Research On Comparison Of Functional Properties Of Soy Protein Isolate Prepared By Different Saccharification Methods

The functional properties of protein can be improved by Maillard reaction,so the soy protein isolate(SPI)and dextran(DX)were selected for saccharification reaction as raw materials,there were two kinds of saccharification reactions,including wet and dry ways.However,dry way usually costed a long time,therefore,the wet method was used to prepare the SPI-DX conjugates.The SPI-DX conjugates were prepared by water bath and microwave treating,which belong to wet ways.The process conditions were optimazed by response surface;The gel electrophoresis,fourier transform infrared spectroscopy,raman spectroscopy,internal fluorescence spectroscopy and scanning electron microscopy were used to analyze the subunit structure,secondary structure and tertiary structure.The solubility,emulsifying property,foaming property and surface hydrophobicity of SPI-DX conjugates were measured as well.Moreover,the effect of different saccharification methods on the functional properties of SPI-DX conjugates and the relationship with the structural changes were explored.The main results were as follows:The SPI-DX conjugates were prepared by water bath method and microwave method.Taking the grafting degree as the index,and get the optimal SPI-DX conjugates' process parameters by response surface method.The parameters of water bath group was prepared by 82 min of wter bath time and 91?of temperature and the SPI and DX was at 1:1 weight ratio,the degree of conjugates was 43.56%;and the parameters of microwave group was prepared by 93 s of microwave time and 630 W of microwave power and the SPI and DX was at 1:1 weight ratio,the degree of conjugates was 49.43%.In this study,the prepare conditions which resulted in similar graftings of SPI-DX conjugates with two methods were employed,and then the functional properties were measured.Comparing with the original SPI,the SPI-DX water bath group and the SPI-DX microwave group had an obvious effect on the solubility,foaming property,emulsifying property and surface hydrophobicity.The solubility and foaming ability of the SPI-DX mixed group showed the opposite trend,the emulsifying properties and surface hydrophobicity had no obvious change,while the foaming stability had a great increase.The SPI-DX water bath group obviously increased solubility,emulsifying properties and foaming activity than that of the SPI-DX microwave group,while the SPI-DX microwave group significantly improved the foaming stability and surface hydrophobicity.The structure of SPI were achieved by fluorescence spectroscopy,gel electrophoresis,fourier transform infrared spectroscopy,raman spectroscopy and scanning electron microscopy.Fluorescencespectroscopy showed that the maximum absorption intensity of the two SPI-DX conjugates were increased.In SDS--PAGE gel electrophoresis,there were large molecular weight aggregates.The result of fourier transform infrared spectroscopy and raman spectroscopy indicated that the secondary structure content of the two SPI-DX conjugates were changed from irregular curling to beta-folding.The tryptophan residues of side-chain and the ratio of Nexposed: Nburied were determined by Raman spectroscopy,which displayed the tryptophan residues were transferred from the embedded,hydrophobic microenvironment to the exposed forming.And there were more tyrosine exposed to the polar solution microenvironment,leading to increase the surface hydrophobicity.After the saccharification reaction,the g-g-t conformation of disulfide bond in the two SPI-DX conjugates were changed.The structures of the samples observed by scanning electron microscope showed that there were larger grafting molecules with water bath group and microwave group,while the original SPI group had regular particle shape.These results indicated that the SPI and DX had cross-linking in the saccharification reaction.Through the comparative study of water bath and microwave method,The appropriate should be applied to improve the specific properties of protein,which could improve the functional properties of protein to a large extent and promote the application in food field.Meanwhile,the functional and structural properties promoted by saccharification reaction should be closely linked together,which would build a foundation for protein properties to be better applicated.