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CAS Number: 79-09-4
Synonyms: Propanoic acid, E280, ethanecarboxylic acid, methylacetic acid, carboxyethane, pseudoacetic acid, propionic acid (natural; also produced synthetically)
Physical Properties: Clear, colorless oily liquid with a pungent, slightly rancid, acidic odor (reminiscent of Swiss cheese or sweaty socks). Miscible with water (approx. 37 g/100 mL at 20°C, forming homogeneous solutions). Miscible with ethanol, diethyl ether, chloroform, and most organic solvents. Molecular weight 74.08 g/mol. Melting point -21.5°C. Boiling point 141°C. Density 0.993 g/cm³ at 20°C. Vapor pressure 3.3 mmHg at 20°C (volatile; noticeable odor even at low ppm levels). pKa 4.88 (weak organic acid). Log P (octanol-water) 0.33 (moderately hydrophilic). Flash point 54°C (combustible liquid). Can form propionic anhydride under heating.
Applications: Bakery products (bread, especially rye bread, sourdough, pita, tortillas; cakes, pastries, muffins, and other baked goods) as a mold inhibitor to prevent rope spoilage by Bacillus subtilis and B. mesentericus and growth of Penicillium, Aspergillus, and Fusarium. Animal feed preservative for stored grains (barley, corn, soybeans, wheat), hay, silage, and compound feeds (prevents heating, molds, and bacterial spoilage; inhibits Salmonella). Cheese (as a natural component up to 1 percent in Swiss cheese, but added only as part of starter cultures, not as direct additive). Fruit and vegetables (as a dip or spray for apples, citrus, and potatoes to control post-harvest rot). Industrial production of propionate salts (calcium, sodium, potassium – E281, E282, E283); cellulose propionate plastic; herbicide intermediates; perfume and flavoring agents (artificial fruit flavors, rum flavor). Pharmaceuticals (preservative in topical creams and ointments). Cosmetics (preservative in lotions and shampoos with lower irritation than parabens).
Description:
Propionic acid (E280) is a naturally occurring short-chain fatty acid with three carbon atoms (C3) that serves as a potent mold inhibitor and antibacterial agent, primarily used in bakery products to prevent spoilage. Its chemical structure is CH₃CH₂COOH. In nature, propionic acid is produced by Propionibacterium freudenreichii and related bacteria during the fermentation of carbohydrates, such as in Swiss cheese, where propionic acid contributes to the nutty, sweet flavor characteristic of Emmental cheese. The compound is produced industrially by two main methods: hydrocarboxylation of ethylene (the Reppe process: C₂H₄ + CO + H₂O → CH₃CH₂COOH) using a nickel carbonyl catalyst, and oxidation of propionaldehyde derived from propylene. Global production is approximately 400,000 tons per year.
The mechanism of antimicrobial action is typical of weak organic acids. In the undissociated form, which is the protonated form present at pH below the pKa of 4.88, propionic acid diffuses across the microbial cell membrane. Once inside the higher-pH cytoplasm, where the pH is approximately 7.2, the acid dissociates into propionate anion and H⁺. The accumulated acid anions disrupt metabolic pathways while the released H⁺ acidifies the cytoplasm, forcing the cell to expend ATP to pump out protons via H⁺-ATPase pumps. Eventually, the microbe cannot maintain pH homeostasis, and metabolism ceases. Propionic acid is particularly effective against molds including Penicillium, Aspergillus, Fusarium, and Mucor, and against rope-forming Bacillus subtilis, which causes sticky, stringy spoilage in bread. However, it is less effective against yeasts than sorbic acid (E200) and less effective against bacteria than acetic acid (E260) or benzoic acid (E210). For this reason, propionic acid is optimal for bread at pH 5 to 6, where mold spoilage is the primary issue.
At typical usage levels of 1000 to 3000 parts per million in bread, propionic acid does not affect yeast fermentation by Saccharomyces cerevisiae because baker's yeast has a higher tolerance to propionate compared to molds. The acceptable daily intake for propionic acid and its salts established by JECFA in 1973 is "not specified," meaning it poses no safety concern at current usage levels. Propionic acid is rapidly metabolized in the human body via the propionyl-CoA pathway, where it is converted to succinyl-CoA and enters the Krebs cycle. There is no accumulation, and no carcinogenicity or reproductive toxicity has been observed.
The distinctive pungent odor of propionic acid, which is reminiscent of Swiss cheese, limits its use in bland foods. In bread, the concentration of 1000 to 3000 parts per million is low enough that the odor is not detectable after baking, but some consumers may notice a slight sharp aftertaste. In animal feed, propionic acid is often applied to grain at harvest to inhibit mold growth and mycotoxin production, including aflatoxins, ochratoxins, and fumonisins. For example, high-moisture corn with over 20 percent water content is treated with 0.5 to 1 percent propionic acid to allow safe storage for up to 12 months without drying, saving significant energy. In silage, which is fermented forage for cattle, propionic acid reduces heating and spoilage while increasing aerobic stability. However, calcium propionate (E282) is more common in bakery because the calcium salt is a powder (solid) and easier to handle. The liquid form of propionic acid (E280) is used in industrial bakeries with automated micro-dosing systems, where the liquid can be sprayed directly onto dough. One limitation is that aluminum equipment cannot be used due to corrosion; stainless steel or plastic is required. In the European Union, propionic acid is authorized as a preservative for bread and bakery products at quantum satis, up to 2000 milligrams per kilogram. In the United States, it is Generally Recognized as Safe (GRAS) for similar uses. Due to consumer demand for "preservative-free" bread, some artisanal bakers rely on lactic acid bacteria fermentation (sourdough) to produce propionic acid in situ instead of adding the pure compound. However, sourdough alone may not provide sufficient mold inhibition for a long shelf life of 7 to 14 days, so E280 remains widely used in packaged industrial breads. Compared to calcium propionate (E282), propionic acid has the advantage of not adding calcium ions, which might affect dough rheology in some recipes. Overall, propionic acid and its salts are considered among the safest and most natural preservatives because they occur endogenously in many foods and are normal human metabolites.
SAFETY INFORMATION ABOUT E280 – PROPIONIC ACID
First aid measures:
Description of first aid measures:
General advice:
Consult a physician.
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
If inhaled:
If breathed in, move person into fresh air.
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off contaminated clothing and shoes immediately.
Wash off with soap and plenty of water.
Consult a physician.
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
If swallowed:
Do NOT induce vomiting.
Never give anything by mouth to an unconscious person.
Rinse mouth with water.
Consult a physician.
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment.
Avoid breathing vapours, mist or gas.
Evacuate personnel to safe areas.
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste.
Keep in suitable, closed containers for disposal.
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place.
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles.
Faceshield (8-inch minimum).
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
Skin protection:
Handle with gloves.
Gloves must be inspected prior to use.
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product.
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices.
Wash and dry hands.
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls.
If the respirator is the sole means of protection, use a full-face supplied air respirator.
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions.
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company.
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product
