Athickening agent orthickeneris asubstance which can increase theviscosity of aliquid without substantially changing its other properties.Edible thickeners are commonly used to thickensauces,soups, andpuddings without altering their taste; thickeners are also used inpaints,inks,explosives, andcosmetics.
Thickeners may also improve thesuspension of other ingredients oremulsions which increases the stability of the product. Thickening agents are often regulated asfood additives and ascosmetics andpersonal hygiene product ingredients. Some thickening agents aregelling agents (gellants), forming agel, dissolving in the liquid phase as acolloid mixture that forms a weakly cohesive internal structure. Others act as mechanicalthixotropic additives with discrete particles adhering or interlocking to resiststrain.
Thickening agents can also be used when a medical condition such asdysphagia causes difficulty in swallowing. Some of these people may benefit fromthickened fluids, but the benefits are limited.[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,arrowroot is a better choice thancornstarch, which loses thickening potency in acidic mixtures. AtpH levels below 4.5, guar gum has sharply reduced aqueous solubility, thus also reducing its thickening capability. If the food is to be frozen,tapioca or arrowroot are preferable over cornstarch, which becomes spongy when frozen.
Food thickeners frequently are based on eitherpolysaccharides (starches,vegetable gums, andpectin), orproteins.[2]
This category includes starches asarrowroot,cornstarch,katakuri starch,potato starch,sago, wheat flour,almond flour,tapioca and theirstarch derivatives.
A flavorless powderedstarch used for this purpose is afecula (from the Latinfaecula, diminutive offaex, "dregs").
Othersugar polymers includevegetable gums such aspectin fromCitrus peel,guar gum from theguar bean, andlocust bean gum from thecarob bean.
Agar,alginin andcarrageenan are polysaccharides extracted from algae,xanthan gum is a polysaccharide secreted by the bacteriumXanthomonas campestris, andcarboxymethyl cellulose is a synthetic gum derived fromcellulose. Proteins used as food thickeners includecollagen,egg whites, andgelatin. Other thickening agents act on the proteins already present in a food; for examplesodium pyrophosphate, which acts oncasein in milk during the preparation ofinstant pudding.
Gelling agents arefood additives used to thicken and stabilize various foods, likejellies,desserts andcandies. The agents provide the foods with texture through formation of agel. Somestabilizers and thickening agents are gelling agents.
Typical gelling agents are based on polysaccharides such asnatural gums,starches,pectins andagar-agar or proteins such asgelatin.
Examples are:
Commercial jellies used in EastAsian cuisines include theglucomannan polysaccharide gum used to make "lychee cups" from thekonjac plants, andaiyu or ice jelly from theFicus 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 carrageenan may includepotassium chloride to improve the gelling process and produces a clear product with very little aftertaste. Iota carrageenan containssodium chloride which improves gel formation.Sodium alginate produces a medium viscosity gel but may have some aftertaste. High-methoxy pectin is one of the most widely used gelling agents infood processing. It reacts with some sugars and acids and sometimes includes minerals to improve gelling process. Low-methoxy pectin reacts with calcium, and is used for the preparation of low sugar jams.[3]
Functionalflours are produced from specific cereal variety (wheat,maize,rice or other) conjugated to specific heat treatment able to increase stability, consistency and general functionalities. These functional flours are resistant to industrial stresses such as acidic pH, sterilisation, freeze conditions, and can help food industries to formulate withnatural ingredients. For the final consumer, these ingredients are more accepted because they are shown as "flour" in the ingredient list.[4]
Flour is often used for thickeninggravies,gumbos, andstews. The most basic type of thickening agent, flour blended with water to make a paste, is calledwhitewash.[5] It must be cooked in thoroughly to avoid the taste of uncooked flour.Roux, a mixture of flour and fat (usually butter) cooked into a paste, is used for gravies,sauces and stews. Cereal grains (oatmeal,couscous,farina, etc.) are used to thickensoups.Yogurt is popular in Eastern Europe and Middle East for thickening soups. Soups can also be thickened by adding grated starchy vegetables before cooking, though these will add their own flavour. Tomato puree also adds thickness as well as flavour.Egg yolks are a traditional sauce thickener in professional cooking; they have rich flavor and offer a velvety smooth texture but achieve the desired thickening effect only in a narrow temperature range. Overheating easily ruins such a sauce, which can make egg yolk difficult to use as a thickener for amateur cooks. Other thickeners used by cooks arenuts (includingrehan) orglaces made ofmeat orfish.
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 lengthysimmering. 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 withchewing orswallowing, as foods with a thicker consistency can reduce the chances ofchoking, or of inhalation of liquids or food particles, which can lead toaspiration pneumonia.
Fumed silica and similar products form stiff microscopic chains or fibers which interlock or agglomerate into a mass, holding the associated liquid bysurface tension, but which can separate or slide when sufficient force is applied. This causes thethixotropic or shear-thinning property (also frequently exhibited by gels), where the viscosity isnon-Newtonian and becomes lower as the shearing force or time increases; their usefulness is primarily that the resulting increase in viscosity is large compared to the quantity of silica added. Fumed silica isgenerally accepted as safe as a food additive[6] and is frequently used in cosmetics. Additives such asprecipitated silica, finetalc, orchalk also meet the definition ofthickening agent in that they increase viscosity and body while not affecting the target property of a mixture.[citation needed]
Thickening agents used in cosmetics or personal hygiene products include viscous liquids such aspolyethylene glycol, synthetic polymers such ascarbomer (a trade name forpolyacrylic acid) andvegetable gums. Some thickening agents may also function asstabilizers when they are used to maintain the stability of anemulsion. Someemollients, such aspetroleum jelly and variouswaxes may also function as thickening agents in an emulsion.[citation needed]
One of the main use of thickeners is in the paint and printing industries, which depend heavily onrheology modifiers, to prevent pigments settling to the bottom of the can, yielding inconsistent results. Water based formulas would be nearly impossible with the exception ofIndia 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:
All of the above rheology modifiers are used in the 0.2% to 2.0% range
In petrochemistry, gelling agents, also calledsolidifiers, are chemicals capable of reacting withoil spills and forming rubber-like solids.[8] 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.
Various materials are used to convertliquid explosives to a gel form.Nitrocellulose and othernitro esters are often used. Other possibilities include nitratedguar gum.
Many fuels used inincendiary devices require thickening for increased performance. Aluminium salts offatty acids are frequently used. Some formulations (e.g.Napalm-B) use polymeric thickeners.Thickened pyrophoric agent, apyrophoric replacement of napalm, is atriethylaluminium thickened withpolyisobutylene.
Fuel thickeners are mostly composed of the same thickeners as polar liquids (water), due to the fact that they areamphiphile, that is, they have a polar and an apolar group. The only change is in the orientation of these groups. In the non-polar mediumreverse micelle formation occurs.[9]
Because the hydrocarbon-hydrocarbon typeintermolecular 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.
