Sorbic acid
- (2E, 4E)- hexa- 2 ,4- dienoic acid
- Hexadienoic
- E 200
White solid with a slightly acidic, scratchy taste
Fixed
1.2 g · cm -3 ( at 20 ° C)
134 ° C
228 ° C ( decomposition above 190 ° C)
1 Pa ( 20 ° C)
4.76 (20 ° C)
- Little in water: 1.6 g · l-1 (20 ° C)
- Better in hot water
- Very good in methanol, ethanol, dioxane, acetone
Attention
7360 mg · kg -1 ( LD50, rat, oral)
Template: Infobox chemical / molecular formula search available
Sorbic acid (also hexadienoic ) is a doubly unsaturated carboxylic acid. It is used both as free acid in force in the EU designation E 200 and in the form of their salts - used as a preservative and food additive - the sorbates.
Properties of the acid
Sorbic acid is only poorly, however, is well soluble in hot water in cold water. Very soluble sorbic acid is also in alcohols, concentrated acetic acid (glacial), acetone and toluene. It absorbs light at a maximum of 264 nm, the pKa is 4.76. The acid has a weak acid, " scratchy " taste, however, is not perceptible at the concentrations used for the preservation of food.
Synthesis
In the laboratory, the presentation of sorbic acid is carried out by a Knoevenagel condensation. To malonic acid is dissolved in pyridine, then reacted with crotonaldehyde, and piperidine. Another possibility is the reaction of ketene and 2- butenal, in an inert solvent and a catalyst ( for example, a zinc (II) salt). This gives a polymeric ester of 3-hydroxy -4- hexenoic acid, can be converted by heating or alkali treatment sorbic acid.
Natural Occurrence
In nature is a precursor of sorbic acid, the parasorbic acid contained in rowan berries. The rowan Sorbus aucuparia was also the namesake of the sorbic acid. The lactone is properly called 5,6- dihydro -6-methyl -2H -pyran- 2-one and is an oily liquid with a sweetish aromatic odor. From this, formerly known as Sorbinöl connection, free sorbic acid was shown first time in 1859. Finally, sorbic acid comes in wine and chemically bound in the fat of some aphid species ( aphids ) ago.
Use as a preservative
Sorbic acid is mainly required as a preservative for food and feed, pharmaceuticals, cosmetics and cleaning products. Is used sorbic acid itself ( E 200 ) or one of its better water-soluble salts. Of industrial importance are potassium sorbate (E 202) and calcium sorbate (E 203). Sodium sorbate ( E 201 ) is sensitive to oxidation and is not industrially produced. Sorbic acid is in contrast to benzoic acid imperceptible odor and taste.
With sorbic acid, for example, baked goods, margarine, cheese and sausages are preserved. The wholesomeness of sorbic acid has been demonstrated in various animal feeding studies. The allergenic potential is considered low, as it is utilized in the human body, such as a certificate from the diet fatty acid. However, it may act to trigger allergies in rare cases and irritate mucous membranes or skin as the acid of very sensitive individuals. The permitted daily dose of sorbic acid is 0-25 mg / kg body weight. It is approved in nearly all European countries as a food additive in the United States and has the so-called GRAS status ( Generally Recognized as Safe).
Another important application is the stabilization of wine against secondary fermentation by yeasts still present. In the production of wine, therefore, the addition of more than 0.2 g / l ( Germany and Austria) and 1 g / l ( U.S.) is allowed to the must or wine. Because the acid does not act against lactic acid bacteria and of these the sorbinol (E, E-2 ,4- hexadiene -1 -ol) is reduced, it can come of wine to undesirable and irreversible changes in taste ( Geranienton ). These result in the degradation of sorbic acid by lactic acid bacteria, which is why the wine is usually additionally stabilized with sulfur dioxide. See also: Wine Bug # Geranienton.
The tobacco regulation allows the use of sorbic acid as a preservative of tobacco products.
Effect of sorbic acid against microorganisms
The antimicrobial effect of the sorbic acid is based on various factors. Firstly, it is directed against various enzymes in the cells of microorganisms. Mainly the enzymes of carbohydrate metabolism of which are such as affect the enzyme Emulase. In addition, sorbic acid interferes with the citric acid cycle. There inhibits inter alia, the enzyme isocitrate dehydrogenase, and therefore the step of isocitric acid to Oxalbernsteinsäure and the enzyme α -ketoglutarate dehydrogenase, that is, the reaction of the α -ketoglutaric acid to succinic acid.
Further is sorbic acid and their double bonds, covalent bonds with SH groups of enzymes a, these are thereby inactivated. It is believed that the inhibitory effect of the sorbic acid back to the micro-organisms on the inhibition of several enzymes. Is still also assumed that the sorbic acid has effects on the cell wall. You inhibited namely at very low concentrations, the absorption of amino acids such as serine or alanine.
Thus, it can be effective at all in the microbial cell, it must penetrate the cell wall. Preferably, the undissociated acid fraction enters the cell. This is also the most important when it comes to the effectiveness of the substance. At a pH value of 3.15, 40% of sorbic acid present can enter the cell interior. This shows the dependence of the preservatives on pH.
In the presence of sorbic acid in low concentrations and simultaneously high bacterial counts, the microorganisms sorbic acids can include in their metabolism with. This means that sorbic acid is only to maintain impeccable hygienic food and not for recovery of germ-free conditions, as it is illegal anyway in the practice of food preservation.