Brief Overview

Sorbic acid, or 2,4-hexadienoic acid, is a natural organic compound used as a food preservative. It has the chemical formula C₆H₈O₂. It is a colourless solid that is slightly soluble in water and sublimes readily. It was first isolated from the unripe berries of the rowan tree (Sorbus aucuparia), hence its name.  

Manufacturing Process

The traditional route to sorbic acid involves condensation of malonic acid and trans-butenal. It can also be prepared from isomeric hexadienoic acids, which are available via a nickel-catalyzed reaction of allyl chloride, acetylene, and carbon monoxide. The route used commercially, however, is from crotonaldehyde and ketene.

Food Industry

Sorbic acid is antimicrobial agent often used as preservative in food and drinks to prevent the growth of mold, yeast, and fungi. In general the salts are preferred over the acid form because they are more soluble in water, but it is the acid form that is active. The optimal pH for the antimicrobial activity is below pH 6.5. Sorbates are generally used at concentrations of 0.025 % to 0.10 %. Adding sorbate salts to food will, however, raise the pH of the food slightly so the pH may need to be adjusted to assure safety. It is found in many other foods, such as cheeses and breads.  Other Applications Sorbic acid can also be used as an additive for cold rubber, and as an intermediate in the manufacture of some plasticizers and lubricants.