The purpose of this study was to understand the ordered structure of starch in rice flour based on a physical modification with non-heating, milling, and water sorption through the structural evaluation of rice flour using small-angle X-ray scattering (SAXS) and infrared spectroscopy within the 4000–100 cm⁻¹ region. The SAXS pattern of the samples with low moisture contents subjected to milling yield a band within the 0.4–0.9 nm⁻¹ of the q range owing to a lamellar repeat of starch with an ordered structure in rice flour. We proposed an order parameter using the intensity of the SAXS band to quantify the order structure of starch in rice flour, and the true density was negatively correlated with the order parameter. Infrared band at 990 cm⁻¹ in COH bending mode applied to the hydroxyl group of C6 shifted to a low wavenumber corresponding to the order parameter. A linear correlation was found between the order parameter and the 990 cm⁻¹ and band at 861 cm⁻¹ owing to COC symmetrical stretching of glycoside bond and CH₂ deformation of the glucose unit of starch, 572, 472, and 436 cm⁻¹, owing to the pyranose ring in the glucose unit of starch. The identified infrared bands are effective for quantifying the ordered structure of starch at the lamellar level. When subjected to water sorption, the band position at 990 cm⁻¹ shifted to a higher wavenumber above a water activity of 0.7. This result revealed that the water-induced transition of glass to rubber of starch in rice flour can be clearly evaluated through infrared spectroscopy using the band at 990 cm⁻¹. In addition, the band at 861 cm⁻¹ also shifted to a higher wavenumber, whereas those at 572 and 436 cm⁻¹ did not show a significant shift. These results indicate that water sorption slightly affects the internal structure and may mainly affect the surface of starch.

本研究的目的是通过使用小角度 X 射线散射 (SAXS) 和4000-100 cm ^-1区域内的红外光谱。由于米粉中具有有序结构的淀粉的层状重复，经过研磨的低水分含量样品的 SAXS 模式在q范围的 0.4-0.9 nm ^-1内产生一条带。我们提出了一个利用SAXS波段强度的有序参数来量化米粉中淀粉的有序结构，真密度与该有序参数呈负相关。990 cm ^-1处的红外波段在应用于 C6 羟基的 COH 弯曲模式中，转换为对应于有序参数的低波数。由于糖苷键的 COC 对称拉伸和淀粉葡萄糖单元的CH ₂变形，572、472 和 436 cm ^-1的顺序参数与 990 cm ^-1和 861 cm ^{-1 的}谱带之间存在线性相关性，由于淀粉葡萄糖单元中的吡喃糖环。确定的红外波段可有效量化层状水平的淀粉有序结构。吸水时，谱带位置在 990 cm ^-1转移到高于 0.7 的水活度的更高波数。该结果表明，通过使用 990 cm ^-1波段的红外光谱，可以清楚地评估米粉中淀粉由水诱导的玻璃向橡胶的转变。此外，861 cm ^-1处的波段也移动到更高的波数，而572和436 cm ^-1处的波段没有显示出明显的移动。这些结果表明吸水对内部结构的影响很小，可能主要影响淀粉的表面。