Applications in foods
Table below illustrates the potential application of gellan gum in various food products. Gellan gum is not only applicable in foods, which require a highly gelled structure, but may also be suitable for uses in systems to provide body and mouth-feel rather than gelatin. In some products, it may be desirable to use gellan gum in combination with other hydrocolloids like locust been gum, xanthan gum, guar gum and modified starches to obtain optimal product texture and stability.
Confectionery
Gellan gum can be utilized in confectionery and bakery products. The major function of gellan gum in confectionery products is to provide structure and texture to reduce the set time of starch jellies. Starch jellies normally take 24 to 48 h to set, while the introduction of gellan reduces setting time to 10–12h. In addition, gellan can prevent moisture fluctuations in sugay foods, icings and toppings, and the required gellan gum concentration in these products is only one fifth of the commonly used agar .
Water based gels
Gellan gum provides dessert gels with mouth-feel characteristics similar to those of gelatin. The use of high clarity gellan gum is preferred in this application and results in a gel with clarity of water. This is highly desirable in meat and vegetable aspic. Moreover, the increase of melting temperature due to addition of gellan gum helps such gels to remain soft and juicy without melting and loosing their visual appearance. For these types of applications, a level of around 0.3 % gellan gum was found to be ideal.
Jams and jellies
Gellan can successfully replace pectin in jams and is effective at lower concentrations (about 0.4 % of gellan as compared to about 0.6 % of high methoxypectins and 0.8 % of low methoxypectins). In these products, syneresis is minimized, while jams have good organoleptic characteristics and good spreadability. Low solid and reduced calorie jams with excellent sheen can be prepared with only 0.15 % of clarified gellan.
Pie fillings and puddings
Gellan gum can be used as a structuring agent to partly replace starches in pie fillings and puddings. Alternatively, gellan in mixture with modified starches can be used as a stabilizer and water-binding agent , preventing the 'blunting effect' starches can have on food flavour.
Fabricated foods
Fabricated fruit pieces or meat chunks, including pet food, fall into this category. Many gums have been used to provide a structured form after heating and cooling . Since the gellan gum provides matrix which does not melt during pasteurization, the pieces retain their characteristic shape under the processing conditions. For this, a level of 0.7 % gellan is required in contrast to 1 % needed with carrageenan/locust been gum.
Dairy products
Negatively charged hydrocolloids like gellan or carageenan interact with the positively charged milk proteins, leading them to precipitate. The effect is undesirable when homogenous solutions/gels of milk proteins and gellan are required, and can be averted if hydrocolloids are pretreated to neutralize their negative charge. However, in other dairy products like cheese, the interactions of gellan with milk proteins, especially casein and whey lactoglobulins, increase the total yield of cheese and reduce the loss of solids (mainly proteins) in whey. Also, water retention during cheese making was enhanced after the addition of gellan to milk. The used levels of gellan gum are again very low (250–750 ppm).Ice cream is another dairy product that can be improved by the addition of gellan, where it acts as an effective bulking agent.
Pet foods
A wide variety of pet foods are commercially available in dry, semisolid or canned form. Gelling polysaccharides are generally used for solidification of certain canned products. The purpose of gelling polysaccharides in these cases is to provide continuous matrix, which retains the shape during processing. Gellan gum’s gel forming properties and efficacy at low concentration levels make it an ideal material for this application.
Reduction of oil uptake during frying
The potential use of gellan gum for reducing oil uptake has been reported. Oil uptake during frying is surface phenomenon. An increased hydrophobic character of the surface would result in increased oil uptake during frying. The ability of gellan gum to reduce oil uptake can be attributed to its hydrophilic character. Bajaj and Singhal studied the use of gellan gum for reducing oil uptake in a traditional Indian deep-fat fried product called sev, which is based on chickpea flour. Addition of 0.25 % (by mass) gellan gum to chickpea flour decreased oil content of the sev by 24.6 %. Effect of the addition of gellan gum on texture of dough and sev was also studied. Addition of gellan gum significantly .altered the texture of dough, but not the texture of sev.
Applications in pharmaceutical industry
The potential role of gellan in controlled drug release and adsorption in stomach has also been examined. Wataru et al. studied sustained delivery of paracetamol by gellan and sodium alginate formulations, and reported that the bioavailability of paracetamol from the gels formed in situ in the stomach of rabbits following oral administration of the liquid formulations prepared from gellan gum and sodium alginate was similar to that of a commercially available suspension containing an identical dose of paracetamol.
Use of gellan gum for controlled bioavailability of ophthalmic formulations has also been proposed. Sanzgiri et al. have shown that gellan-based ophthalmic solutions have longer residence time in tear fluid than saline solution. Sidda et al. formulated in situ gellan gum-based gels with ciprofloxacin hydrochloride as a drug and studied their diffusion characteristics.
The gel formulation containing both ciprofloxacin and gellan gum showed a prolonged drug release pattern. Gellan gum was evaluated as a binding agent in lactose-based tablets containing metronidazole or paracetamol. The binding properties of the gum were compared with acacia and gelatin. Granules were prepared by the conventional wet granulation method.
The results indicated that though the hardness of tablets containing gellan gum was lower than that containing gelatin or acacia, gellan gum can be employed in the formulation of normal release of metronidazole and paracetamol with moderate hardness, low friability and good disintegration and dissolution properties.
Solid culture media for growth of microorganisms and plants
A clarified grade of gellan is used as an agar substitute to solidify nutrient media for growth of microorganisms. The product withstands several autoclave cycles and is also resistant to a variety of enzymes. It has a texture that resembles that of agar. As against 15 g/L of agar, the required concentration of GelriteTM is only 6 g/L of the medium. There is also evidence that gellan gum is an ideal medium for plant tissue culture . GelriteTM media showed superior shoot proliferation, rooting and embryogenesis when compared with agar medium.Phytagel™ is an agar substitute, which is manufactured by Sigma, USA, by using gellan gum. It produces a clear, colourless, high-strength gel, which aids in the detection of microbial contamination. It is an economical alternative to agar as a gelling agent. Arregui et al. compared Phytagel™ with Difco bacto agar for in vitrotuberization of six potato cultivars. Chemical analyses of both gelling agents revealed a higher mineral content and organic impurities in Difco bacto agar than in Phytagel™, which is therefore recommended for microtuber production.
Gel electrophoresis in biological research
Gels of gellan can be used as a solid matrix for separating DNA fragments on the basis of size by electrophoresis. Gel electrophoresis is a widely practiced and key procedure in molecular biology. Gellan-based electrophoresis gels must include a second polymer such as hydroxymethylcellulose or polyethylene oxide to reduce electroosmosis. In this application gellan can replace highly refined agarose, which is very costly and used at about 1 %. By contrast, gellan costs much less than agarose and is required only at 0.125 %.
Cell immobilization
Camelin et al. found gellan gels to provide a mechanically stable matrix for the immobilization of Bifidobacterium longum (gels were stable for over 150 h of fermentation of a whey medium). In addition, biocatalyst activity (lactic acid production) was very high corresponding to the values reported by Bifidobacterium longum entrapped in carrageenan/locust bean gum.
Wenrong and Griffiths evaluated the ability of the gellan–xanthan beads to protect bifidobacteria under different conditions including peptone water, pH=4.0, pasteurized yogurt, and simulated gastric juice and they found that immobilization of bifidobacteria in beads of gellan–xanthan gum mixtures increased their tolerance of high acid environments. This approach may be useful for use of gellan gum in delivery of probiotic cultures to the gastrointestinal tract of humans.
Wenrong and Griffiths evaluated the ability of the gellan–xanthan beads to protect bifidobacteria under different conditions including peptone water, pH=4.0, pasteurized yogurt, and simulated gastric juice and they found that immobilization of bifidobacteria in beads of gellan–xanthan gum mixtures increased their tolerance of high acid environments. This approach may be useful for use of gellan gum in delivery of probiotic cultures to the gastrointestinal tract of humans.
Uses of gellan gum in microencapsulation techniques
Gellan gum can be used for the encapsulation of cultures for wastewater treatment. Moslemy et al. demonstrated that encapsulation of activated sludge in gellan gum microbeads enhanced the biological activity of microbial populations in the removal of gasoline hydrocarbons.
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