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Moisture Distribution and Diffusion in Cooked Spaghetti Studied by NMR Imaging and Diffusion Model

¹National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki, 305-8642, Japan. ²Graduate School of Pure and Applied Science, University of Tsukuba, 1-1-1, Tennoudai, Tsukuba, Ibaraki, 305-8571, Japan. ³Research Center for Basic Science, Research and Development, Quality Assurance Division, Nisshin Seifun Group Inc., 5-3-1 Tsurugaoka, Fujimino, Saitama 356-8511, Japan. ⁴Present address: Food Research and Development Center, Nisshin Foods Inc., 5-3-1 Tsurugaoka, Fujimino, Saitama 356-8511, Japan. ⁵Corresponding author. Phone: +81-29-838-8033. Fax: +81-29-838-7996. E-mail: mitsuru@affrc.go.jp

Moisture diffusion in spaghetti during boiling and holding after boiling was analyzed with a cylinder diffusion model based on moisture content mapped by magnetic resonance imaging. The images showed water penetrating concentrically in the cross section of a cooked spaghetti strand. The moisture profiles calculated from the images refracted near the central part in undercooked spaghetti due to the presence of ungelatinized starch. The moisture profiles of the samples with different holding times intersected around one-third of the radius from the surface. The slope of the moisture profile decreased along with the holding time while the moisture content at the intersection remained unchanged. The diffusion coefficients were determined statistically for the fully gelatinized region with a cylinder model. The theoretical moisture profiles calculated using such coefficients fitted very well to experimental data. The diffusion coefficients of dried spaghetti were smaller than those of fresh spaghetti at both boiling and holding periods, suggesting that the moisture transport property had been reduced by the drying process during manufacture of spaghetti. The diffusion coefficients decreased with increases in boiling and holding times. The diffusion model with a constant diffusion coefficient is, therefore, valid in a limited boiling or holding time.