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-mu-m, potassium sorbate permeability increased from 2.3 x 10(-10) to 2.0 x 10(-8) (mg/sec cm2)(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 x 10(-8) to 9.1 x 10(-10) (mg/sec cm2)(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%.