Xanthan gum is a polysaccharide secreted by the bacterium Xanthomonas campestris, used
as a food additive and rheology modifier, commonly used as a food thickening agent and
a stabilizer.
It is composed of pentasaccharide repeat units, comprising glucose, mannose, and glucuronic
acid in the molar ratio 2.0:2.0:1.0.
It is produced by the fermentation of glucose, sucrose, or lactose.
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.
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 cytoplasmic
membrane.
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.
Preparation The polysaccharide is prepared by inoculating
a sterile aqueous solution of carbohydrate(s), a source of nitrogen, dipotassium phosphate,
and some trace elements.
The medium is well-aerated and stirred, and the polymer is produced extracellularly into
the medium.
The final concentration of xanthan produced will vary greatly depending on the method
of production, strain of bacteria, and random variation.
After fermentation that can vary in time from one to four days, the polymer is precipitated
from the medium by the addition of isopropyl alcohol, and the precipitate is dried and
milled to give a powder that is readily soluble in water or brine.
In the United States, the manufacture of one kilogram of cheese creates nine kg of the
byproduct whey, for which the USDA sought to find more uses.
Whey is composed mostly of water and lactose, so researchers developed a strain of X.
campestris that would grow on lactose rather than glucose.
The newly developed lactose-using bacteria produced 30 g/L of xanthan gum for every 40
g/L of whey powder.
Whey-derived xanthan gum is commonly used in many commercial products, such as shampoos
and salad dressings.
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.
It was brought into commercial production by the Kelco Company under the trade name
Kelzan in the early 1960s.
It was approved for use in foods after extensive animal testing for toxicity in 1968.
It is accepted as a safe food additive in the USA, Canada, Europe, and many other countries,
with E number E415.
Xanthan gum derives its name from the strain of bacteria used during the fermentation process,
Xanthomonas campestris.
X.
campestris is the same bacterium responsible for causing black rot to form on broccoli,
cauliflower, and other leafy vegetables.
The bacteria forms a slimy substance that acts as a natural stabilizer or thickener.
Uses 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.
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, wherein it serves as a binder to keep the product
uniform.
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.
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.
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
prevent washout.
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.
Amounts Used As a thickening agent, the amount of xanthan
gum you will use depends on how thick you want the liquid to be.
In general, you will use a 0.2% weight ratio for light thickening, 0.7% for a thicker sauce,
and up to 1.5% for a very thick sauce.
Be warned though, adding too much xanthan gum can result in a texture and mouthfeel
resembling mucus.
To make a xanthan gum foam a ratio between 0.2% and 0.8% is typically used.
The more xanthan gum you use the larger the bubbles that can occur and the denser the
foam will be.
For bubbles, resembling soap bubbles, a typical ratio is 0.1% to 0.4% xanthan gum and 0.2%
to 2.0% Versawhip or egg white powder.
When making an emulsion, the more xanthan gum you add, the stronger the emulsion will
be.
However, it will also thicken the emulsion, which may or may not be desirable.
To start binding an emulsion a ratio of around 0.1% can be used.
If you want to also thicken the emulsion you can add up to around 0.8% of xanthan gum.
Health
Evaluation of workers exposed to xanthan gum dust found evidence of a link to respiratory
symptoms.
On May 20, 2011 the FDA issued a press release about SimplyThick, a food-thickening additive
containing xanthan gum as the active ingredient, warning "parents, caregivers and health care
providers not to feed SimplyThick, a thickening product, to premature infants."
The concern is that the product may cause necrotizing enterocolitis.
Allergies Xanthan gum may be derived from a variety
of source products that are themselves common allergens, such as corn, wheat, dairy, or
soy.
As such, persons with known sensitivities or allergies to food products are advised
to avoid foods including generic xanthan gum or first determine the source for the xanthan
gum before consuming the food.
To be specific, an allergic response may be triggered in people sensitive to the growth
medium, usually corn, soy, or wheat.
For example, residual wheat gluten has been detected on xanthan gum made using wheat.
This may trigger a response in people highly sensitive to gluten.
Xanthan gum is a "highly efficient laxative," according to a study that fed 15 g/day for
10 days to 18 normal volunteers.
Some people react to much smaller amounts of xanthan gum with symptoms of intestinal
bloating and diarrhea.
There are many substitutes for xanthan gum when used for baking such as guar gum and
locust bean gum.
References