Potassium Sorbate: How it works, when it doesn’t work, and how much is too much

If you’re not familiar with the chemical potassium sorbate, then you are probably someone who doesn’t often read product labels. Potassium sorbate is used in tons of products as a preservative – from foods, to cosmetics, to pharmaceuticals. It has GRAS (Generally Recognized as Safe) status and is widely regarded as a safe, all-purpose antimicrobial and anti-fungal agent. Next time you’re snacking on some dried fruit, check the label for potassium sorbate – it might also be listed as E – 202. (It is almost never referred to by its IUPAC name, 2,4-hexa-2,4-dienoate.)

In this article, we’ll check out the chemistry of potassium sorbate, the stability, and some current uses. We’ll be sure to answer critical questions like: what makes potassium sorbate such a useful preservative? When does it work, and when does it become ineffective? Is potassium sorbate safe for human consumption? Finally, what are some innovations that take advantage of the properties of potassium sorbate?

Chemistry of Potassium Sorbate

To help us understand why potassium sorbate is so ubiquitous, let’s take a look at the chemistry. The sorbate ion from potassium sorbate as a deprotonated carboxyl group which is largely responsible for the antibacterial activity. Another important note about the structure of this molecule is its relatively short carbon chain. Molecules such as potassium sorbate and sodium acetate tend to be more powerful antimicrobial agents compared to their longer-chain analogues.

The effectiveness of potassium sorbate as an antimicrobial agent is also dependent on the matrix pH, which dictates to what extent the sorbate ion will be protonated. Potassium sorbate is most effective in acidic matrices, and is not recommended for alkaline products.

The role of potassium sorbate as a preservative

Potassium sorbate has demonstrable effectiveness against growth of many molds, yeasts, and bacteria. In general, it is thought to be more effective against molds and yeasts compared to bacterial growth. In particular, lactic acid bacteria is resistant to potassium sorbate and may even metabolize it.

The antimicrobial mechanism of potassium sorbate is not clearly defined. It is thought to bind to cell membranes where it can impair the activity of critical transport proteins.

Stability of Potassium Sorbate

Potassium sorbate breaks down into its potassium and sorbate ions, and may also form sorbic acid and sorbitol. In fact, it is commonly produced by reacting sorbic acid with potassium hydroxide. As mentioned above, the equilibrium concentrations of the dissociated ions and acid are dependent upon the pH, which is why potassium sorbate loses efficacy at a pH above 7.

Despite its high potency as a preservative, it is not entirely stable. Models in aqueous matrices show that more than half of it is lost in a few months of storage at slightly elevated temperature, through both degradation and polymerization. Some derivatives can lead to accelerated food browning or even generation of stable toxic compounds. Potential reactions and shelf-life testing are a critical consideration for products containing potassium sorbate.

Safety of potassium sorbate

The reason potassium sorbate is so widely used is because it generally thought to be safe for human consumption. In fact, it is even found naturally in certain berries – it was first extracted and isolated from the Rowan fruit.

In fact, in the appropriate matrices and concentrations, potassium sorbate is harmlessly metabolized by humans to produce carbon dioxide and water. However, in excess quantities it has been shown to potentially have cytotoxic and genotoxic properties, and can interfere with biological processes. Therefore, it is critical that potassium sorbate be kept below its legal limit in order to ensure safety.

Used properly, potassium sorbate can increase rather than decrease the safety of food, pharmaceuticals, and cosmetics by preventing growth of harmful species.

Novel applications

One innovation that takes advantage of the antimicrobial activity of potassium sorbate is the incorporation of this molecule into starch-based films for food packaging. Potassium sorbate, along with citric acid, is incorporated into edible food coatings. A plasticizer like sorbitol or glycerol may also be incorporated. These anti-microbial, food-safe films are able to inhibit growth of food-borne pathogens while otherwise preserving the quality and freshness of the food. These innovative films were demonstrated to be effective for storage and preservation of fruits and cheeses.

Conclusion

Potassium sorbate is widely used as a preservative in all types of products across the pharmaceutical, food, and cosmetics industries. It is effective in its activity against molds, yeasts, and certain bacteria. However, its use should be limited to acidic matrices and the concentration must be kept below the legal limit to reduce the risk of cytotoxic and genotoxic activity. Used properly, potassium sorbate can help to improve the quality and safety of everyday products.

References

Dehghan, Parvin, et al. “Pharmacokinetic and toxicological aspects of potassium sorbate food additive and its constituents.” Trends in Food Science & Technology 80 (2018): 123-130.

Versino, Florencia, et al. “Starch‐based films and food coatings: An overview.” Starch‐Stärke 68.11-12 (2016): 1026-1037.