Thickening agent

A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering their taste; thickeners are also used in paints, inks, explosives, and cosmetics.

Thickeners may also improve the

Thickening agents can also be used when a medical condition such as dysphagia causes difficulty in swallowing. Thickened liquids play a vital role in reducing risk of aspiration for dysphagia patients.^[1]

Many other food ingredients are used as thickeners, usually in the final stages of preparation of specific foods. These thickeners have a flavor and are not markedly stable, thus are not suitable for general use. However, they are very convenient and effective, and hence are widely used.

Different thickeners may be more or less suitable in a given application, due to differences in taste, clarity, and their responses to chemical and physical conditions. For example, for acidic foods,

Types

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Food thickeners frequently are based on either

A flavorless powdered starch used for this purpose is a fecula (from the Latin faecula, diminutive of faex, "dregs").

Other polymers

Other

• brown algae
• Agar (E406, a polysaccharide obtained from red algae)
• Carrageenan (E407, a polysaccharide obtained from red seaweeds)
• Locust bean gum (E410, a natural gum polysaccharide from the seeds of the carob tree)
• Pectin (E440, a polysaccharide obtained from apple or citrus-fruit)
• Gelatin (E441, made by partial hydrolysis of animal collagen)

Commercial jellies used in East Asian cuisines include the glucomannan polysaccharide gum used to make "lychee cups" from the konjac plants, and aiyu or ice jelly from the Ficus pumila climbing fig plant.

Agar-agar produces a very clear gel with light residual taste. Gelatin sheets disperse easily with no residual taste, but powdered form may have some taste. Kappa carragreenan may include

Many thickening agents require extra care in cooking. Some starches lose their thickening quality when cooked for too long or at too high a temperature; on the other hand, cooking starches too short or not hot enough might lead to an unpleasant starchy taste or cause water to seep out of the finished product after cooling. Also, higher viscosity causes foods to burn more easily during cooking. As an alternative to adding more thickener, recipes may call for reduction of the food's water content by lengthy simmering. When cooking, it is generally better to add thickener cautiously; if over-thickened, more water may be added but loss of flavour and texture may result.

Food thickening can be important for people facing medical issues with chewing or swallowing, as foods with a thicker consistency can reduce the chances of choking, or of inhalation of liquids or food particles, which can lead to aspiration pneumonia.

Mechanical and thixotropic agents

One of the main use of thickeners is in the paint and printing industries, which depend heavily on rheology modifiers, to prevent pigments settling to the bottom of the can, yielding inconsistent results. Water based formulas would be nearly impossible with the exception of India ink and the few other water-soluble pigments, but these would have very little coverage and at best would stain wood slightly. All modern paints and inks will have some pigment added at the factory for opacity and to control the specularity of the finish, from matte to high gloss, dependent on thickener used, but more so on the size of the particles added as opacity modifier. Particle sizes of 1 µm and below will be the limit of high gloss, probably confined to luxury automotive coatings, and about 100 µm particulates will make a bumpy surface on the microscopic scale, which scatters light and makes the surface appear matte.^{[citation needed]}

Rheology modifiers in common use:

• Polyurethanes, acrylic polymers, latex, styrene/butadiene,
• PVA - polyvinyl alcohol, not polyvinylacetate which is used in adhesives such as wood glue. PVA monomers are dispersed in the paint or ink liquid at an early stage in the mix, as it does not affect rheology unless the pH is low. Boric acid is usually used to initiate polymerization after the pigment is added (the pigment "grind" stage) and dispersed, the mixture is thickened while stirring to maintain homogeneous consistency. Often this stage is problematic since air is entrained by all but the lowest shear impellers, which are inadequate for this purpose, instead antifoam additives are used to control air bubbles, which continue to be a benefit during paint application. Air entrainment during mixing is not unique to PVA—in fact hardly a formula for paint exists that doesn't at least require some care in mixing.
• Clays - attapulgite which also disperses suspensions, bentonite (both flocculating and non-flocculating), and other montmorillonite clays. Usually clays, when dry, exist as a very fine powder, facilitating dispersion and compatibility with other ingredients. Clays generally make matte surfaces, in spite of their fine particulate nature. Not only paints and inks, but other industries such as pharmaceutical, construction, and cosmetics, especially hair styling aids and facial detoxifying masks increasingly favor bentonite and attapulgite clays over other rheology modifiers, dispersion aids, opacifying fillers, antifoam, and numerous niche uses which exploit the numerous inherent qualities which have drawn artisans to this material. Clays are sustainably sourced and do not involve any egregious environmental damage, which were among the cheapest bulk materials until recently, when the pricing went up steadily, following the upsurge in its use pattern.^{[citation needed]}
• hydroxyl groups
  are substituted by other functional groups, such as methyl or propyl. The amount of substitution and molecular weight determine viscosity of the solution, assuming concentration stays the same; adding more also increases viscosity.
• Sulfonates - Sodium or calcium salts, good water retention, versatile, and highly efficient.
• Gums - guar, xanthan, cellulose, locust bean, and acacia are the main ones.
• Saccharides -
  alginate
  , sometimes called hydrocolloids, these thickeners are extremely versatile and specific in function—each has a series of grades or types which behave differently, for example kappa carrageenan will form strong gels (potassium activated) but iota carrageenan will not form gels and only thickens.
• Proteins - Casein, collagen,^[5] and sometimes albumin.
• Modified castor oil - much like cellulose, castor oil has hydroxyl groups, unlike other oils which at most have double bonds, which castor oil also has, but most substitutions occur at the hydroxyl moieties, allowing exotic derivatives with myriad properties. The most recent advances in rheology modifiers have been in this category. The BASF corporation has a new line based on castor oil derivatives, for example.
• Organosilicones - Silicone resins, dimethicones, and modified silicones simplify formulation somewhat, a borrowing from cosmetics.

All of the above rheology modifiers are used in the 0.2% to 2.0% range

Petrochemistry

In petrochemistry, gelling agents, also called solidifiers, are chemicals capable of reacting with oil spills and forming rubber-like solids.^[6] The gelled coagulated oil then can be removed from the water surface by skimming, suction devices, or nets. Calm or only moderately rough sea is required.

Flame fuel thickening compounds

Various materials are used to convert

Fuel thickeners are mostly composed of the same thickeners as polar liquids (water), due to the fact that they are "bipolar", that is, they have a polar and an apolar group. The only change is in the orientation of these groups. In the non-polar medium reverse micelle formation occurs.

Because the hydrocarbon-hydrocarbon type intermolecular interactions are the weakest, the reverse micelle is much more unstable than the normal micelle. The main gelled fuel precursors are commonly derived from weak acids and strong or weak bases.

• Calcium acetate
• Soap
• Poly(methyl methacrylate)
• Polystyrene
• Paraffin wax
• Silicon dioxide (some grades)
• Natural rubber
• Sulfur (polysulfides)
• Polybutadiene
• Asphalt
• Bentonite clay
• Metallic soaps
• Cellulose derivatives
• Carbomer
• Alginate

See also

• Mucilage

References