Why is that in my Food? : Propylene Glycol

I've been meaning to start a series on food additives and why they're in foods. Often, food ingredients list a lot of words that people don't understand and.or know their purpose/safety - despite what one might hear, not being able to pronounce a word on a food label is not a reason to not consume that food. Words on the food label like Pantothenic Acid and Pyridoxine might sound frightening, but they're actually just vitamins B5 and B6. There's unfortunately much fearmongering that surrounds food additives that often strays far from science or even precautionary principles, so I figured i'd do a little mini-series on the topic.

What better way to segue into this  than with the recent talk of propylene glycol in Fireball, a popular cinnamon flavored whiskey.The story was reported on here. Fireball was recalled in Europe, after an American shipment was sent overseas. The amount of propylene glycol allowed in American Fireball is different than Europe, so it was recalled. Fireball has released an official statement on the matter here.

mpbio.com

For starters, people have been fearmongering with this issue, noting that propylene glycol is used as anti-freeze as well.  Anti-freeze is a very general term; there is not one 'anti-freeze'. Anti-freeze refers to a chemical that reduces the freezing point - addition of anti-freezes to water can drop its freezing point from 0 degrees Celsius to the negatives. The major reason that individuals associate anti-freeze with death is because a common anti-freeze was ethylene glycol, a  bright yellow/green liquid with a sweet smell that is highly toxic to mammals (1). The use of ethylene glycol is often replaced by propylene glycol, largely due to the fact that it is still an effective anti-freeze but significantly less toxic to humans (2).  Something as simple as glycerol, a component of the triglycerides in your body, can be used as an anti-freeze. Anyone who has compared propylene glycol to anti freeze to inspire fear has done nothing but demonstrate a lack of chemistry knowledge. If I've said it once, I've said it a thousand times: be extremely skeptical of anything you hear about food or nutrition from the media.

So what is propylene Glycol? It's a liquid, colorless, odorless solvent that can hold onto water (3).

What is its role in food? It is used to maintain moisture (a humectant) and as a solvent for food colors and flavors.

Is it toxic? Yes, virtually everything is toxic at a specific dose.

What dose is toxic? The toxicity data for propylene glycol can be split into inhalation, dermal (skin) and oral routes. Since we're talking food, we'll go with the oral toxicity. The LD50 in rats is 20,000mg/kg. Chronic exposure studies in rats, both male and female, at doses varying from 0 to 50,000ppm (2.5g/kg/d), for 2 years, showed no toxic effects on any organ system, blood, and no increase in mortality. The highest levels (and no level for that matter) did not show an increased incidence of neoplasms (cancer) and were not teratogenic (reproductive toxicity). The level causing no toxicological effect has been set at 2500mg/kg. Single oral doses of 1.5g/kg cause dizziness in human adults. (2,4). The WHO sets an acceptable daily intake at 0-25mg/kg (5) - giving the common 100x fold reduction as a margin of safety.

How is Propylene Glycol metabolized?  Propylene glycol is absorbed in the bloodstream from the gastrointestinal tract. It has a half life of 4 hours. It is metabolized by alcohol dehydrogenase in the liver to lactic acid and pyruvic acid (two normal biological metabolites) (6). Lactic acid production is the common pathway. Other metabolites include acetic acid and propionaldehyde. The kidneys filter almost half of the absorbed propylene glycol unaltered or as a glucuronide conjugate (a normal process in xenobiotic metabolism).

What does the FDA think of Propylene Glycol? The FDA has given propylene glycol the status of "Generally Recognized as Safe" (7). Many are skeptical of GRAS designations, but note that propylene glycol received a conclusion 1 label, meaning:

There is no evidence in the available information on [substance] that demonstrates, or suggests reasonable grounds to suspect, a hazard to the public when they are used at levels that are now current or might reasonably be expected in the future.

-For more on the levels of GRAS determination, see here.

European vs American standards? Dow has a nice side by side comparison of the European and American standards here. The standards are very similar. Neither would be bring you to any level even close to oral toxicity. It appears the major difference between US and European standards relate to concern over young children's ability to metabolize propylene glycol, especially those with pre-existing liver and kidney conditions - see here. Hopefully, young children won't be consuming too much Fireball...

So...that's why propylene glycol is in your food! If you're concerned about Fireball toxicity, be concerned with the ethanol, not the propylene glycol!


1. http://www.epa.gov/kidshometour/products/coolant.htm
2. http://www.umich.edu/~nppcpub/resources/compendia/CHEMpdfs/CHEMV.pdf
3. http://www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=240
4. http://www.inchem.org/documents/jecfa/jecmono/v05je90.htm
5. http://apps.who.int/food-additives-contaminants-jecfa-database/chemical.aspx?chemID=2698
6. http://www.atsdr.cdc.gov/csem/csem.asp?csem=12&po=14
7. http://www.fda.gov/food/ingredientspackaginglabeling/gras/scogs/ucm261045.htm