PARAMETER-ESTIMATION FOR MOISTURE TRANSPORT IN APPLES WITH THE AID OFNMR IMAGING

The moisture diffusivity of Jonagold apple flesh and skin was estimate d based on NMR images obtained from drying experiments. It was assumed that the diffusivities were not dependent on the moisture concentrati on. A multi-echo sequence was required to correct for the change of T- 2 during the experiment. The diffusivities were estimated by minimizat ion of the squared error between measured and predicted moisture conce ntrations. The latter were calculated based on the analytical solution or a Galerkin finite element discretization of the diffusion equation . The average flesh diffusivity was 10.3 x 10(-11) m(2) s(-1) and did not change significantly during ultra-low oxygen storage. The correspo nding skin diffusivity was 1.32 x 10(-13) m(2) s(-1). If the flesh and skin diffusivity were estimated simultaneously, the values were 2.8 x 10(-12) and 6.3 x 10(-15) m(2) s(-1), respectively.