Among the three major preservatives benzoic acid, sorbic acid and propionic acid widely used in China, propionic acid is the most affordable, safe and effective edible preservative recognized worldwide, and the common propionate salts are calcium propionate and sodium propionate.

Characteristics of Propionic Acid and Propionate

Propionic acid: it is a three-carbon carboxylic acid. Pure propionic acid is a colorless or slightly yellow oily liquid with a slight irritating odor, relative molecular mass of 74.08, melting point of -22℃, boiling point of 140.7℃, relative density of 0.99, soluble in water, ethanol, ether and so on. High concentration of contact will cause local damage to the skin, eye mucous membrane surface.

Sodium propionate: It is white crystal, granule or crystalline powder, odorless or with slight acetic acid-butyric acid odor. Stable to light and heat, melting point above 400℃, deliquescent in wet air.

Easily soluble in water (100g at 15℃, 150g at 100℃), soluble in ethanol (4.4g at 15℃, 8.4g at 100℃), slightly soluble in acetone (0.05g at 15℃), obtained by the reaction of propionic acid and sodium carbonate.

10% aqueous solution of sodium propionate PH value of 8.49, in 10% aqueous solution of sodium propionate add the same amount of dilute sulfuric acid, heating is produced with propionic acid odor gas.

Calcium propionate: It is the calcium salt of propionic acid. White crystal, granule or crystalline powder, odorless or with a slight propionic acid flavor. Stable to light and heat, hygroscopicity, solubility in 100g of water: 20 ℃, 39.85g; 50 ℃, 38.25g; 100 ℃, 48.44g.

Slightly soluble in ethanol and methanol, almost insoluble in acetone and benzene. Calcium propionate can be synthesized directly from calcium oxide. Add the same amount of dilute sulfuric acid in 10% aqueous solution of calcium propionate, and the odor gas with propionic acid is produced after heating. Calcium propionate is alkaline, its 10% aqueous solution PH value is 8-10.

Anti-corrosion properties

The active ingredient of propionic acid and its salts is propionic acid, which must be in an acidic environment to produce antibacterial effect. It is the smallest when the PH value is 5.0, and the concentration of bacterial inhibition is 0.01%, and 0.5% when the PH value is 6.5. In the acidic medium of various types of molds, good itching bacillus or gram-negative bacilli have strong inhibitory effect on preventing the production of aflatoxin has a special effect, but almost ineffective for yeast.

Its antiseptic principle is:

(1) The monomer propionic acid molecule can form high osmotic pressure outside the mold cell, so that the mold cell is dehydrated and loses its reproductive force.

2) The active molecules of propionic acid can penetrate the cell wall of molds and other molds, inhibit the enzyme activity inside the cell, hinder the microorganisms from synthesizing β-alanine, and then organize the reproduction of molds.

Safety

Propionic acid is the intermediate product of normal metabolism of human body, which can be metabolized and utilized, safe and non-toxic. When propionic acid enters the human body or animal body, it can be converted into propionyl coenzyme A, D-methylmalonic acid monoacyl coenzyme A, L-methylmalonic acid monoacyl coenzyme A and succinyl coenzyme A in sequence.

Succinyl coenzyme A can enter both the tricarboxylic acid cycle for complete oxidative catabolism and the gluconeogenesis pathway for the synthesis of glucose and glycogen.

Among the metabolic pathways in animals, bacteria in the rumen of certain ruminants (e.g., cattle) are able to ferment sugars (e.g., cellulose) into propionic acid, which enters into lipid metabolism and gluconeogenesis via the pathways described above, and therefore does not cause damage to ruminant health.

The ADI for sodium propionate is not restricted (FAO/WHO) and the oral LD50 for mice is 5.1 g/kg body weight. Calcium propionate ADI is not restrictive (FAO/WHO) and the oral LD50 in mice is 3340 mg/kg body weight.

Propionate is not affected by other ingredients in the food and has the advantages of low corrosiveness, low irritation and suitable for long-term storage. In addition, since propionate does not have a fumigation effect, the mixing uniformity of foodstuffs is required to be high.

Application of propionic acid and propionate salt

According to “GB 2760 National Standard for Food Safety Standard for the Use of Food Additives”, propionic acid and its sodium salt, calcium salt as a preservative and its scope of use and the maximum amount of use (in propionic acid, g/kg) for: soybean products, bread, pastries, vinegar, soy sauce 2.5, raw and wet noodle products (noodles, dumplings, chaotic skins, siu mai skins) 0.25, the original grain 1.8. 3% -5% propionic acid is generally used to soak prunes in sodium solution. A 3%-5% sodium propionate solution is generally used to soak prunes, which need to be washed after soaking before they can be used to process canned prunes.

As a food preservative propionate, calcium propionate inhibits molds at a smaller effective dose than sodium propionate. The advantage of calcium propionate is that its use in pastries and breads supplements the calcium in the food.

Calcium propionate is mainly used in bread, because sodium propionate raises the pH value of bread and delays the fermentation of raw pasta; sodium propionate is mostly used in pastries because synthetic bulking agents are used for fluffing of pastries, and calcium propionate reduces the effect of chemical bulking agents.

Adding 0.188% of calcium propionate to dough with a pH value of 5.8 or 0.156% to dough with a pH value of 5.6 prevents the occurrence of “sticky filament disease” (caused by Bacillus subtilis) and avoids affecting the normal fermentation of yeast. Adding 0.25% calcium propionate to bread can prolong 2-4d without mold growth. Adding 0.15% calcium propionate to soy sauce can preserve it for 90d without mold.