| Eight polished oat grains were collected from different typical locations in China, and the starch was extracted from oat grains using alkali-extraction method. The multi-scale structures and function characteristics of oat starches were systematically studied by optical/polarizing microscope (OM/PM), scanning electron microscope (SEM), small/wide angle X-ray scattering (SAXS/WAXS), X-ray diffraction (XRD), gel permeation chromatography (GPC) and anion exchange chromatography (HPAEC), rapid viscometer(RVA) and differential scanning calorimeter (DSC), and other physical and chemical methods. The digestion curve of oat starch was fitted using first-order kinetics equation and using LOS (Logarithm of Slope) plots to give the digestion rate (k) and end point concentration (Ct),and then discussed relationship between the digestion rate and fine structure of oat starches. Besides, we also studied the effect of tea polyphenols and P-glucan as a model system on inhibition of starch digestibility. The results of the study are as follows:(1) The molecular, aggregative, granular structure and properties of oat starch were systematically studied by different method, and the results of correlation analysis found that there was a positively correlation between starch gelatinization temperature (Tp) and content of long amylopectin. Peak viscosity (PV) and relative crystallinity (RC) were positively correlation, and negatively correlation with the thickness of the amorphous layer.Setback (SB) and the distribution of short amylopectin was a positive correlation, and the distribution of the long amylopectin showed a negative correlation. Slow digestion of starch(SDS) was positively correlation with distribution of short amylopectin. Solubility (S) and crystallization layer thickness was a positive correlation.(2) This study confirmed that the starch gelatinization is a process of multiple phase change by studying thermal property, swelling power, solubility, lamellar structure and crystalline structure of oat starch during heating processing. Before onset temperature (To),the swelling power of starch granules increased, the order of starch lamellar structure reduced,and the area of crystallization decreased. When over To, the swelling power of starch granules almost uncharged and then rapid increased, the polarization cross of starch disappeared, the lamellar structure of starch damaged, and the crystallization peak of starch disappeared.(3) The LOS plot was used to study the digestion property of oat starches, and GPC and HPAEC were used to characterize fine structure of amylose and amylopectin. Some oat starches had a slower digestion rate than rice starch, which may account for oat starches had higher amylase content, larger size of amylose. However, the lower proportion of the longest chains in oat starches may increase the digestion rate of oat starches.(4) Certain proportion of tea polyphenols were added into different starch digestion phase, found that tea polyphenols can restrain the digestion property by combined with starch or digestive enzyme. Fluorescence quenching and docking showed that tea polyphenols had obvious inhibitory effect on digestive enzymes, which may mainly account for tea polyphenols combined with amino acid residues of digestive enzymes.Consequently, tea polyphenols reduced the digestion property of the starch.(5) This study revealed the influence of ?-glucan on digestion rate of oat starch by adding different concentrations and molecular weight of ?-glucan. Rheological results indicated that the system viscosity increased with the concentration and molecular weight of ?-glucan. Thus, the digestibility of oat starch were decreased due to ?-glucan. And the SEM results showed that ?-glucan of high molecular weight will form a layer of film in the surface of starch, further reduce the digestibility of oat starch. |
PDF Full Text Request