Propionic acid, or propanoic acid, is a colorless, corrosive, short-chain carboxylic acid with a pungent odor, soluble in water and various common organic solvents. It has numerous industrial applications due to its ability to be converted into a range of secondary compounds, leading to a wide variety of products.
Propionic acid is a naturally occurring organic acid produced through the fermentation process of bacteria from the Propionibacterium genus. It is found in various environments, including dairy products, the stomachs of ruminant animals, and even in human metabolism. For instance, Propionibacterium bacteria are involved in the maturation of Swiss cheese, converting lactic acid and lactates into propionic acid and carbon dioxide, the latter responsible for the characteristic holes in the cheese.
In cattle, these bacteria aid in digesting cellulose in their diet and release propionic acid and acetic acid in the rumen, which are used as energy sources after extensive metabolic pathways. In humans, the acid is produced in small amounts from amino acid breakdown and fatty acid oxidation in the intestines.
In industry, propionic acid is commonly used as a food and feed preservative and as a crucial chemical intermediate in the synthesis of cellulose fibers, herbicides, perfumes, cosmetics, colorants, artificial fruit flavors, esters used as solvents, plasticizers, rubber products, and pharmaceuticals. Below are some of the diverse industrial applications of Propionic Acid.
Food Grade Preservative
Propionic acid has various industrial applications. Initially, we will discuss its use in food preservation. According to the FAO and WHO (Food and Agriculture Organization of the United Nations; World Health Organization), propionic acid is permitted for food preservation (in bread, cakes, cheeses, meats, fruits, vegetables, and canned sausages) and beverages, at a maximum concentration of 3,000 mg/kg.
In Brazil, propionic acid is an approved preservative by the National Health Surveillance Agency (ANVISA). It is also listed in the U.S. Food and Drug Administration’s (FDA) Generally Recognized as Safe (GRAS) list, confirming that its addition to foods poses no health risks. It can be used as a preservative in the form of pure acid or its sodium, calcium, and potassium salts.
In Brazil, is there a limit for its use as a food preservative? ANVISA, the responsible public agency, publishes and updates resolutions for each food category. For example, concerning authorized food additives for meats and meat products, the most recent resolution, RDC Nº 272, of March 14, 2019, sets maximum limits and conditions of use at 0.5 g/100g for both Propionic Acid and sodium and potassium propionates.
Some foods, like certain cheese varieties, naturally contain propionic acid produced during maturation. However, the small amount produced is insufficient for food preservation, requiring additional solutions such as calcium and sodium propionates. According to the aforementioned RDC, when two or more food additives with the same technological function are used, and there are maximum numerical limits, the sum of these additives in the final product must not exceed the highest limit established for the additive allowed in the largest quantity. Therefore, it is advisable to check the legislation and stay informed about additive use for different food categories.
Feed Grade Preservative
For animal feed preservation, propionic acid or its derivatives, known as propionates, are widely used due to their effective long-term preservation. The choice of molecule depends on storage conditions. For example, in agriculture, ammonium propionate is commonly used due to its lower corrosiveness to agricultural equipment. Propionate solutions can be applied to high-moisture grains stored in silos, such as oats, corn, or sorghum. Other uses include preserving forages like hay and silage storage surfaces.
Its action primarily targets mold growth, which can produce mycotoxins leading to animal productivity issues such as gastric problems, fertility issues, and immune deficiencies, all of which are closely related to farm economics. It also combats yeast, bacteria, and insects like weevils, which, depending on infestation levels, can cause significant losses in stored products. Application methods include spraying on raw materials or feed and does not require a withdrawal period for animal products. Another common method is application via water, as the acid prevents algae and other microorganisms from contaminating the feed.
Other Industrial Applications of Propionic Acid
In the pharmaceutical industry, propionic acid is used as an antimicrobial in drug formulations. It is also a common ingredient in creams, lotions, and solutions to prevent microorganism contamination during drug handling or storage.
Another application is as a raw material for producing acrylic acid, used in manufacturing plastics, food packaging, adhesives, surfactants, paints, coatings, among other products. Carboxylation of propionic acid is a critical step in this process. Propionic acid also finds applications in other chemical industry branches, such as ester-based solvents production, herbicide manufacturing, and organic compound synthesis.
Its industrial synthesis occurs through two main routes: chemical from petrochemical feedstocks and fermentation, which is becoming an attractive alternative for producing this acid from renewable resources.
Industrially, propionic acid is obtained from petrochemical feedstocks with good production volumes. However, petroleum-based feedstocks are non-renewable, with volatile prices and limited availability in certain regions. Some production routes include Reppe, Oxo, and processes where propionic acid is a byproduct.
The Reppe process involves an exothermic reaction of ethylene with carbon monoxide and water in the presence of a nickel tetracarbonyl catalyst; the Oxo process (hydroformylation of olefins) involves ethene and synthesis gas forming propanal, followed by oxidation of the aldehyde; propionic acid obtained as a byproduct in acetic acid production via hydrocarbon oxidation.
A significant amount of propionic acid can be obtained by direct oxidation of hydrocarbons. This process is mainly used for acetic acid production, with propionic acid, formic acid, and a mixture of butyric acid isomers formed as byproducts. The proportion of propionic acid varies with the feedstock used.
Biotechnological production of propionic acid offers the advantage of using renewable raw materials and agro-industrial waste like sugarcane bagasse, molasses, and glycerol from biodiesel production. However, the produced volume is still economically uncompetitive with petrochemical production due to long fermentation times, low productivity, low final acid concentration, low yield, and the formation of byproducts that complicate and increase the cost of propionic acid recovery and purification.
Interested and want to know more? Contact our technical consultants for applied solutions!
Also read: Certified Grains – Sustainability and Safety.
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