| Millet is one of the important staple grains in China,and starch is its main component.In order to improve the processing characteristics of millet,improve the digestibility of its starch,and expand the application range of convenient food of millet,twin-screw extrusion was utilized to process raw millet materials.Firstly,effects of water content of Millet（that is 12%,14%,16%and 18%respectively）and temperature of the fourth zone during extrusion（that is 140℃,150℃,160℃and 170℃）on physicochemical properties and digestibility of millet starch were studied by evaluating solubility,swelling power,gelatinization characteristics and thermodynamic properties,also combined with structural characterization such as Fourier infrared spectroscopy,X-ray diffraction and scanning electron microscopy;Secondly,the extruded millet sample（with moisture content of 14%and temperature of 160℃in the fourth zone during extrusion）was selected,followed by fractionation of albumin,globulin,glutenin and gliadin,and latter,effects of extrusion treatment on the physicochemical properties and structure of millet protein were analyzed by comparing with that of fresh millet protein;Finally,Effects of lipid and protein components on the physicochemical properties and digestibility of millet starch were further explored.Results showed that the content of amylose and the solubility of millet starch increased and the swelling power decreased with the increase of water content of millet flour and the increase of temperature in the fourth zone;The gelatinization characteristics of millet starch were changed,including the significant decrease of peak viscosity,disintegration value and retrogradation value,the increase of gelatinization temperature,and the disappearance of starch absorption peak in the thermodynamic diagram of DSC;The swelling treatment will also change the rheological properties of millet starch.The temperature scanning shows that the elastic modulus（G’value）and viscosity modulus（G’value）of millet starch will increase,and the frequency scanning results show that the tanδvalue decreases,that is,the deformation resistance increases;Extrusion treatment increased the content of slow digested starch and resistant starch;The crystallinity of millet starch decreased,the position of 2θangle diffraction peak changes,the crystal shape changed from A-type to V-type,and the grain structure cracked in different degrees.The most significant change was when the moisture content of millet flour was 18%and the temperature in the fourth zone was 170℃.Secondly,the solubility,water retention and emulsification of albumin,globulin,glutenin and gliadin in millet decreased and the emulsification stability increased after extrusion and extrusion treatment.Fourier transform infrared spectroscopy（FTIR）showed that the positions of absorption peaks in the wave number range of 3300～3600 cm-1 moved to the left,the contents of secondary structures changed,the surface hydrophobicity of the four proteins decreased significantly,the fluorescence intensity decreased and the peak wavelength shifted to the left.Finally,the results of the interaction between millet protein and starch showed that millet protein components had a great influence on the solubility and gelatinization properties of millet starch,and deproteinization increased the hydrolysis rate of starch to varying degrees,but did not change the crystal form of starch. |
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