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Development of a Novel Staining Procedure for Visualizing the Gluten–Starch Matrix in Bread Dough and Cereal Products

¹Food Research Center, Nisshin Foods Inc., 19-12 Koami-cho, Nihonbashi, Chuoku, Tokyo, 103-8544, Japan. ²Corresponding author. Phone: +81-3-5641-8041. Fax: +81-3-5641-8814. E-mail: maedatat@mail.ni-net.co.jp ³Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1, Yayoi, Bunkyo Ward, Tokyo, 113-8657, Japan. ⁴Department of Biological Chemistry and Food Science, Faculty of Agriculture, Iwate University, 3-18-8, Ueda, Morioka, Iwate, 020-8550, Japan. ⁵Department of Applied Chemistry, Faculty of Engineering, Kogakuin University, 2665-1, Nakano-machi, Hachioji, Tokyo, 192-0015, Japan. ⁶Food Kansei Communications Corp., Toa-mansion No. 103, 4-24-7 Sendagi, Bunkyo Ward, Tokyo, 113-0022, Japan.

A novel staining procedure has been developed to visualize the gluten– starch matrix in wheat flour dough. Dough samples mixed to the final stage were stained with 26 fluorescent reagents, and each stained sample was observed with three sets of fluorescence filters (blue, green, and red). Of all the combinations of reagents and filters, the combination of acid magenta and the blue fluorescent filter set was the most effective in distinguishing starch granules from gluten network structure. Its effectiveness was further demonstrated with gluten and starch granule samples, in which the contrast was clearer when observed with the blue fluorescent filter set than without any fluorescent filter. Visualizing the gluten–starch matrix in dough samples at four mixing stages with the same procedure resulted in clear identification of the changes in gluten network structure because of the differences in mixing stages. The same procedure also enabled us to distinguish starch from gluten in white salted noodles, baked cookies, and flour particles. The proposed procedure is quicker, simpler, and has a lower risk of altering the sample than other conventional ones, and it is expected to become a useful tool in cereal studies.