Department of Materials Science and Engineering, University of Maryland, College Park, Maryland20742, United States.
NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland20899, United States.
Biomacromolecules. 2023 May 8;24(5):1980-1993. doi: 10.1021/acs.biomac.2c01240. Epub 2023 Jan 30.
In this study, as-is (ca. 12% moisture by mass) and hydrated (50% water by mass) granules of waxy potato (WP), waxy wheat (WW), waxy maize, normal maize, and high-amylose maize (HAM) starches were investigated by using small-angle neutron and X-ray scattering (SANS and SAXS), wide-angle X-ray scattering, and ultra-small-angle neutron scattering. The SANS and SAXS data were fitted using the two-phase stacking model of alternating crystalline and amorphous layers. The partial crystalline lamellar structures inside the growth rings of granules were analyzed based on the inter-lamellar distances, thicknesses of the crystalline lamellae and amorphous layers, thickness polydispersities, and water content in each type of layer. Despite having a longer average chain length of amylopectin, the WP and HAM starches, which had B-type allomorph, had a shorter inter-lamellar distance than the other three starches with A-type allomorph. The WP starch had the most uniform crystalline lamellar thickness. After hydration, the amorphous layers were expanded, resulting in an increase of inter-layer distance. The low-angle intensity upturn in SANS and SAXS was attributed to scattering from interfaces/surfaces of larger structures, such as growth rings and macroscopic granule surfaces. Data analysis methods based on model fitting and 1D correlation function were compared. The study emphasized─owing to inherent packing disorder inside granules─that a comprehensive analysis of different parameters was essential in correlating the microstructures with starch properties.
在这项研究中，使用小角中子和 X 射线散射（SANS 和 SAXS）、广角 X 射线散射和超小角中子散射对非糯马铃薯（WP）、糯小麦（WW）、糯玉米、普通玉米和高直链淀粉玉米（HAM）淀粉的原粒和水合颗粒（含水量为 50%）进行了研究。使用两层交替结晶层和无定形层的两相堆积模型对 SANS 和 SAXS 数据进行了拟合。基于层间距离、结晶层和无定形层的厚度、结晶层厚度多分散性以及每层的含水量，分析了颗粒生长环内部分结晶层状结构。尽管 WP 和 HAM 淀粉的支链淀粉平均链长较长，但具有 B 型变体的两种淀粉的层间距离比具有 A 型变体的另外三种淀粉短。WP 淀粉的结晶层状厚度最均匀。水合后，无定形层膨胀，层间距离增加。SANS 和 SAXS 中的低角度强度上翘归因于较大结构（如生长环和宏观颗粒表面）的界面/表面的散射。对基于模型拟合和一维相关函数的数据分析方法进行了比较。研究强调了由于颗粒内部固有的堆积无序性，必须综合分析不同参数，才能将微观结构与淀粉性质联系起来。
