Abstract:To understand the relationship between the multi-scale structures of rice starch and its digestibility before and after heat-moisture treatment (HMT), the digestibility levels of rice starch before and after HMT were determined by in vitro simulation HMT-induced alterations in the multi-scale structures of rice starch were evaluated by small-angle X-ray scattering, X-ray diffraction, and gel permeation chromatography coupled with multi-angle light scattering. The study showed that the degree of the semi-crystalline lamellae order, relative crystallinity, and molecular weight of rice starch were reduced by HMT. Additionally, damage to the crystalline, lamellar, and chain structures inside the starch granules, formation of V amylose-lipid complex, decreased levels of high-molecular weight (Mw>2×107 g/mol) fragments, and an increased proportion (0% to 21.3%) of low-molecular weight (Mw<5×106 g/mol) fragments favored the formation of slowly digestible starch and resistant starch.. However, when the proportion of the starch fragment with Mw<5×106 g/mol was increased to 32.1%, excess low-molecular weight fragments lead to the formation of rapidly digestible starch. The results provide a theoretical basis and basic data for the adjustment and control of the digestibility of novel functional starch and/or starchy products by using HMT.
