Glycerin is an organic compound produced from oils and fats, used in food, cosmetics, and medicine. It has a syrup-like viscosity and can be used as a non-toxic antifreeze. It is produced as a byproduct of soap making and can also be made directly from vegetable oil. Glycerin is widely used in the food industry as a sweetener and to keep foods moist. It is also used in the cosmetic industry for its moisturizing properties and in medicine for cough mixtures and topical remedies.
Glycerin, also known as glycerol, is an organic compound of carbon, hydrogen and oxygen with the chemical formula C3H8O3. It is produced industrially, usually as a by-product of soap making, from oils and fats. It can be obtained from animal fat or, in the case of vegetable glycerin, from vegetable oil. The source of the raw material does not affect the chemistry of the final product, but as glycerin is used extensively in foods and medicines, this distinction is important for vegetarians. It is also used as a sweetener and as an ingredient in numerous cosmetic products.
structure and properties
The compound consists of a chain of three carbon atoms, to which hydrogen atoms are attached on one side and hydroxyl groups (OH) on the other. The three OH groups form hydrogen bonds between the molecules, giving the compound a syrup-like viscosity and allowing it to dissolve easily in water. Chemically speaking, glycerin is an alcohol, but for food purposes it is classified – in the USA – as a carbohydrate by the Federal Food and Drug Administration (FDA), because it provides calories and is not a fat or a protein.
Pure glycerol does not crystallize easily, but it can be cooled to form a solid that melts at approximately 64.4°C (18°F). Instead, it lowers the freezing point of water by an amount that depends on the concentration. For example, a 66.7% solution freezes at -51°F (-46.1°C). For this reason it can be used as a non-toxic antifreeze and for the storage of sensitive liquids, such as enzymes, in laboratory freezers.
Production
Glycerol forms the “backbone” of many lipids, i.e. oils and fats, and there are various processes that can be used to extract it from these substances. Most glycerin is produced as a byproduct of soap making. Animal fats or vegetable oils may be used in this process. It is heated with a strong alkali, usually caustic soda (sodium hydroxide), making soap and a solution of glycerin in water. This solution is then purified by distillation.
Vegetable glycerin can also be made directly from vegetable oil, often coconut or palm oil, by heating it to a high temperature under pressure with water. The glycerin backbone separates from the fatty acids and is absorbed by water, from which it is then isolated and distilled to obtain the pure product. Food grade vegetable glycerin is 99.7% pure, with the remaining 0.3% being water.
Interest in biodiesel fuel has led to the production of large quantities of low-quality, non-food vegetable glycerine as a by-product. Purification of the liquid is not considered economically feasible and cannot be disposed of casually as it contains toxic methanol, which is used in the manufacturing process. As of 2013, there is a lot of research to find a use for this substance, something that doesn’t require high purity glycerin. One promising possibility is to use it as a precursor in the production of some useful plastics.
Main uses
Glycerin is widely used in the food industry for two main reasons: it has a sweet taste, but has fewer calories than sugar; and is hygroscopic, i.e. it absorbs moisture from the air. It is therefore used both to sweeten foods and to keep them moist. The compound is metabolized more slowly than sucrose — the type of sugar most commonly found in candy and processed foods — and therefore doesn’t have as dramatic an effect on blood sugar levels. It also does not contribute to bacterial decay. Foods marketed as low-carb are often sweetened with glycerin.
Another major use is in the cosmetic industry. Due to its hygroscopic properties, it is used in many skin moisturizing products, as it appears to help alleviate dry skin problems by drawing water from the lower layers. It is also a component of glycerin soap, which is often used by people with sensitive skin. Lotions containing this compound are also popular.
Vegetable glycerin can be used as a substitute for ethanol – the chemical commonly called “alcohol” – in the production of botanical extracts, such as herbal essences. It acts as a solvent which dissolves the substances of interest from the plant raw material. The benefit of this is that people who don’t want to be exposed to alcohol can still have access to botanicals. The downside is that the resulting products have a much shorter shelf life.
There are also medical uses for vegetable glycerin. It is a common ingredient in cough mixtures, due to its soothing properties. Other applications are as a topical remedy for a range of skin problems, including psoriasis, rashes, burns, bedsores and cuts; as a laxative, in the form of suppositories; and to treat gum disease, as it inactivates the associated bacterial colonies.
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