Xanthan gum is a polysaccharide, derived from the bacterial coat of Xanthomonas campestris, used as a food additive and rheology modifier, commonly used as a food thickening agent (in salad dressings, for example) and a stabilizer (in cosmetic products, for example, to prevent ingredients from separating).
Xanthan gum is used as a thickener in sauces, as an agent in ice cream that prevents ice crystals from forming, and as a fat substitute that adds the “mouth feel” of fat without the calories. It is used in canned pet food to add “cling”.
In pastry fillings, it prevents “weeping” (syneresis) of the water in the filling, protecting the crispness of the crust. It has a very high viscosity (thickness) even when very little is used.
When mixed with guar gum or locust bean gum, the viscosity is more than when either one is used alone, so less of each can be used. The backbone of Xanthan gum is similar to cellulose, but the trisacharide side chains of mannose and glucuronic acid make the molecule rigid, and allow it to form a right-handed helix. These features make it interact with itself and with other long chain molecules to form thick mixtures and gels in water.