Effects Of Ultrafine Grinding On Structural And Physicochemical Properties Of Coarse Cereal And Bean Starch

Native starch of coarse cereal and bean has properties such as insoluble in water, easy to retrogradate and so on, which greatly limits its wider application. Investigating changes ultrafine grinding leading to starch helps us understanding and exploring structural and physicochemical properties of coarse cereal and bean starch more systematically and provides a theoretical basis for deep processing of coarse cereal and bean starch. Influence and variation on physicochemical properties of coarse cereal and bean starch were investigated with different ultrafine grinding time on the basic of comparing structural and physicochemical properties among eight kinds of coarse cereal and bean starch. The main conclusions were as follows:(1) Particle size of bean starch was 5 ~10 times bigger than that of coarse cereal starch, with reniform or ellipsoid shape, smooth surface, X-shaped or stellate polarization cross and C-type crystalline features. Coarse cereal starch granules showed normal or oblique polarization cross and typical A-type crystalline, while naked barley starch presented reniform or flattened circular shape and smooth surface and buckwheat starch, millet starch and broom corn millet starch showed irregular polygon shape. The content of amylose and iodine blue values of bean starch were higher than that of coarse cereal starch. As for water absorption and water released, japonica broom corn millet starch was the lowest and solubility and swelling power of all the starch increased with the temperature risen. The transparency of all the starch was significantly decreased with the extension of storage time and waxy broom corn millet starch presented the biggest value. The retrogradation rate of naked barley starch, broad bean starch and pea starch was faster than other starch while no retrogradation occurred on waxy broom corn millet starch. It had significant differences among all the starch about gelatinization and thermodynamic properties, while waxy broom corn millet starch had lower pasting temperature range and higher pasting temperature, peak temperature, end temperature and heat enthalpy.(2) Ultrafine grinding changed structural characteristics of all the starch significantly. All the starch granules began deformed after grinding 2 h with crystalline type changing, crystallinity was decreasing and diffraction peak smoothing or disappearing. After treatment with 4 h polarization cross of all the starch reduced significantly with diffraction peak disappearing completely. The structure of all the starch was destroyed entirely and begun reuniting after 6 h grinding.(3) Ultrafine grinding had little influence on iodine blue value of all the starch. Water absorption and retrogradation increased followed by fall, while solubility and swelling power increased with the extension of grinding time. Peak viscosity, trough viscosity, final viscosity, breakdown and setback of ultrafine grinding starch were below native starch, and decreased with the extension of grinding time, on the contrary, the transparency was above native starch and increased with the extension of grinding time. As for water released, naked barley starch, millet starch and broom corn millet starch rised while buckwheat starch and bean starch declined with the extension of grinding time. There was no significant endothermic peak of all the ultrafine grinding starch, with breaking of double helix structure and dry gelatinization of starch.There were significant differences of structure and physicochemical properties among all the starch, while ultrafine grinding had remarkable impact on structure and physicochemical properties of coarse cereal and bean starch and variation tendency was obvious with the extension of grinding time. Dry gelatinization occurred and structure destroyed which bring about the instability of structure and physicochemical properties with ultrafine grinding processing over 6 h, while grinding with 2 ~ 4 h was a more appropriate time since structure and physicochemical properties changed but certain morphological structure was maintained.