Definition
Sodium propionate, also known as sodium propanoate, is the sodium salt of propionic acid with the chemical formula C₃H₅NaO₂ (or NaC₂H₅COO). It appears as a white, crystalline solid that is soluble in water.
Overview
Sodium propionate is employed primarily as a preservative in food products, where it inhibits the growth of molds and certain bacteria. It is designated as food additive E‑281 in the European Union. In addition to its role in the food industry, sodium propionate is used in animal feed, cosmetics, and as a buffering agent in various industrial processes. Its antimicrobial efficacy is most pronounced at acidic pH values, which enhances the conversion of the salt to its undissociated acid form, propionic acid, that penetrates microbial cell membranes.
Etymology/Origin
The name derives from its parent acid, propionic acid, itself named for its three‑carbon chain (“prop‑” from the Greek prop meaning “first” or “primary”, historically used for three‑carbon compounds) and the suffix “‑onic” indicating a carboxylic acid. The prefix “sodium” denotes the presence of the Na⁺ cation forming the salt.
Characteristics
| Property | Description |
|---|---|
| Chemical formula | C₃H₅NaO₂ |
| Molar mass | 96.07 g·mol⁻¹ |
| Physical state | White crystalline powder or granules |
| Solubility | Highly soluble in water (≈ 150 g L⁻¹ at 20 °C); poorly soluble in organic solvents such as ethanol |
| Melting point | 260 °C (decomposes) |
| pKa of parent acid | 4.87 (propionic acid) |
| Regulatory status | Approved as a food additive (E‑281) in many jurisdictions; acceptable daily intake (ADI) established by FAO/WHO Joint Expert Committee on Food Additives (JECFA) |
| Antimicrobial action | Inhibits spoilage organisms, especially molds (e.g., Penicillium, Aspergillus) and certain bacteria (e.g., Staphylococcus aureus). Activity is pH‑dependent, being strongest below pH 5.5. |
| Safety profile | Generally recognized as safe (GRAS) when used within prescribed limits. High oral doses may cause gastrointestinal irritation. |
Related Topics
- Propionic acid – the parent carboxylic acid from which sodium propionate is derived.
- Food preservatives – substances added to food to prevent microbial growth and extend shelf life; other examples include sodium benzoate (E‑211) and calcium propionate (E‑282).
- E‑numbers – European Union codes for substances permitted as food additives; sodium propionate is identified as E‑281.
- GRAS (Generally Recognized As Safe) – a U.S. FDA designation for substances considered safe for their intended use based on scientific consensus.
- Antimicrobial mechanisms of weak acids – the principle by which undissociated weak acids penetrate microbial membranes, leading to intracellular acidification and metabolic disruption.
References – Data compiled from standard chemical handbooks, regulatory agency publications (e.g., EFSA, FDA, JECFA), and peer‑reviewed literature on food preservation.