Study of Internal Structure of Waxy Wheat Starch Granules by KI/I₂ Solution

Abstract

Wheat starch granules were separated from waxy wheat flour by the acetic acid (pH 3.5) fractionation technique. Waxy wheat starch samples were stained red‐brown using KI/I2 solution. Subsequently, the concentration of the KI/I2 solution was increased to >2.5% KI and 1.0% I2. Then the appearance of the waxy wheat starch granules quickly became ghostlike. The internal structure of the ghost could be observed. This structure consisted of two parts with different colors: a red‐brown central part and a slightly pinkish surrounding part. Sonication of the ghost at 20 kHz for 20 sec separated the central part from the surrounding part. Each of the separated parts were subjected to gel‐filtration chromatography, and their chromatography profiles indicated only amylopectin and no amylose. The central and surrounding parts had molecular weights of 54.3 × 105 and 23.8 × 106 from Berry plots, respectively.

Ghosts of B‐type Wheat Starch Granules in Concentrated KI/I2 Solution

“…1-3). It was reported by Seguchi et al [1] that waxy wheat starch granules (A-type) showed a remarkable double structure of black-brown central and red-brown surrounding portions, however, this was not observed in B-type waxy wheat starch granules. Twelve kinds of B-type starch granules containing various amounts (2.1,25.0%) of amylose were treated with concentrated KI/I 2 solution, and the relative ghost areas were measured (Tab.…”

“…The concentrated KI/I 2 solution was prepared as follows; KI (25 g) was dissolved in 10% I 2 solution and finally filled up to 100 mL with the same solution. Microphotographs of the B-type starch ghosts were taken as described by Seguchi et al [1].…”

“…It is known that waxy wheat starch granules change to the ghost form in concentrated KI/ I 2 solution (25% KI/10% I 2 solution), but nonwaxy wheat starch granules do not show the ghost form in the same treatment, which suggests that the amylose molecule plays an important role in the structural stability of the starch granule [1]. This ghost phenomenon of the waxy wheat starch granule in concentrated KI/ I 2 solution has also been observed in waxy barley, rice, maize, proso millet, and foxtail millet starch granules [2].…”

“…The importance of the role of the amylose molecule in the stability of barley and rice starch granules was reported by Yasui et al [3] and Seguchi et al [4], respectively. However, waxy wheat starch granules have a peculiar nature, showing a remarkable double structure in the ghost, that is, a black-brown central portion and red-brown surrounding portion [1]. Hayashi et al [5] showed that the amylose molecules were mainly present in the central portion of the ghost, as indicated by the data of determination of amylose content and column chromatography profiles, and that the ghost central portion is more rigid in the concentrated KI/I 2 solution than the surrounding portion.…”

Starch Properties of a Waxy Mutant Line of Hull-less Barley (Hordeum vulgare L.)

“…Moisture content was calculated as weight loss after drying at 135 °C for 1 h. Starch granules were stained with 10% iodine-25% potassium iodide solution and microscopically observed as reported [9].…”