Potassium Sorbate as Preservative

 

Potassium sorbate as preservative

Potassium sorbate is supplied in granular form that shows that it is not the preservative for liquid and semisolid dosage form because granules enhance the flow of dry powder while in liquid and semisolid dosage form, the preservative is dissolved in water or suitable solvent before its addition into product, so in that case there is no need to add additional step of granulation.

Potassium sorbate is used as preservative in sachet commonly and may also be used in dry suspension. It’s one advantage over sodium benzoate is that it is stable till pH 6 while sodium benzoate is stable till pH 5. And potassium sorbate is freely soluble in water as sachet powder requires free solubility because sachet is dissolved in water before use, so it is most suitable in sachet. It also produces very fresh feel in the mouth when taken as sachet solution because it is rapid in action and immediately kills microorganisms in mouth.

Mechanism of action:

Mechanism of action of potassium sorbate is that it is immediately converted to sorbic acid and achieves equilibrium with sorbic acid. Sorbic acid performs preservative function. Sorbic acid has two qualities. It is lipophilic & it is acid. So, it is absorbed into cell membrane of fungus. Fungus contains three types of phospholipids: Phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid. These three phospholipids are balanced in cell membrane and they have specific functions. Disturbance in their balance results in phosphate toxicity and phosphate starvation which disturbs growth and reproduction. Sorbic acid is absorbed and attacks at phospho groups and disturbs their balance and hence kills fungus. Its effect is much better on fungus than bacteria.

When Potassium sorbate is used with calcium containing products, after converting into sorbic acid it again reacts with calcium salts to form calcium sorbate and carbon dioxide is released in this reaction hence it also produces effervescence that improves patient compliance which gives the image that it is something powerful. Also, calcium sorbate has much better absorption than calcium carbonate due to its lipophilic nature. 

Potassium sorbate also has property to bind with many flavors because its structure is similar to many flavors, so it improves the intensity of flavor both on taste buds and smell receptors.

Potassium sorbate is not used as preservative in syrup and cream because it is straight chain lipophilic compound. As air is always absorbed in liquids, this air oxidizes sorbic acid. Hence sorbic acid is auto oxidized forming acetaldehyde and acrolein as its end products. Hence in syrup and cream, potassium sorbate shows no activity. But if certain antioxidant like propyl gallate is added then it itself transfers the proton to sorbic acid and prevents the loss of proton in sorbic acid and hence prevents oxidation. So, potassium sorbate is also effective in syrup and cream in presence of antioxidant.

Written by: Mudasir Abbas