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).
It is produced by the fermentation of glucose, sucrose, or lactose
by the Xanthomonas campestris bacterium. After a fermentation
period, the polysaccharide is precipitated from a growth medium
with isopropyl alcohol, dried, and ground into a fine powder.
Later, it is added to a liquid medium to form the gum.
One of the most remarkable properties of Xanthan Gum is its ability
to produce a large increase in the viscosity of a liquid by adding
a very small quantity of gum, on the order of one percent. 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 shear thinning or pseudoplasticity. 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.
Biosynthesis Synthesis originates from glucose as substrate for
synthesis of the sugar nucleotides precursors UDP-glucose,
UDP-glucuronate, and GDP-mannose that are required for building the
pentasaccharide repeat unit. This links the synthesis of xanthan to
the central carbohydrate metabolism. The repeat units are built up
at undecaprenylphosphate lipid carriers that are anchored in the
Specific glycosyltransferases sequentially transfer the sugar
moieties of the nucleotide sugar xanthan precursors to the lipid
carriers. Acetyl and pyruvyl residues are added as non-carbohydrate
decorations. Mature repeat units are polymerized and exported in a
way resembling the Wzy-dependent polysaccharide synthesis mechanism
of Enterobacteriaceae. Products of the gum gene cluster drive
synthesis, polymerization, and export of the repeat unit.
In foods, Xanthan Gum is most often found in salad dressings and
sauces. It helps to prevent oil separation by stabilizing the
emulsion, although it is not an emulsifier. Xanthan Gum also helps
suspend solid particles, such as spices. Also used in frozen foods
and beverages, Xanthan Gum helps create the pleasant texture in
many ice creams, along with Guar Gum and locust bean gum.
Toothpaste often contains Xanthan Gum, where it serves as a binder
to keep the product uniform. Xanthan Gum (when sometimes not made
from wheat—see Allergies for gluten-free allergy information) 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 at typical use levels.
In the oil industry, Xanthan Gum is used in large quantities,
usually to thicken drilling mud. These fluids serve to carry the
solids cut by the drilling bit back to the surface. Xanthan Gum
provides great "low end" rheology. When the circulation stops, the
solids still remain suspended in the drilling fluid. The widespread
use of horizontal drilling and the demand for good control of
drilled solids has led to its expanded use. It has also been added
to concrete poured underwater, to increase its viscosity and
In cosmetics, Xanthan Gum is used to prepare water gels, usually in
conjunction with bentonite clays. It is also used in oil-in- water
emulsions to help stabilize the oil droplets against coalescence.
It has some skin hydrating properties. Xanthan Gum is a common
ingredient in fake blood recipes, and in gunge/slime.