Source
Gellan gum (E418) is a bacterial exopolysaccharide, discovered through the screening of thousands of bacteria and prepared commercially by aerobic submerged fermentation from Sphingomonas elodea (previously called Pseudomonas elodea) [502], in a manner similar to xanthan. discovered in 1978,1988 Approved in Japan,1992 USA full approval.Approved throughout Asia, (except India).;`
Structural unit
Gellan gum is a linear tetrasaccharide.
?4)-L-rhamnopyranosyl-(a-1?3)-D-glucopyranosyl-(b-1?4)-D-glucuronopyranosyl-(b-1?4)-D-glucopyranosyl-(b-1? with O(2) L-glyceryl and O(6) acetyl substituents on the 3-linked glucose. It has high molecular weight, consisting of about 50,000 residues and is normally de-esterified by alkali treatment before use in food.
Gellan Gum: (C6H7)5(CH2OH)2(OH)7(O)3(CH)(CH3)
Molecular structure
Gellan gum forms a coaxial triangular 3-fold double helix (pitch 56.4 ?) from two left-handed chains coiled around each other with the acetate residues on the periphery and glyceryl groups stabilizing the interchain associations. Hydrogen-bonds are formed between the hydroxy methyl of 4-linked glucosyl units of one chain and the carboxylate group of other. There are ion-binding sites by both carboxylate oxygen atoms and a hydroxyl group in one chain and two hydroxyl groups in the other plus one strongly-bound water molecule. Pairs of helices may form antiparallel junction zones with Ca2+.
Functionality
The functionality depends on the degree of acylation and the ions present. If left acylated, gellan forms soft, elastic, transparent and flexible gels but once de-acylated it forms hard, non-elastic brittle gels. A gellan gum solution may invisibly hold particles in suspension but, unlike other gelling agents, without significantly increasing the solution's viscosity. As firm but brittle gels, they crumble in the mouth to cleverly mimic the 'melting in the mouth' sensation sensation with the release of water and associated flavors from the weak gel network.
A gel sol transition occurs at about 50°C dependent on concentration. Thermoreversible gels form on cooling in the presence of cations even at low (0.1% w/w) to very low (0.005% w/w) concentrations.
A multi-functional gelling agent
Gellan gum 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. This multi-functional gelling agent can be used alone or in combination with other products to produce a wide variety of interesting textures.
Gellan gums are available in two types - high and low acyl content:
Low acyl products form hard, non-elastic, brittle gels
High acyl products form soft, very elastic, non-brittle gels
Varying the ratios of the two forms of gellan gum produces a wide variety of textures
Structure of two types of gellan gum
The molecular structure of gellan gum is a straight chain based on repeating glucose, rhamnose and glucuronic acid units. 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 repeats. The high acyl form produces soft, elastic, non-brittle gels, whereas the low acyl form produces firm, non-elastic, brittle gels.
Fluid gels applications
Gellan gum can also 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 properties.
Potential applications include personal care, pharmaceutical and industrial suspensions.
Application
Gellan gum is widely used in foods and various other fields.
(1)Typical foods prepared using gellan gum: Gelled desserts, jam, jelly, pudding, confectionery, sugarcoating of confectionery, frost of cake, filling of cake or bread, and other foods, cakes, and pet foods.
(2) Other applications:
Microbiological media, capsules, perfumes, etc.
(3) Detailed description:
1) Starch-based products (fruit fillings, etc.)
In addition to the advantages as shown in jam and jelly, 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
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) High solid contents products
If the gellan gum is used together with starch, the set time for starch jelly is reduced, enabling quick separation from the mold. Also, when making various cakes, it provides excellent structural quality, maintenance of odors, improvement of term of use, water-holding capacity, spreadability, and gloss.
7) 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.
8) 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.
