The Study On Properties Of Soybean Protein Isolate-saccharide Grafts Synthesized By Microwave Under Solvent-free Condition

Soybean protein was rich in natural resources, and with low prices. There aremang domestic enterprise with production of soybean protein products, but assoybean protein serious denaturation in the process of production, resulting in poorfunctional properties of soypean protein, greatly limit its widespread application inthe food industry. The grafting reaction protein with sugar can be effectively improvethe functional properties of protein. Based on soybean protein isolated (SPI), lactoseas the main raw material, using microwave solvent-free glycosylation package knotand microwave solvent-free glycosylation reaction synthesis of two kinds of SPI-sugar (SPI-L-Alumina, SPI-L) grafting, and graft material physical and chemicalproperties, structure, rheological property, sensitization and harmful productsgenerated has carried on the systematic study, to obtain a new, fast and effectiveprotein modification methods, then obtained a theoretical basis and method guidancefor the industrial production of protein-sugar grafting products.1. Under the full power of microwave treatment,, the free amino content of SPIgradually decreased with the extension time of microwave; The color of the samplesget deeper, color difference gradually increased; The solubility and emulsificationwere increased and then reduced; Thermal stability slightly declined and enthalpyvalue decreased, which showd that intensity of grafted protein reduced. The physicalproperties variations of SPI-L-Alumina and SPI-L have the same trend, but theglycosylation of SPI-L which joined the acidic Alumina showed a lower reaction ratethan the SPI reacted with lactose alone.2. The Amino acid analysis showed that the contents of lysine and arginine weresignificantly reduced; The SDS-PAGE analysis showed that the protein pattern of SPI–lactose changed. When the microwave heating time was shorter (0,30s),electrophoretic bands was not obvious changed. With the extension of microwavetime, the bands of SPI-sugar grafting shifting up, indicating that molecular weight ofprotein increased; IR spectra showed that after the covalent binding protein with sugar, hydroxy increase of the protein molecules, and this will result in infraredspectra in3700~3200cm-1with a broad peak and emerge a new absorption between1260~1000cm-1; Circular Dichroism spectrum showed that the SPI-L graftingcontent compared with the untreated SPI, alpha helix, beta folding and random curlup, SPI-L-Alumina grafting content compared with the untreated SPI, beta foldingand random curl content does not significantly increased and alpha helix; Endogenousfluorescence analysis showed that the SPI were treated with microwave glycosylationafter90s, the largest fluorescence wavelength blue shift from344.2to340nm, therelative fluorescence intensity increased from306.5to934.2, SPI were treated withmicrowave glycosylation after150s, the largest fluorescence wavelength redshiftfrom344.2to344.2nm, the relative fluorescence intensity is reduced from306.5to306.5; Adding alumina carrier after grafting with the increase of microwave time,maximum fluorescence wavelength blue shift, the relative fluorescence intensitygradually increased. With the extension of microwave time, two kinds of SPI-sugargrafted surface hydrophobicity were drop rapidly.3G’ and G " of untreated graft solution and SPI both increased with increasingfrequency, the viscoelastic of samples were enhanced, the tanδ of SPI-graft sugar washiger than the untreated SPI solution; In the thermal cycling process, the solution ofSPI as G ’ had no significant change in the warming and constant temperature stage,but significantly increased during the cooling stage, and the G ’ of graft samples in theheat treatment stage did not change significantly with temperature; Flow curveanalysis showed pseudoplastic behavior of the samples in the whole graft shear raterange than untreated SPI. The low range (0.01~0.1s-1) showing the nature propertiesof Newtonian fluid, but in the high shear rate range also proved the pseudoplasticbehavior. Compared with untreated SPI, the rheological properties of the grafts indexsignificantly decreased, SPI-fluid type described saccharide graft increasing deviationfrom Newtonian fluid solution; ESEM analysis showed that untreated SPI sphericalsurface is uneven with a certain aggregation., SPI aggregation spherical structuredecreased after saccharification treatment, increasing the rod structure, continued toincrease with time of microwave crosslinked chain structure occurs gradually form anetwork structure. 4. The antigen activity of grafting products compared with the untreated SPIsignificantly decreased, after the introduction of sugar molecules in SPI, under thecondition of microwave glycosylation reaction, the reaction can effectively modifythe epitope of sensitization protein, thus generated SPI-sugar grafted objectsallergenic significantly reduced; After microwave treatment, and there is fewformation of acrylamide and HMF in glycosylation SPI products.