MOISTURE DIFFUSION IN A DRY SOYBEAN SEED MEASURED USING PULSED-FIELD-GRADIENT NMR

Moisture diffusion coefficient in a dry soybean seed was measured by a pulsed field gradient NMR method using stimulated echoes. A constant diffusion coefficient of 4.3 x 10(-10) m2 s-1 was obtained for diffusion times ranging from 18.5 ms to 28.5 ms. This value is 10 times larger than literature values measured by a gravimetric method of seed hydration, and is 100 times larger than that calculated using absorption and desorption data. With the aid of NMR imaging, it was revealed that a dry soybean seed had considerable freely movable water which was centred at the intercotyledon face surrounded by an oil layer. The discrepancy in diffusion coefficients between those measured by NMR and by the gravimetric method is discussed. When the diffusion time was extended over 38.5 ms to 113 ms, a clearly restricted feature of diffusion was observed