Modified Tartary buckwheat (Fagopyrum tataricum Gaertn.) starch by gaseous ozone: Structural, physicochemical and in vitro digestible properties

The present study investigated the effects of gaseous ozone treatment on the structural, physicochemical and in vitro digestible properties of Tartary buckwheat starch (TBS). The results showed that gaseous ozone treatment increased the detectable carbonyl and carboxyl groups content, improved the amylose content, and decreased pH of TBS. The granule microstructures of native TBS and ozone-treated TBS (OTBS) were characterized by SEM, CLSM and small-angle X-ray scattering (SAXS), showing that OTBS exhibited a reduced granule smoothness and integrity, lessened coloration area of FITC fluorescent as well as decreased crystalline layer and increased amorphous region. FTIR and XRD results revealed that appropriate time of gaseous ozone treatment (2.5 and 7.5 min) enhanced short-range and long-range order structure due to the increased intermolecular oxidation cross-linking, whereas over treatment (15 and 20 min) caused degradation of the starch. With the increasing treatment time, apparent viscosity increased while breakdown viscosity, setback viscosity, swelling power and solubility decreased. OTBS exhibited a higher gelatinization enthalpy (ΔH) and a better viscoelasticity after gelation (6% OTBS gel, w/w ). Additionally, OTBS-2.5 and OTBS-7.5 showed a decreased rapidly digested starch (RDS) content and increased resistant starch (RS) content, indicating that the digestible properties of two oxidized starches was decreased, which provide a feasible way to develop TBS as a new modified starch source. • Gaseous ozone changed the granule morphology of Tartary buckwheat starch. • Ordered and double helices structures of starch were enhanced by moderate ozone. • The formation of more carbonyl and carboxyl groups in starch were detected. • The modified starches showed stronger gelling property and weaker retrogradation. • Moderate oxidized starch possessed lower digestibility than that of native starch.