Potassium sorbate is a preservative that is generally considered as relatively
safe. See
   http://www.soybean.com/ps.htm

as well as the following abstract:


Food Chem Toxicol 1992 Oct;30(10):843-851

The potential genotoxicity of sorbates: effects on cell
cycle in vitro in V79 cells and somatic mutations in
Drosophila.

Schlatter J, Wurgler FE, Kranzlin R, Maier P, Holliger E, Graf U

Sodium sorbate, potassium sorbate and an oxidation product of sodium
sorbate, 4,5-epoxy-2-hexenoic acid, were tested for their genotoxic
potential in cultured V79 Chinese hamster cells and in somatic cells of
Drosophila melanogaster (wing spot test, SMART). In Drosophila only the
epoxide showed a weak genotoxic effect. In V79 cells, freshly prepared
sodium sorbate solutions at the highest concentrations only (2.5 mg/ml, 24
hr exposure) arrested mitosis at the G2/M cell cycle phase and potassium
sorbate (2.5 mg/ml) had no effect. This arrest was reversible after a 24-hr
recovery interval. Sodium sorbate solutions stored for up to 208 days were
cytotoxic at 2.5 mg/ml, induced cell cycle arrest in the G2/M phase and
increased cellular protein content, indicating an action similar to spindle
poisoning and a chemical stress reaction (adaptation processes,
modification of transcription). Potassium sorbate solutions stored for 28
days were also cytotoxic. With 4,5-epoxy-2-hexenoic acid at
concentrations up to 0.01 mg/ml no effects were seen. At higher
concentrations (at least 0.1 mg/ml) cell killing was observed, which
probably resulted from unphysiologically lowered pH in the culture
medium. Overall, the results are interpreted as an indication of a weak
genotoxic potential of stored sodium sorbate solutions. Thus, sorbic acid
and its potassium salt at the concentrations used for food preservation can
still be considered as safe for human consumption.