Water Diffusion in Buckwheat Noodles and Wheat Noodles during Boiling and Holding as Determined from MRI and Rectangular Cylinder Diffusion Model

Magnetic resonance imaging (MRI) was employed to observe water diffusion within two kinds of buckwheat noodles (marunuki, sarashina) and one kind of wheat noodle during boiling and holding. The apparent diffusion coefficients for water were statistically estimated with Fick's second law using a rectangular cylinder model, and the changes in moisture distribution in buckwheat and wheat noodles were compared quantitatively. Apparent diffusion coefficients of water in noodles during boiling were 4 to 7 x 10(-6) cm(2)/sec. The diffusion coefficients of water in buckwheat noodles during boiling were higher than those in wheat noodles. For each noodle, the diffusion coefficient during holding after boiling was 2 to 3 x 10(-7) cm(2)/sec and constant through the holding time, from 30 to 120 min. The diffusion coefficients in buckwheat noodles during holding were lower than those in wheat noodles. These results show that, as compared with wheat noodles, buckwheat noodles cooked more rapidly and lost favorable texture during holding.