.

In creams and lotions, the high yield value of gellan gum fluid gels effectively stabilises these emulsions and imparts a 'light and silky' feel when rubbed on the skin. Gellan gum also keeps emulsions stable during temperature fluctuations, for consistent quality in transit, as well as on the shelf.

In suntans and sunscreens, gellan gum stabilises the oil phase and delivers the important ingredients to the skin in a uniform manner. Gellan gum offers excellent stability over the wide range of temperatures that these products experience.

In toothpaste formulations gellan gum is beneficial both for its binding properties and its reversible, non-stringy, true-gel structure. It provides excellent flavour release, so significant reductions of flavour and sweetener levels are possible. At typical use levels, gellan gum contributes very little viscosity during toothpaste preparation allowing the design of fluid formulations that subsequently form a gel after packaging. This low viscosity performance makes manufacturing and packaging easier and allows the incorporation of fragile ingredients such as encapsulated flavours that would not normally be possible with typical binder systems. Blends of low and high acyl gellan gum can produce toothpastes with a variety of binding, stand-up and preparation viscosity.

Applications in Pharmaceutical Industry:

Gellan gum can be used to produce easy-to-swallow solid dosage forms, such as gels and coated tablets, and to modify the rate of release of active ingredients from tablets and capsules. Gellan gum is also conveniently used for controlled or sustained release of various drugs (54- 58) and also for microencapsulation preparation59. The bioavailability of theophilline from the gellan gels increases 4-5 folds in rats and 3 folds in rabbits compared to a commercial sustained release liquid dosage form6.

Applications in biotechnology Industry:

Gellan gum can be used as an alternative to agar for microbiological media11, 46, and as a bacterial growth media51, 52. It is also ideal medium for plant tissue cultivation23, 53.  It is particularly useful for the culture of thermophilic microorganisms, as the gels are thermostable and can withstand prolonged incubations at high temperatures. In addition, acceptable gel strengths can be obtained using gellan gum at a lower level than agar, and spreader colonies do not become too large. In these microbiological media applications, the high purity of gellan gum and the water-like clarity of the gels are distinct additional advantages.

In plant tissue culture, gellan gum offers a promising alternative to agar because of its purity. Gellan gum used at one-fifth the agar use level, resists contamination by moulds, is easily washed from the plant tissue for transplanting, and allows clear observation of root and tissue development.

It is extremely effective at low use levels and forms solid gels at concentrations as low as 0.1%. These are prepared by adding an electrolyte (e.g., a salt, an acid or an anionic surfactant) to a hot gellan solution and then cooling. Air freshener gels are transparent, have a high melting temperature and may contain high levels of fragrance.

In air fresheners, gellan gum enables air freshener gels of crystal clarity to be formulated. The high melting temperature of these gels makes them suitable for use in hot environments, such as cars.

Detailed description of gellan gum products in various fields22:

1) Starch-based products (fruit fillings, etc.)

This product contributes to increase of stability of starch paste, improvement of structural quality, and reduction of the amount of starch required. If left after pasting, the paste's property of partially restoring the structure and improvement of structural quality will allow the fillings to suck up water, resulting in rapid baking effect. This advantage can be applied in making the pie, pastry, and dual-pie.

2) Gel products (Dessert gel, etc.)

With only the gellan gum or combination with other conventional gelatin component, various products with heat stability and excellent emanation of odor can be manufactured. Further, use of the gellan gum will increase the setting temperature, which enables easy setting without refrigeration. If the gellan gum is added to a product with tendency of being melted when exposed to high temperature in the course of distribution and storage, heat stability of the product can be greatly improved.

3) Beverage

Gellan gum as fluid gel - Gellan gum can be used as a unique suspending agent. Gels occur when hot gellan gum solutions are allowed to cool and set under quiescent conditions. However, with low concentrations of gellan gum, shearing the gel results in the formation of pourable fluid masses with very short, flowable texture. These systems, commonly known as fluid gels, can have a wide range of textures and can exist as a light pourable gel or a thick, spreadable paste.

Gellan gum fluid gels have a high low-shear viscosity, providing remarkable suspending properties at low gum concentrations. With highly pseudoplastic, or shear thinning flow properties, application of an external shear reduces the apparent viscosity significantly. Fluid gels made from gellan gum also have a true yield stress, which imparts excellent suspension properties22.

With employment of the fluid gel technology, various beverage products can be stabilized. Small amount of the gellan gum (0.04∼0.3%) is required for preparation of the fluid gel and maintenance of the suspension status with excellent low-viscosity. Further, the gellan gum improves the feeling when drinking an orange beverage, prevents settlement of dietary fiber, and enables production of transparent beverage products. The fluid gels, which are filled at high temperature and cooled down so as to form very fragile gels, can be broken if the bottle is shaken. Such fluid gels can be used in the manufacture of the lemonade, chocolate milk, fruit juice beverage, juice, soft drink, low-fat/fat-free dressing, sauce, fermented milk, ice cream, and topping.
In addition, beads with various colors and flavors can be prepared and used in the manufacture of beverage. To prepare such beads, the gellan gum solution is dropped into an ion-rich flavor system (diffusion setting method). Carbonated beads also can be made by adding calcium carbonate into the gellan gum solution and dropping the solution into citric acid solution or fruit juice. The acidic juice will promote the gelation process and dissolve calcium carbonate to generate carbon dioxide, which is positioned inside the beads.

4) Dairy products

If the gellan gum is added to milk, and then heated and cooled down, the gellan gum makes the gel of unique structure. In manufacture of various dairy products, such as ice cream and yoghurt, the gellan gum acts as a stabilizer to help formation of gel. The gellan gum's heat stability and low viscosity at high temperature are useful in manufacturing a product going through heat treatment, such as UHT or HTST.

5) Adhesion systems

Use of the gellan gum enables easy preparation of fat-free adhesion system. If the gellan gum solution is sprayed on various foods, such as the cracker, cookie, pretzel, potato chip, and rice cake, and then various seasoning flavors and other materials required for adhesion are sprinkled, a product with greatly reduced fat concentration can be manufactured.

6) Jam/Jelly (Low sugar jam, jelly, etc.)

Since high methoxyl pectin requires careful adjustment of pH and high concentration of sugar, it cannot be used for manufacture of low solid contents products. Also, low methoxyl pectin or kappa-carrageenan causes various problems relating to storage and stability. However, the gellan gum provides stability during processing and storage, and use of only small amount results in gels with excellent taste and appearance.

7) Film and coating

The gellan gum can be used for preparation of useful films or coating in the course of making batter or breading of chicken, fish, cheese, potato, egg roll, and pizza roll. The films can be formed by spraying the hot solution of gellan gum on the surface of food, immersing the food in such hot solution of gellan gum and then cooling it down, or immersing the food in the cold solution of gellan gum. Such film formed makes a membrane that reduces oil absorption, enabling longer maintenance of crunch structure after oil-frying or baking.
Breading can be performed by spraying the gellan gum solution or immersing in the solution and then slight frying or freezing. If the foods with such breading are heated in a microwave range or an oven, they appear to be freshly fried in oil, producing low-oil foods.

Conclusion:

The large variety of applications as well as the steadily increasing number of research workers engaged in studies of Gellan gum due to their unique properties, have made significant contributions to many types of formulations and suggest that the potential of Gellan gum as novel and versatile will be even more significant in future.

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About Author:

Jigar N. Shah

Mr. Jigar N. Shah is currently working as Lecturer at Nirma Institute of Pharmacy, Dept. of Pharmaceutics & Pharm. Technology, Nirma University, Ahmedabad, Gujarat. His current job responsibilities include teaching UG classes as well as doing research for doctorate in Pharmacy from Gujarat University. He presented his research work in a number of National conferences. His research interests include Ocular Drug Delivery Systems, Nanotechnology and Transdermal Drug Delivery Systems. He is a Life Member of Association of Pharmaceutical Teachers of India.

Dr. Girish K. Jani is currently working as Professor & Principal, Dept. of Pharmaceutics, at the K. B. Raval College of Pharmacy, Shertha, Gujarat, India. He has 34 years of teaching and research experience and published 15 research papers in International and National Journals, guided 3 Ph. D. students, 35 M. Pharm. Students. He wrote various books on Pharmaceutics and Biostatistics. His research interests include Novel Drug Delivery System & Nanotechnology.

Dr. Jolly R. Parikh is currently working as Assistant Professor and Head, Dept. of Pharmaceutics & Pharmaceutical Technology, at the A.R. College of Pharmacy, Vallabh Vidyanagar, Gujarat, India. She is the chairman of the board of studies in Pharmaceutics & Pharmaceutical Technology at the Sardar Patel University, Vallabh Vidyanagar. She has almost 20 years of teaching experience and is currently guiding M. Pharm. & Ph. D. students in the research area of New Drug Delivery System.

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