Effect Of Extrusion On The Structure Of Millet Protein

Millet(Setaria italica(L.)Beauv.var.germanica(Mill.)Schrad.)is a high nutritional value cereal and a good source of nutrition.The extrusion technology improves the product characteristics by controlling different processes such as mixing,heating,cooking,shearing and molding,and realizes the development of products with better nutrition,function and sensory characteristics.In this study,the extraction conditions of the four protein components were optimized in millet.The millet powder was subjected to extrusion treatment.SDS-polyacrylamide gel electrophoresis(SDS-PAGE),scanning electron microscopy(SEM),differential scanning calorimetry(DSC),ultraviolet spectrum,fluorescence spectrum,fourier transform infrared spectroscopy(FTIR)were used to analyze the characteristics of four protein components in millet.The research results are as follows:(1)Scanned electron microscope image shows that the prolamin,albumin and globulin molecules are closely linked and exist in an aggregate state,while the gluten molecules are loo sely connected and have a smooth surface.A certain degree of aggregation and fusion of prolamin,albumin and globulin after extrusion,and the gluten is aggregated and the shape changes from spherical shape to cube-like shape,which changes from a dispersed distribution to a certain regularity and sequential distribution.During the extrusion process,the globulin was denatured at 72.36 °C.The denaturation temperature of the prolamin was the highest,reaching 110.67 °C.Its protein structure was more stable than the other three proteins.The enthalpy of globulin is smaller than the other three protein components,so the globulin is more susceptible to denaturation after reaching the denaturation temperature.(2)It was observed from the SDS-PAGE image that the prolamin is composed of a low molecular weight subunit(11-25 k Da)with three distinct bands,?-prolamin,?-prolamin,and ?-prolamin.The three bands still exist after extrusion,and the number of subunit strips has not changed.The subunits of albumin,globulin and glutenin are widely distributed(11-180 k Da).Albumin contains the largest number of subunits,and the subunit bands of the three protein components were significantly reduced after extrusion.(3)It was found by fourier transform infrared spectroscopy that there are ?-helix,?-sheet,?-turn,?-anti-parallel folding and no random coil structure was found in the secondary structure of the millet protein components.Among the four protein components,the content of the main structure of the four protein components is ?-sheet structure,followed by the ?-helix and ?-turn,and the ?-anti-parallel folding is the lowest.The content of secondary structure of each proteincomponents changed after extrusion.The content of ?-helical structure in the four protein components increased,the content of ?-sheet decreased.The ?-turn and ?-anti-parallel folding content of albumin increased.The ?-turn and ?-anti-parallel folding content of the other three protein components decreased.Ultraviolet and fluorescence spectrum showed that the ?max of the absorption peaks of ultraviolet spectrum and the emission peaks of fluorescence spectrum in the four protein components occurred blue shift after extrusion with the intensity of absorption and emission decreased.The side chains of aromatic amino acid molecules were gradually buried inside the protein,the polarity of the environment is gradually reduced and the surface hydrophobicity of the protein decreases with the spatial conformation of the protein changes.The images obtained by scanning electron microscopy,the relative molecular mass showed that the extrusion has little effect on the secondary structure of prolamin,the other three protein components vary from the subunit composition,and the tertiary structure has taken place a large change.(4)The water holding capacity and surface hydrophobicity of the four protein components were determined.It was found that gluten had the highest water holding capacity,followed by prolamin,globulin and albumin.The water holding capacity of the four protein components after extrusion decreased were due to the tertiary structure of the four protein components is destroyed.Gluten has the greatest decline,from 5.92 g/g to 1.30 g/g.It may be due to the tertiary structure of gluten has not only destroyed but its subunit structure is also destroyed,making it impossible to retain more water molecules.The results of ultraviolet and fluorescence spectroscopy showed that the hydrophobicity index of the four protein components decreased after extrusion,which was the same as the direct measurement.