Determination of the diffusion coefficient of tissue, cuticle, cutin and wax of apple Original Research Article

The cuticle of apple basically consists of a cutin and wax layer in parallel each with different diffusion properties. Diffusion coefficients were determined for the apple cultivars ‘Jonagold’, ‘Jonagored’ and ‘Elstar’ to accurately describe moisture transport through the cuticular membrane. Separate diffusion coefficients were estimated for tissue, cutin and wax of each cultivar by fitting model predictions, obtained with the finite element method, to experimental moisture concentration data using a non-linear least squares procedure. Initial and boundary conditions for modelling diffusion were also determined in the same experiments. Conversion between moisture concentrations and water potentials was accomplished by means of equilibrium moisture content curves, which were experimentally determined for each cultivar. For all cultivars, diffusion coefficients ranged from 1.92×10−15 to 3.03×10−14 m2 s−1 for wax, from 4.03×10−14 to 7.16×10−14 m2 s−1 for cutin and from 4.33×10−12 to 1.12×10−11 m2 s−1 for tissue.