Vegetable Glycerine (Glycerol)
Glycerol also called glycerine or glycerin is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in all lipids known as triglycerides. It is widely used in the food industry as a sweetener and humectant and in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature.
Glycerol is generally obtained from plant and animal sources where it occurs as triglycerides. Triglycerides are esters of glycerol with long-chain carboxylic acids. The hydrolysis, saponification, or transesterification of these triglycerides produces glycerol as well as the fatty acid derivative.
Typical plant sources include soybeans or palm. Animal-derived tallow is another source. Approximately 950,000 tons per year are produced in the United States and Europe; 350,000 tons of glycerol were produced per year in the United States alone from 2000 to 2004.
What is glycerin?
Glycerin is chemically a sugar alcohol . On the Nutrition Facts labels, it is included in total carbohydrates, and, as a subcategory, in sugar alcohols . In the EU, glycerin is listed as E number E422.
- Calories per gram = 4.3
- Glycemic index (GI) = ?
- Sweetness, relative to sucrose = 75%
- Net carbs = probably 100%
In food and beverages, glycerol serves as a humectant, solvent, and sweetener, and may help preserve foods. It is also used as filler in commercially prepared low-fat foods (e.g., cookies), and as a thickening agent in liqueurs. Glycerol and water are used to preserve certain types of plant leaves. As a sugar substitute, it has approximately 27 kilocalories per teaspoon (sugar has 20) and is 60% as sweet as sucrose. It does not feed the bacteria that form plaques and cause dental cavities. As a food additive, glycerol is labeled as E number E422. It is added to icing (frosting) to prevent it from setting too hard.
As used in foods, glycerol is categorized by the Academy of Nutrition and Dietetics as a carbohydrate. The U.S. Food and Drug Administration (FDA) carbohydrate designation includes all caloric macronutrients excluding protein and fat. Glycerol has a caloric density similar to table sugar, but a lower glycemic index and different metabolic pathway within the body, so some dietary advocates accept glycerol as a sweetener compatible with low-carbohydrate diets.
Pharmaceutical and personal care applications.
- Personal lubricants commonly contain glycerol
- Glycerol is an ingredient in products such as hair gel
- Glycerol suppositories used as laxatives
- Glycerin is often used in electronic cigarettes to create the vapor
- Glycerol is also used to power diesel generators supplying electricity for the FIA Formula E series of electric race cars.
Glycerol is used in medical, pharmaceutical and personal care preparations, mainly as a means of improving smoothness, providing lubrication, and as a humectant. It is found in allergen immunotherapies, cough syrups, elixirs and expectorants, toothpaste, mouthwashes, skin care products, shaving cream, hair care products, soaps, and water-based personal lubricants. In solid dosage forms like tablets, glycerol is used as a tablet holding agent. For human consumption, glycerol is classified by the U.S. FDA among the sugar alcohols as a caloric macronutrient.
Glycerol is a component of glycerin soap. Essential oils are added for fragrance. This kind of soap is used by people with sensitive, easily irritated skin because it prevents skin dryness with its moisturizing properties. It draws moisture up through skin layers and slows or prevents excessive drying and evaporation.
Glycerol can be used as a laxative when introduced into the rectum in suppository or small-volume (2–10 ml) (enema) form; it irritates the anal mucosa and induces a hyperosmotic effect.
Taken orally (often mixed with fruit juice to reduce its sweet taste), glycerol can cause a rapid, temporary decrease in the internal pressure of the eye. This can be useful for the initial emergency treatment of severely elevated eye pressure.
Glycerol was historically used as an anti-freeze for automotive applications before being replaced by ethylene glycol, which has a lower freezing point. While the minimum freezing point of a glycerol-water mixture is higher than an ethylene glycol-water mixture, glycerol is not toxic and is being re-examined for use in automotive applications.
In the laboratory, glycerol is a common component of solvents for enzymatic reagents stored at temperatures below 0 °C due to the depression of the freezing temperature. It is also used as a cryoprotectant where the glycerol is dissolved in water to reduce damage by ice crystals to laboratory organisms that are stored in frozen solutions, such as bacteria, nematodes, and mammalian embryos.
Glycerol is used to produce nitroglycerin, which is an essential ingredient of various explosives such as dynamite, gelignite, and propellants like cordite. Reliance on soap-making to supply co-product glycerol made it difficult to increase production to meet wartime demand. Hence, synthetic glycerol processes were national defense priorities in the days leading up to World War II. Nitroglycerin, also known as glyceryl trinitrate (GTN) is commonly used to relieve angina pectoris, taken in the form of sub-lingual tablets, or as an aerosol spray.
When utilized in “tincture” method extractions, specifically as a 10% solution, glycerol prevents tannins from precipitating in ethanol extracts of plants (tinctures). It is also used as an “alcohol-free” alternative to ethanol as a solvent in preparing herbal extractions. It is less extractive when utilized in a standard tincture methodology. Alcohol-based tinctures can also have the alcohol removed and replaced with glycerol for its preserving properties. Such products are not “alcohol-free” in a scientific sense, as glycerol contains three hydroxyl groups. Fluid extract manufacturers often extract herbs in hot water before adding glycerol to make glycerites.
When used as a primary “true” alcohol-free botanical extraction solvent in non-tincture based methodologies, glycerol has been shown to possess a high degree of extractive versatility for botanicals including removal of numerous constituents and complex compounds, with an extractive power that can rival that of alcohol and water–alcohol solutions. That glycerol possesses such high extractive power assumes it is utilized with dynamic methodologies as opposed to standard passive “tincturing” methodologies that are better suited to alcohol. Glycerol possesses the intrinsic property of not denaturing or rendering a botanical’s constituents inert (as alcohols – i.e. ethyl (grain) alcohol, methyl (wood) alcohol, etc., do). Glycerol is a stable preserving agent for botanical extracts that, when utilized in proper concentrations in an extraction solvent base, does not allow inverting or reduction-oxidation of a finished extract’s constituents, even over several years. Both glycerol and ethanol are viable preserving agents. Glycerol is bacteriostatic in its action, and ethanol is bactericidal in its action.
Glycerol is a precursor for synthesis of triacylglycerols and of phospholipids in the liver and adipose tissue. When the body uses stored fat as a source of energy, glycerol and fatty acids are released into the bloodstream. Circulating glycerol does not glycate proteins as do glucose or fructose, and does not lead to the formation of advanced glycation endproducts (AGEs). In some organisms, the glycerol component can enter the glycolysis pathway directly and, thus, provide energy for cellular metabolism (or, potentially, be converted to glucose through gluconeogenesis).
Before glycerol can enter the pathway of glycolysis or gluconeogenesis (depending on physiological conditions), it must be converted to their intermediate glyceraldehyde 3-phosphate.
Vegetable glycerin, also called glycerol, is sometimes used as a food additive in baked goods, candy, fudge, dairy products, meat, pasta, cereals, processed fruits and vegetables, condiments, soups, sauces, egg products and fish products. Sometimes it is used to help maintain moisture levels or mix oil- and water-based ingredients, but it can also be used as a sweetener. The U.S. Food and Drug Administration regards it as generally safe, though the additive can have some side effects in large amounts.
Promotes Skin Cell Maturation
Glycerin, or glycerol, can fight the effects of skin diseases such as psoriasis. Drs. Xiangjian Zheng and Wendy Bollinger Bollag explain in the December 2003 issue of the Journal of Investigative Dermatology that glycerin, when applied to the skin, signals the cells to mature in normal fashion. Psoriasis is a skin disease in which the skin cells shed too quickly, before they are properly mature, causing thickened, scaly skin. The application of glycerin can interrupt this abnormal process, and allows the cells to reach full maturation before shedding. The compound can also help wounds heal more quickly in some cases.
The small amount of vegetable glycerin used in food products isn’t likely to cause side effects. It is classified as a sugar alcohol, though, and in turn can have a laxative effect when consumed in large amounts. Thus, it may cause diarrhea, excessive urination and dehydration if you eat a lot of it. Glycerin suppositories are used to relieve constipation because of this effect.
Mucous Membrane Irritant
- R. Price in the book “Do You Have Kitchen Disease,” states that vegetable glycerin can cause irritation to mucous membranes.
- Shirley Price and Len Price state in the book, “Aromatherapy for Health Professionals,” vegetable glycerin irritates the mucous membranes of the genitourinary, respiratory and alimentary tracts, which may cause diarrhea, aches, irritation of the upper airway, wheezing, swelling of the tongue and gastroenteritis.
Many personal lubricants, like K-Y jelly, contain glycerin which breaks down to sugars and promotes yeast infections and possibly also bacterial vaginosis, noted Dr. Mary Marnach, a specialist in obstetrics and gynecology at the Mayo Clinic in Rochester, Minnesota. “For this reason I recommend lubricants without glycerin such as Astroglide Free and those that are silicone based (K-Y Intrigue) over the counter,” Marnach said.
“Women should be aware that there is mounting evidence that some products that are inserted vaginally can cause damage to vaginal tissues, and can increase the risk of bacterial vaginosis and sexually transmitted infections,” lead author Joelle Brown of the University of California, Los Angeles, told Reuters Health.
Other Side Effects
The more common, less serious side effects that can occur when you consume large amounts of vegetable glycerin include nausea, vomiting and headache. Lying down after taking medicinal amounts of vegetable glycerin can help limit the risk of headache and help relieve headaches that do occur, according to PubMed Health. When used as a medicine, glycerin must be prescribed by a doctor and used under medical supervision.
Allan B Wolfson and his co-authors, in the book “Harwood-Nuss’ Clinical Practice of Emergency Medicine, say “ingesting propylene glycol at high doses of the substance, can result in central nervous system disorders, renal failure and even fatalities in humans”.
Rare Side Effects
Some less common side effects that warrant immediate medical attention include confusion and irregular heartbeat. These would be extremely unlikely to occur with the small amounts typically used in foods, as they aren’t common even in medicinal doses.
Potential Allergic Reactions
Vegetable glycerin is made from either palm oil or coconut oil, so if you’re allergic to either of these oils, you should avoid vegetable glycerin. Otherwise, it could cause an allergic reaction, with symptoms including difficulty breathing, swelling, rash, itching and anaphylaxis. Use animal-based forms of glycerin, which are made from beef tallow or other animal fats, or synthetic glycerin, which is made from corn syrup, sugar cane or a petroleum derivative called propylene, instead.
FDA Notification to Industry
Products using oils, glycerin, or protein that were derived from the Jatropha plant may have toxic effects. The U.S. Food and Drug Administration (FDA) is notifying the regulated community that oils, glycerin, and proteins commonly used in the production of human and animal food, medical products, cosmetics, and other FDA-regulated products may contain toxins if they are derived from the Jatropha plant.
- Pei San Kong, Mohamed Kheireddine Aroua, Wan Mohd Ashri Wan Daud, “Conversion of crude and pure glycerol into derivatives: A feasibility evaluation”, Renewable and Sustainable Energy Reviews, 2016, Volume 63, pp. 533-555. doi:10.1016/j.rser.2016.05.054
- Sims, Bryan (25 October 2011). “Clearing the way for byproduct quality: why quality for glycerin is just as important for biodiesel”. Biodiesel Magazine.
- Yu, Bin (2014). “Glycerol”. Synlett. 25 (4): 601–602. doi:10.1055/s-0033-1340636.
- Stevens, Alan. “Preserving flowers and decorative foliages with glycerin and dye” (PDF).
- Nikolov, Ivan. “Functional Food Design Rules”.
- “Glycerin Enema”. Drugs.com. Retrieved 17 November 2012.
- “Glycerin (Oral Route)”. Mayo Foundation for Medical Education and Research.
- Long, Walter S. (14 January 1916 – 13 January 1917). “The composition of commercial fruit extracts”. Transactions of the Kansas Academy of Science. 28: 157–161. JSTOR 3624347. doi:10.2307/3624347.
- Does alcohol belong in herbal tinctures? newhope.com
- Lawrie, James W. (1928) Glycerol and the glycols – production, properties and analysis. The Chemical Catalog Company, Inc., New York, NY.
- Leffingwell, Georgia and Lesser, Miton (1945) Glycerin – its industrial and commercial applications. Chemical Publishing Co., Brooklyn, NY.
- The manufacture of glycerol – Vol. III (1956). The Technical Press, LTD., London, UK.
- Dasgupta, Amitava; Klein, Kimberly (2014). “4.2.5 Are Electronic Cigarettes Safe?”. Antioxidants in Food, Vitamins and Supplements: Prevention and Treatment of Disease. Academic Press. ISBN 9780124059177. Retrieved 16 August 2017.
- Hudgens, R. Douglas; Hercamp, Richard D.; Francis, Jaime; Nyman, Dan A.; Bartoli, Yolanda (2007). “An Evaluation of Glycerin (Glycerol) as a Heavy Duty Engine Antifreeze/Coolant Base”. SAE Technical Paper Series. SAE Technical Paper Series. 1. doi:10.4271/2007-01-4000.
- Proposed ASTM Engine Coolant Standards Focus on Glycerin. Astmnewsroom.org. Retrieved on 15 August 2012.