Potassium sorbate is a food grade preservative generally regarded as safe (GRAS) worldwide. It is the inactive salt of sorbic acid. It readily dissolves in water where it converts to sorbic acid, its active form, at a low pH. Sorbic acid is very pH dependent. While it shows some activity up to pH 6 (about 6%), it is most active at pH 4.4 (70%). At pH 5.0 it is 37% active. As sorbic acid, it is considered to be active against mold, fair against yeast and poor against most bacteria. Sorbic acid is an unsaturated fatty acid and as such is subject to oxidation (use of an antioxidant like Mixed Tocopherols T50 is recommended). It is also sensitive to UV light and may turn yellow in solution. Gluconolactone is reported to stabilize potassium sorbate against discoloration and darkening in aqueous solutions and may be useful in stabilizing sorbic acid in the water phase of a product.
While sorbic acid is naturally occurring in some fruits (like the berries of the mountain ash), virtually all of the world’s production of sorbic acid, from which potassium sorbate is derived, is manufactured synthetically, and is a nature-identical compound chemically equivalent to the molecule found in nature. It is a widely used preservative in food production, but cannot be considered “natural” (no matter what you’ve heard!).
Sorbic acid can cause contact dermatitis at concentrations above or below 0.5%. Studies show that if it is used at a concentration of no more than 0.2% it is unlikely to constitute a safety hazard.
Potassium sorbate is not a broad spectrum preservative for cosmetic use and should be combined with other preservatives. If potassium sorbate is used as a preservative, the pH of the finished product may need to be reduced for potassium sorbate to be effective. This is because potassium sorbate is the inactive salt form of sorbic acid. To be useful, the pH of the formulation must be low enough to release the free acid for useful activity.
Following is a chart to of the relative activity at various pH:
|pH||% Active Sorbic Acid|
At temperatures above 60°C (140°F), potassium sorbate can begin to sublime. Add to the water phase of formulations at a temperature below 60°C (140°F). If adding it after oil and water phases have been combined, predissolving the required potassium sorbate in a portion of the water phase will make it easier to incorporate into the formed emulsion.
The above information is for general research purposes only and is not a representation or warranty of any kind. This material is not intended to diagnose, treat, cure or prevent any disease. The user of this material is solely responsible for determining fitness for any particular use; requesting and reviewing the applicable Material Safety Data Sheet; and compliance with all applicable laws and regulations. Terms and conditions apply