Moisture Diffusion Coefficients of Single Wheat Kernels With Assumed Simplified Geometries: Analytical Approach

Using a combination of soaking data and an analytical solution of the diffusion equation, moisture diffusioncoefficients of single wheat kernels were determined for nine commercial varieties representing six market classes of U.S.wheat. Two geometric conditions, the whole kernel as a prolate spheroid, and the endosperm (also modeled as prolatespheroidal) and pericarp as separate components, were examined. Values from the analytical solution for a sphere wereadjusted by a geometrical correction factor to more closely represent the response of a prolate spheroid. The ranges indiffusion coefficients were 0.39 10 10 to 1.04 10 10 m 2 /s for endosperm and 0.04 10 10 to 0.28 10 10 m 2 /s forpericarp. Compared to the pericarp, moisture diffused more rapidly in the endosperm. Soft wheats tended to have a morepermeable pericarp layer than hard wheats, which resulted in a greater overall rate of diffusion, despite the endosperm ofthese two groups being nearly equivalent in diffusion coefficient value.