What Plant Does Propionic Acid Come From? The Surprising Microbial Truth

November 26, 2025 •

2 min read

While many assume propionic acid comes directly from a plant source, the reality is far more complex and involves a microbial process. This naturally occurring compound, often used as a preservative, is primarily a byproduct of bacterial fermentation that utilizes plant-derived materials and other organic matter. Therefore, the answer to what plant does propionic acid come from is not a single plant, but rather a complex ecosystem of microbes that feed on plant sugars and fibers.

Quick Summary

Propionic acid originates primarily from bacterial fermentation of plant-derived sugars and organic substrates, not from the plants themselves. Specialized microorganisms, particularly from the genus Propionibacterium, are responsible for this conversion.

Key Points

Microbial Fermentation: Propionic acid is not made directly by plants but is a byproduct of anaerobic fermentation carried out by bacteria, especially Propionibacterium.
Plant-Derived Substrates: The bacteria responsible for production ferment various plant-based materials and agricultural waste, such as sugars from apple pomace, whey (from livestock fed plants), grains, and molasses.
Cheesemaking Agent: In Swiss-type cheeses, propionic acid bacteria ferment lactate to create the characteristic nutty flavor and the carbon dioxide that forms the 'eyes' or holes.
Gut Health Metabolite: Certain gut bacteria ferment dietary fiber to produce propionic acid as a short-chain fatty acid, which plays a vital role in gut and overall metabolic health.
Distinction from Indole-3-Propionic Acid: It's crucial to differentiate standard propionic acid from indole-3-propionic acid (IPA), a separate compound with auxin-like properties produced by microbes that interacts with plants.
Industrial vs. Biological Production: While some propionic acid is made naturally, most large-scale industrial production relies on petrochemical synthesis, though bio-based methods are gaining interest for sustainability.

The Microbial Origin of Propionic Acid

The notion that propionic acid is sourced directly from a specific plant is a widespread misunderstanding. The compound, also known as propanoic acid ($CH_3CH_2COOH$), is a short-chain fatty acid (SCFA) produced primarily through anaerobic fermentation of sugars and lactate by specific bacteria. This fermentation occurs in environments like the digestive tract of animals or during the manufacturing of certain fermented foods. Plants provide the raw materials, while microorganisms, especially Propionibacterium, are the producers.

Fermentation: The Crucial Biological Process

Biological production of propionic acid is a classic example of fermentation, a metabolic process releasing energy from molecules like glucose without oxygen. Bacteria such as Propionibacterium freudenreichii and Acidipropionibacterium acidipropionici are key players, utilizing the Wood-Werkman cycle to convert pyruvate into propionate, acetic acid, and carbon dioxide. This activity contributes to flavors in fermented foods.

Plant-Derived Feedstocks for Microbial Fermentation

Various plant-based materials and agricultural byproducts serve as substrates for propionic acid-producing bacteria:

Apple Pomace: A residue from juice production, rich in fermentable sugars used by Propionibacterium freudenreichii.
Whey Lactose: From dairy (cows consuming plants), lactose is a carbon source for propionic acid bacteria in cheesemaking.
Grains and Silage: Grains (corn, oats, wheat) are preserved with propionic acid, which is also naturally produced by microbes fermenting silage.
Molasses: Sugarcane and soy molasses provide inexpensive sugars for propionibacteria.
Lignocellulosic Biomass: Complex plant material potentially usable after pre-treatment and hydrolysis.

A Tale of Two Productions: Biological vs. Chemical Synthesis

Propionic acid is produced both biologically through fermentation and synthetically from petrochemicals. Biological production is important for food applications like cheesemaking, while chemical methods dominate industrial scale due to higher efficiency.


Feature	Biological Fermentation	Chemical Synthesis
Source Material	Renewable biomass	Petrochemicals
Producer Organism	Primarily Propionibacterium	None
Efficiency & Cost	Lower rate, expensive purification	Higher rate, scalable, easier purification
Environmental Impact	Sustainable, uses waste	Relies on fossil fuels
Byproducts	Acetic acid, CO2	Can have waste byproducts
Applications	Swiss cheese	Plastics, herbicides, preservatives

The Role in Cheesemaking and Gut Health

Propionic acid is key in Swiss cheeses like Emmental, where Propionibacterium ferment lactate, creating nutty flavor and CO2 (the 'eyes'). In the human gut, Bacteroides and Prevotella produce SCFAs, including propionic acid, from dietary fiber, supporting gut lining health and influencing metabolism.

The Special Case of Indole-3-Propionic Acid

Indole-3-propionic acid (IPA) is different from propionic acid. Produced by specific bacteria from tryptophan, IPA is an auxin-like molecule affecting plant growth. It links microbes and plants but isn't the preservative-grade propionic acid.

Conclusion

Propionic acid does not come directly from plants but is a result of microbial fermentation of plant-derived materials by bacteria, mainly Propionibacterium. This process is vital for certain foods and feed preservation. While chemical synthesis is common industrially, the biological route highlights the microbial conversion of plant matter.

For more information on bacterial producers and substrates, consult the review in MDPI.

Frequently Asked Questions

The primary group of bacteria that produce propionic acid are from the genus Propionibacterium, which includes species like Propionibacterium freudenreichii and Acidipropionibacterium acidipropionici.

In Swiss-type cheeses, Propionibacterium ferment the lactate produced by other bacteria. This process yields propionic acid, which creates the nutty flavor, and carbon dioxide, which forms the holes, or 'eyes'.

No, propionic acid is not typically found in significant amounts in fresh plants. It is a product of microbial activity that occurs after plants are harvested or processed, such as during fermentation.

In the human gut, propionic acid is a short-chain fatty acid (SCFA) produced by beneficial gut bacteria that ferment dietary fiber. It is important for colon health and influences metabolism.

No, not all plant-derived products are suitable. The best feedstocks are those rich in sugars, starch, or lactate, such as apple pomace, grains, and whey. Lignocellulosic materials require pre-treatment to release fermentable sugars.

Yes, propionic acid is often used as a preservative for high-moisture grains like corn and oats to prevent mold growth during storage.

Yes, when used as a food additive, propionic acid and its salts are generally recognized as safe (GRAS) by regulatory bodies. It is a natural metabolite and is safely digested by humans.