Sorbic Acid and Potassium Sorbate Permeability of an Edible Methylcellulose‐Palmitic Acid Film: Water Activity and pH Effects

The apparent permeability constants for potassium sorbate and sorbic acid through an edible film composed of methylcellulose and palmitic acid (weight ratio 3:1) were evaluated as a function of water activity (a w ) and pH. For films with thickness 55–66 μm, potassium sorbate permeability increased from 2.3 × 10 −10 to 2.0 × 10 −8 (mg/sec cm 2 )(cm)/(mg/mL) as a w increased from 0.65 to 0.80. Films were not stable at a w levels above 0.80. Permeability of the film to sorbic acid at a w 0.8 decreased from 3.3 × 10 −8 to 9.1 × 10 −10 (mg/sec cm 2 )(cm)/ (mg/mL) as pH increased from 3 to 7. At pH 3 the undissociated acid was 97.5% and at pH 7 it was 0.4%.