Source of Gellan Gum
Many microorganisms in growth and metabolic processes can synthesize amorphous mucus attached to cell surface or secreted into extracellular solution, namely microbial extracellular polysaccharide (Exopolysaccharide, EPS), also called microbial metabolic glue. In recent years, with its safety, no toxicity, excellent physicochemical property and other characteristics, microbial extracellular polysaccharide attracts more and more attention of the food, pharmaceutical, cosmetics and many other industries. So far, microbial extracellular polysaccharide, which has been put into mass production, mainly includes xanthan gum, gellan gum, cardlan, dextran, pullulan, scleroglucan, etc., but the microbial polysaccharide allowed to be used as food additives by the international food legislatures is xanthan gum and gellan gum so far.
Gellan gum is another microbial extracellular polysaccharide after xanthan gum successful developed by Kelco (USA), was once called heteropolysaccharide PS-60 discovered in the end of 1970s, and there was no report about the successful lab-scale fermentation and production of gellan gum until 1982.
Sphingomonaspaucimobilis ATCC 31461, the producing strain of gellan gum, which was once called Pseudomonas eloder ATCC 31461, is an aerobic gram-negative bacterium separated from plants. With glucose, sucrose, maltose and other saccharides as carbon sources, it can grow in the culture medium containing inorganic or organic nitrogen source, phosphate and trace elements, and its optimum culture temperature is 30℃.
Characteristics and Efficacy of Gellan Gum
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Characteristic
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Efficacy
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1. High-quality gel can be formed in low concentration (0.05-0.25%).
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Gellan gum is a very effective gelling agent.
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2. It is very stable under heating and low-pH conditions.
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1) heating sterilization has little effect on gel;
2) the shelf life of acidic gel is quite long.
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3. Gel formed from sodium or potassium ions can be restored after heating while magnesium or calcium salt gel is unable to be restored.
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Thermally reversible gel and thermally irreversible gel can be made respectively.
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4. It can be smoothly compatible with other types of glue, such as the mixture of starch, xanthan gum, robinia bean glue and carrageenan
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Organizational structure can arbitrarily change from being crispy to being elastic.
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5. It has good compatibility with other ingredients.
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It can be widely applicable to all kinds of formulae.
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6. Gellan gum can form gel at a pH between 3.5 and 7.0.
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Both high-quality gel and expected gel strength can be obtained in acidic to neutral food formulae.
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7. It has aging resistance.
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It has the functions of inhibiting aging and viscosity rise to corn and other starch paste in storage.
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8. It’s not easy to cause enzymolysis.
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It provides good flexibility for food processing, and has excellent characteristics in microbiological culture media and plant tissue culture.
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Classification and Molecular Structure of Gellan Gum
Gellan gum is an anionic linear polysaccharide with the molecular weight as high as 1.5*106 Dalton. Understanding its structure from molecular level will help people apply it better.
The basic structure of gellan gum is a main chain consisting of repeated tetrasaccharide units, as shown in Figure 1. Monosaccharides participating in formation are glucose, glucuronic acid and rhamnose in the molar ratio of 2:1:1. In the natural forms of the polysaccharide, each unit has about 1.5 O-acyl groups in which there is both O-acetyl substituent and O-glyceroyl substituent, wherein the quantity of the latter is larger than that of the former. Glyceroyl is located in the Position 2 of glucose residue of 3-connection bond while acetyl is in the Position 6. O-acyl is very easy to remove through alkali so as to get the products in the acyl-removed form from natural-form gellan gum, as shown in Figure 2. By contrast, natural-form gellan gum can also be called high-acyl product.
Molecular Structure of Low-Acyl Gellan Gum (Figure 1)
Molecular Structure of High-Acyl Gellan Gum (Figure 2)
Molecular Stereoscopic Configuration of Low-Acyl Gellan Gum
Production of Gellan Gum
It is a long history to produce microbial polysaccharides with practical use value by means of fermentation. The polysaccharides extensively studied include glucan made by Leuconostoc mesenteroides, bacterial alginate made by Pseudomonas sp., xanthan gum made by Xanthamonas compestris, heat gel made by Streptococcus faecalis, Pullulan made by Aureobasidium pullulans, hyaluronic acid made by Strptococcus equii and succinoglycan made by Rhizobium. Though the polysaccharides under commercialized production are only a tiny part of the polysaccharides which have been studied, this tiny part of polysaccharides are widely and industrially used thanks to their very good performance. Because of the great success in the development of polysaccharides like Xanthan gum, people hope to find more microbial polysaccharides with good commercial prospect.
1) Strain for Gellan Gum Production
In order to find ideal food gums, Kelco collects soil or plant samples all over the world to screen more than 30 thousand strains. The production strain for Gellan gum, which is formerly called Pseudomonas elodea and is further confirmed as Sphingomonas paucimobilis based on its r-RNA feature and its sphingosine glycolipid content, is obtained through persistent efforts. The strain is an aerobic bacillus containing xanthein and Gˉ. From the aspect of biotechnology, the Sphingomonas strains are common characterized in the capability of excreting the polysaccharides like Gellan gum, Welan gum and Rhamsan gum.
Though these strains can be separated and obtained from various environments, most Sphingomonas paucimobilis strains are obtained from the clinical samples or the environment around the hospital. The production strain for Gellan gum earliest adopted in the industry is Pseudomonas elodea which is separated from water lily.
2) Biosynthesis Pathway for Gellan Gum
The biosynthesis of microbial extracellular polysaccharides includes the synthesis of homotype polysaccharides and the synthesis of heterotype polysaccharides. And the synthesis of Gellan gum belongs to the latter. The synthesis system of heterotype polysaccharides includes five factors, namely glycon nucleotide, acyl donor, lipid intermediate, enzyme system and glycon receptor. Ligio and his partners put forward the possible pathway to the synthesis of Gellan gum repeating tetrasaccharide unit through Pseudomonas eLAdea. The glycon nucleotide as the active precursor includes UDP-glucose, TDP-rhamnose and UDP-glucuronic acid which together form the monomer donor for the synthesis of the repeating unit. The enzymes involving the synthesis of the precursor include glucosephosphateisomerase (PG1), glycophosphomutase (PGM), UDP-glucopyrophosphorylase (UGP), TDP-glucopyrophosphorylase (TGP), UDP-glcdh(UGD) and TDP-rhamnose synthetase (TRS). The metabolism of glucose by Pseudomonas elodea is mainly via the glycolytic pathway and the phosphopentose pathway.
3) Production Technique for Gellan Gum
The production of Gellan gum is carried out through the ventilated fermentation in the medium containing carbon source, organic and inorganic nitrogen sources, and right amount of microelements like phosphate. The fermentation is carried out under the condition of sterilization and strict control of ventilation amount, agitation, temperature and pH value. After fermentation, the Gellan gum product is obtained through the separation of hypha proteins via physical and chemical methods.
Quality Standard for Gellan Gum
Low-acyl Gellan Gum
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Item
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Unit
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Index Value
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Gel Strength
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g/cm2
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≥800
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Transparency
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%
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≥74
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80-mesh Fine Powder
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%
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≥98
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Loss on Drying
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%
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≤12.0
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Ash
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%
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≤15.0
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pH 1% Solution
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4-7
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Arsenic
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ppm
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≤2.0
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Lead
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ppm
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≤2.0
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Total Bacterial Count
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cfu/g
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≤10,000
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Yeast and Fungus
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cfu/g
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≤300
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Coliform Group
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MPN/100g
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Not Detected
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Pathogenic Bacteria (Salmonella)
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Not Detected
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Package: 25kg/cardboard drum
Storage: store in cool and dry place and avoid being directly exposed to sunlight
Shelf Life: 1 year
