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Effect of Freeze-Thaw Cycles on the Gluten Fibrils and Crumb Grain Structures of Breads Made from Frozen Doughs

¹National Food Research Institute, Tsukuba Science City, Ibaraki 305-8642, Japan. ²Tsukishima Foods Industry Co., Ltd., 3-17-9, Higashikasai, Edogawa-ku, Tokyo 134-8520, Japan. ³Agriculture, Forestry and Fisheries Technical Information Society, Seifun-kaikan 6F, 15-6, Kabuto-cho, Nihonbashi, Chuo-ku, Tokyo 103-0026, Japan. ⁴National Institute of Agrobiological Sciences, Tsukuba Science City, Ibaraki 305-8602, Japan. ⁵Corresponding author. Phone: +81-29-838-8057. Fax: +81-29-838-7996. E-mail: naito@nfri.affrc.go.jp

The effects of freeze damage on the crumb grain and on the underlying gluten fibrils of baked breads were studied using scanning electron microscopy (SEM) and magnetic resonance imaging (MRI). Sweet and white bread doughs were stored at -20°C and subjected to freeze-thaw cycles. SEM images of grain pore walls that were washed with distilled water (20°C) clearly showed that gluten fibrils forming the skeletal framework of pore walls were cut and became coarse and nonuniform strings and that many knots were generated on gluten fibrils from freeze damage. An increase in the number of freeze-thaw cycles increased both the coarseness of the gluten fibrils and the size of the knots, although the apparent damage was not clearly detected on the crumb grain with MRI.