Propylene glycol (abbreviation ‘PG’), a synthetic alcohol also known as 1,2-propanediol, its food grade is commonly used as a solvent carrier, humectant, thickener, emulsifier and stabilizer in food with the European food additive number E1520, while the industrial grade is used as a safer antifreeze substitute of ethylene glycol.
Commercial PG is mainly produced in the following three ways:
- Reacting propylene oxide (derived from petroleum) with water, with the following reaction equation:
- Reacting propylene with chlorinated water to form 1-chloro-2-propanol then hydrolyzed using sodium carbonate solution.
- Glycerin hydrogenolysis: reaction between glycerin (commonly vegetable derived) and hydrogen with a catalyst.
|Appearance||A colourless, hygroscopic and viscous liquid, odorless and tasteless|
|Solubility||Soluble in water, ethanol and acetone|
PG can be used in a wide range of applications, including food, animal feed, cosmetics and pharmaceuticals, as well as in antifreeze and coolant.
Propylene glycol is commonly used as a humectant by retaining moisture and a solvent carrier by dissolving other ingredients for further food processing. The following food products may contain it:
- Salad dressing
- Ice cream
- Puddings and desserts
- Sauces and Soups
- Sweet food
- Baking ingredients and mixes
Flavors & fragrances, vitamins and colors
Propylene glycol functions as a solvent and carrier in the preparation (dilution) of flavors & fragrances and vitamins to distribute them evenly throughout the end product, it also acts as an emulsifier to improve the stability of the emulsion.
PG is an ideal solvent to dissolve food colorings because of miscible with a broad range of solvents, not volatile and inexpensive.
Bread and pastry
Its emulsifying and moisturizing properties have been widely utilized in the manufacture of bread and pastry. It reduces the production time of bread and prolongs the shelf life by preventing the aging of bread and pastries through maintaining moisture.
Propylene glycol alginate and Propylene glycol esters of fatty acids
As a raw material to produce propylene glycol alginate (PGA) and propylene glycol esters of fatty acids (PG ester). PGA is used as a thickener and PG ester as an emulsifier in food.
A humectant to attract and hold water to keep the animal feed moist and fresh. Meanwhile, it enables the feed uses in zero temperature by reducing the freezing point of water.
It can be used as a humectant, skin conditioning, solvent and viscosity controlling (1) in cosmetics and personal care products.
The following products may contain it:
- Hair products
One of the most common purposes to add propylene glycol in wipes is as a humectant, a similar function with glycerin. The skin can maintain moisture for a short time after wiping as PG can absorb some moisture from the air to the skin to avoid dry skin caused by liquid evaporation after wiping.
Another reason for adding it is its antibacterial property. Wipes are disposable, but many of them are not packaged in a single piece, and the unused ones are easy to contact with the air and contaminated with bacteria after being opened.
The antibacterial activity of propylene glycol can delay or inhibit the growth of bacteria on wipes, thus protecting the safety of users. This property is especially important when wipes are for women and baby.
PG is an important industrial raw material and intermediate for the production of unsaturated polyester resin, epoxy resin, and polyurethane resin. It is also widely used as an antifreeze and coolant.
Antifreeze & Coolant
Antifreeze is a liquid typically a mixture of distilled water and ethylene glycol or propylene glycol. It has a low freezing point to make sure the engine does not freeze at a low temperature. Antifreeze also refers to the pure chemical, for example, ethylene glycol or propylene glycol.
With a low freezing point of -59°C, industrial grade propylene glycol can be used as an antifreeze by lowering the water freezing point, and also as a coolant by raising the boiling temperature of the water and taking away a lot of heat generated during the operation of the engine for its high boiling point of 188.2 °C.
With the advantages of anti-boiling, anti-corrosion, and anti-freezing, PG can be used for cooling systems such as automobiles and ships.
Propylene glycol (PG) vs ethylene glycol (EG)?
Both are glycol with two hydroxyl groups (-OH) in the molecule structure but totally different. The difference between them mainly in four points:
- Toxicity: ethylene glycol is the earlier used and the most common antifreeze, but due to its higher toxicity and not easily biodegradable, it is dangerous to humans and pets. Propylene glycol is an alternative to it.
- Uses: food grade propylene glycol can be used as a food additive, whereas the latter cannot.
- Performance: EG has better efficiency in freeze point depression than PG due to its lower viscosity.
- Price: PG is more expensive than EG.
Yes, it almost has no side effects and the safety has been approved by the U.S. Food and Drug Administration (FDA) and European Food Safety Authority (EFSA), as well as the Joint FAO/WHO Expert Committee on Food Additives (JECFA).
Some consumers are concerned when they see propylene glycol in the ingredients list of their food, and question how we can eat the food with the ingredient made of antifreeze which is harmful to humans.
Propylene glycol is a multi-functional ingredient generally recognized as safe (GRAS) that can be used as an anticaking agent, dough strengthener, emulsifier, humectant, solvent, stabilizer, thickener, texturizer and others in food. The following are the approved food uses with the maximum levels (2):
- Seasonings and flavorings 97%
- Confections and frostings 24%
- Nuts and nut products 5%
- Frozen dairy products 2.5%
- Others 2.0%
Propylene glycol (E1520) is an authorised food additive in the European Union (EU) that can be used as a carrier in “colours, emulsifiers and antioxidants”, enzymes, all flavourings and all nutrients. (3)
Safety re-evaluation in 2018
After the studies of metabolism, genotoxicity, chronic & subchronic toxicity, reproductive & developmental toxicity, and other researches, EFSA concluded there was no reason to revise the current ADI of 25 mg/kg bw per day, which was established in 1996.
EFSA did not consider propylene glycol as an allergen as a food additive. Also, although with low irritant potency, no allergy potential or immunotoxicity of propylene glycol has been reported when used in cosmetics until 2011 by Cosmetic Ingredient Review (CIR). (4)
Function Class: food additives, carrier solvent, glazing agent, humectant. (5)
Acceptable daily intake: ADI “0-25 mg/kg bw” set in 1973. (6)
What’re the substitutes of propylene glycol?
It depends on the specific uses. In some food, the alternatives can be sorbitol and glycerol, as both can be used as humectants.
Is it vegan?
Yes, propylene glycol made from the above three manufacturing processes are all vegan as without using animal-derived products, so it is suitable to the diet of vegetarians.
Is it gluten free?
Yes, propylene glycol is gluten free as without wheat, rye, barley, or crossbreeds of these grains.
Now you may have a knowledge of the humectant & solvent carrier – Propylene Glycol (E1520), from the following aspects:
- Three manufacturing processes.
- Uses in food, animal pets, cosmetics and antifreeze & coolant.
What kinds of food labels have you found this ingredient in? Or if you have any questions or remarks about this additive, feel free to let me know in the comments.