Читать книгу Whole Grains and Health - Группа авторов - Страница 66

Granular starch is the most abundant material in whole grains with variation of size shape, and surface properties depending on its source and processing treatment (Krok et al. 2000). Starch granules have different levels of structural features and the granule is a semi‐crystalline material. Whole grain cereal and pseudocereal (quinoa and amaranth) starches are of the A‐type showing peaks at 2θ of 9.9, 11.2, 15, 17, 18.1 and 23.3°, which differentiates them from B‐type tuber starches showing peaks at 5.6, 15, 17, 22 and 24°. A‐ and B‐type starches reflect the difference in the geometry of their unit cells, the packing density of double helices and the amount of bound water within the crystal structure (Buléon et al. 1998; Qian and Kuhn 1999). When starch is gelatinized and dispersed, the linear amylose (essentially α‐(1→4) linked) and highly branched amylopectin [containing both α‐(1→4) and α‐(1→6) linkages] can be separated by their structural difference and size. The percentage of α‐(1→6) linkage is one aspect of the fine structure of amylopectin, for example, 4.6% for normal maize starch and 5.7% for waxy maize starch (Shin et al. 2008).