The fractional release (MF,t/MP,0) versus time curves in Fig. 4 was obtained by fitting Equation (2) to the experimental data.
It shows the migration of thymol from PBS films with various incubation times and food simulants i.e. distilled water, acetic acid, isooctane, ethanol 10% and ethanol 95%. Good agreements were obtained between experimental data and proposed model prediction. This suggested that the release kinetic could be described by the Fick's law of diffusion. With increasing the incubation time, thymol was rapidly migrated from PBS into the food simulants. It required 50e60 h to reach equilibrium at all food simulants studied. The type of food simulants were expected to be the key factor which influence the migration [20]. At thermodynamic equilibrium, isooctane allowed thymol to migrate with the largest fractional release at around 0.8. This was expected because of their identical polarity.