It is used less than sodium benzoate in past years, but now it seems the market demand is increasing. Potassium benzoate is used as a substitute preservative for sodium benzoate primarily in acidic foods where the sodium content needed to be lower. The following food may contain with it:

soda
juice
cider
margarine
syrup
jelly
dressing
And let’s have a closer look at what soda manufacturers say about it.

Coca Cola: used as a preservative and to protect taste. (2)
Pepsico: in the carbonated soft drinks, such as in Diet Pepsi and Sierra Mist to preserve freshness. (3)
Properties
Solubility
In water: 73.83 g/100 mL (25 °C) in water, approximately 21 times that of benzoic acid, 3.44 g/L (25 °C). It dissociates into two distinct parts in water, the benzoate anion and potassium cation. The benzoate anion is the conjugate base of the benzoic acid.

In organic solvents: soluble in ethanol, slightly soluble in methanol, insoluble in ether.

PH
The pKa of benzoic acid is 4.2. The preservation function is better in low-pH products, below 4.5 or below its pKa.

Preservation Mechanism
The mechanism of action is the same with that of sodium benzoate, and also similar to sorbates, but different with the bio preservative – natamycin. Benzoic acid forms when potassium benzoate dissociates in water and combines with proton. The undissociated benzoic acid enters the microbial cell and inhibits cell growth. This is how it works and plays a role in food preservation.