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Presence of a Minor Amylose Fraction in the Central Portion of Waxy Wheat Starch Granules and Its Contribution to Granular Stability

¹Faculty of Home Economics, Laboratory of Food Technology, Kobe Women's University, Suma-Ku, Kobe City, Japan. ²National Agricultural Research Center for Western Region (WeNARC), National Agricultural Research Organization (NARO), Fukuyama, Hiroshima, Japan. Corresponding author. E-mail: seguchi@suma.kobe-wu.ac.jp ³National Institute of Crop Science, Kannondai, Tsukuba, Ibaraki, Japan.

When wheat starch granules containing various amounts of amylose (2.1–25%) were stained with 25% KI/10% I₂ solution, the granules largely changed to ghost structures below ≈5.0% amylose. The ghost showed a typical double structure: a black-brown central portion and a red-brown surrounding portion. The proportion of the black-brown central portion in the ghost was strongly correlated to the amylose content (%) in the starch, that is, the black-brown central portion decreased with a decrease in amylose. This suggests that amylose is possibly present in the black-brown central portion. Sonication (20 kHz) followed by centrifugation of the ghost separated the black-brown central portion from the red-brown surrounding portion, and the amylose content in each portion was determined. The results indicated that the amylose content in the black-brown central portion was 6.9%, whereas in the surrounding portion, it was only 1.0%. Furthermore, the central and surrounding portions were subjected to Sepharose CL-2B gel-filtration column chromatography and the presence of amylose could only be observed in the black-brown central portion.