Xanthan gum is a polysaccharide used as a food additive and rheology modifier (Davidson ch. 24). Polysaccharides are relatively complex Carbohydrates They are Polymers made up of many Monosaccharides joined together by Glycosidic bonds Food additives are substances added to food to preserve flavour or improve its taste and appearance Rheology is the study of the flow of matter mainly liquids but also soft solids or solids under conditions in which they flow rather than deform elastically It is produced by a process involving fermentation of glucose or sucrose by the Xanthomonas campestris bacterium. Fermentation is the process of deriving energy from the oxidation of organic compounds such as carbohydrates using an endogenous electron acceptor which is Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Solubility of Pure SucroseTemperature(Cg Xanthomonas campestris is a bacterial species which causes a variety of Plant Diseases It is used in the commercial production of a high molecular weight polysaccharide The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have

Contents 1 Chemical structure 2 Preparation 3 History 4 Uses 5 Allergy 6 References and footnotes 7 External links

Chemical structure

The backbone of the polysaccharide chain consists of two β-D-glucose units linked through the 1 and 4 positions. The side chain consists of two mannose and one glucuronic acid, so the chain consists of repeating modules of five sugar units. Mannose is a Sugar Monomer of the Hexose series of Carbohydrates Metabolism Mannose enters the carbohydrate Metabolism Glucuronic acid (from Greek γλυκερός - "sweet" is a Carboxylic acid. The side chain is linked to every other glucose of the backbone at the 3 position. About half of the terminal mannose units have a pyruvic acid group linked as a ketal to its 4 and 6 positions. Pyruvic acid (CH3COCO2H is an alpha-keto acid. The Carboxylate Anion of pyruvic acid is known as pyruvate. A ketal is a Functional group or Molecule containing the functional group of a Carbon bonded to two -OR groups where O is Oxygen The other mannose unit has an acetyl group at the 6 positions. In Organic chemistry, acetyl (ethanoyl is a Functional group, the Acyl of Acetic acid, with Chemical formula - C[[Oxygen Two of these chains may be aligned to form a double helix, giving a rather rigid rod configuration that accounts for its high efficiency as a viscosifier of water. The molecular weight of xanthan varies from about one million to 50 million depending upon how it is prepared.

Preparation

The polysaccharide is prepared by inoculating a sterile aqueous solution of carbohydrate(s), a source of nitrogen, di-potassium monohydrogen phosphate, and some trace elements. Dipotassium phosphate (K2HPO4 - also phosphoric acid dipotassium salt dipotassium hydrogen orthophosphate potassium phosphate dibasic - is a highly water-soluble The medium is well-aerated and stirred, and the polymer is produced extracellularly into the medium. The final concentration of xanthan produced is about three to five percent by weight. After fermentation over about four days, the polymer is precipitated from the medium by the addition of isopropyl alcohol and dried and milled to give a powder that is readily soluble in water or brine. Isopropyl alcohol (also isopropanol, iso, isopro, Rubbing alcohol, or the abbreviation IPA) is a common name for

History

It was discovered by an extensive research effort by Allene Rosalind Jeanes and her research team at the United States Department of Agriculture, which involved the screening of a large number of biopolymers for their potential uses. Biopolymers are a class of Polymers produced by living organisms It was brought into commercial production by the Kelco Company under the trade name Kelzan in the early 1960s. (Whistler p. 486) It was approved for use in foods after extensive animal testing for toxicity in 1969. It is accepted as a safe food additive in the USA, Canada and Europe, with E number E415. Food additives are substances added to food to preserve flavour or improve its taste and appearance E numbers are number codes for Food additives and are usually found on Food labels throughout the European Union.

Uses

One of the most remarkable properties of xanthan gum is its capability of producing a large increase in the viscosity of a liquid by adding a very small quantity of gum, on the order of one percent. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. In most foods, it is used at 0. 5% and can be used in lower concentrations. The viscosity of xanthan gum solutions decreases with higher shear rates; this is called pseudoplasticity. A pseudoplastic material is one in which Viscosity decreases with increasing rate of shear (also termed shear thinning) This means that a product subjected to shear, whether from mixing, shaking or even chewing, will thin out, but once the shear forces are removed, the food will thicken back up. A practical use would be in salad dressing: The xanthan gum makes it thick enough at rest in the bottle to keep the mixture fairly homogeneous, but the shear forces generated by shaking and pouring thins it so it can be easily poured. When it exits the bottle, the shear forces are removed and it thickens back up so it clings to the salad. Unlike other gums, it is very stable under a wide range of temperatures and pH. pH is the measure of the acidity or alkalinity of a Solution.

In foods, xanthan gum is most often found in salad dressings and sauces. It helps to stabilize the colloidal oil and solid components against creaming by acting as an emulsifier. A colloid is a type of mechanical Mixture where one substance is dispersed evenly throughout another see also Cream (disambiguation Creaming may refer to In cooking and baking In cooking the process of cooking An emulsion ( IPA: /ɪˈmʌlʃən/ is a mixture of two Immiscible (unblendable liquids Also used in frozen foods and beverages, xanthan gum creates the pleasant texture in many ice creams. Toothpaste often contains xanthan gum, where it serves as a binder to keep the product uniform. Xanthan gum is also used in gluten-free baking. Since the gluten (found in wheat) must be omitted, xanthan gum is used to give the dough or batter a "stickiness" that would otherwise be achieved with the gluten. Xanthan gum also helps thicken commercial egg substitutes made from egg whites to replace the fat and emulsifiers found in yolks. It is also a preferred method of thickening liquids for those with swallowing disorders, since it does not change the color or flavor of foods or beverages.

In the oil industry, xanthan gum is used in large quantities, usually to thicken drilling fluids. The petroleum industry includes the global processes of exploration, extraction, refining, transporting (often by Oil tankers and pipelines These fluids serve to carry the solids cut by the drilling bit back to the surface. The widespread use of horizontal drilling and the demand for good control of drilled solids has led to the expanded use of xanthan gum. Directional drilling (or slant drilling) is the practice of drilling non-vertical wells It can be broken down into three main groups Oilfield Directional Xanthan gum has also been added to concrete poured underwater, in order to increase its viscosity and prevent washout. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag

In cosmetics xanthan gum is used to prepare water gels usually in conjunction with bentonite clays. Bentonite is an absorbent Aluminium phyllosilicate generally impure Clay consisting mostly of Montmorillonite. Is also used in oil-in-water emulsions to help stabilise the oil droplets against coalesence. It has some skin hydrating properties.

Allergy

Some people are allergic to xanthan gum, with symptoms of intestinal gripes, diarrhea, temporary high blood pressure, and migraine headaches. Workers exposed to xanthan gum dust exhibit nose and throat irritation as well as work-related illness, with symptoms becoming more prevalent with increasing exposure. ^[1]

Also, since xanthan gum is produced by a bacterium that is fed corn to grow, some people allergic to corn will also react to it. ^[2]

References and footnotes

External links

• Xanthan Gum, by J. Flores Candia & W. Deckwer, Encyclopedia of Bioprocess Technology, John Wiley & Sons Inc (1999)
• Xanthan Gum, by Martin Chaplin, accessed Dec 2007
• X Is for Xanthan Gum, by Lynn A. Kuntz, Food Product Design, June 2007
• VanZan Xanthan Gum, by R. T. Vanderbilt Co Inc, Sep 2007
• Rosalind Jeanes and the invention of xanthan gum, by Chemical Heritage Foundation, accessed Dec 2007

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