Study On Enhancing The Surfacing Activity Of Soy Protein By Cleaving Disulfide Bond And Glouse Grafting

Due to the presence of disulfide bonds,most of the hydrophobic amino acids areentrapped inside the molecule,which is resulting in non-uniform distribution of hydrophilic/lipophilic groups,so the natural soy protein isolate has a lower surface activity.In this paper,peracetic acid is used to control the disulfide bond in the protein,so that the hydrophobic groups inside the molecule are exposed to the surface of the molecule,which changes the distribution of hydrophilic and hydrophobic groups on the surface of the protein molecule.The results are as follows:1.The nitrogen content of the soy protein isolate was determined by the Kjeldahl method and the soluble protein content was determined by the biuret method.The soy protein isolate was oxidized using different concentrations of peracetic acid.The results show that:as the concentration of peroxyacetic acid increases,the degree of disulfide bond cleavage increases sequentially.When the disulphide bond breaking rate was 46%,the emulsifying property and foaming property were the best,in which the emulsifying property and emulsifying stability were increased by 58.11%and41.74%,and the foaming property and foaming stability were improved by 120%.43%.Under these conditions,the?_CMCwas53.12 m N/m and the CMC was 0.15 g/L with surface active.The HLB value is 9,which is relative stronger lipophilicity.Fluorescence and Chromatography showed that the disulphide bond was broken and the internal hydrophobic groups were exposed,which is leading the?-helix decreased,the?-sheet increased,the structure became loose,and the hydrophobicity increased.Particle size shows that the particle size becomes smaller and the homogeneity is increased due to oxidation.SDS-PAGE confirmed that the decomposition of 11S basic subunits and the molecular weight decreased,and 7S did not change significantly.2.On the basis of controlled cleaving disulfide bonds by peracetic acid,glucose molecules were introduced.The compound products of soy protein isolate and glucose were prepared by dry grafting onto their composites,to studied their surface activities and structural changes.With the degree of grafting?DG?and browning as indexes,the effects of reaction temperature,ratio of protein and sugar,and reaction time on the grafting reaction were studied.Single factor experiments were conducted and the conditions for the reaction were finally established.The results show that:after adding glucose molecules,the amino group content in the solution changes significantly,and breaking the disulfide bond can increase the efficiency of the glycosylation reaction.Emulsifying and emulsifying foaming increased by 128%and 51.91%.Foaming and foaming stability increased by 200%and 72.5%.The surface tension increased first and then decreased.The results of fluorescence spectra showed that the fluorescence intensity of the composite products decreased with the increase of the disulfide bond breaking degree.The particle size profile shows that the average particle size increases slightly after addition of glucose,and there is a peak at low nanometers.The circular dichroism spectra showed that with the progress of the reaction,?-sheets gradually increased,the content of?-helix and random coil structure gradually decreased,and?-turn angle did not change significantly.SDS-PAGE showed that the11S subunit and the 7S subunit of the product were generated by graft modification.3.On the basis of using peracetic acid to cleave disulfide bonds,dextran molecules were added to prepare the composite product by wet grafting.The results show that:with the increase of the disulfide bond breaking degree,the grafting degree increased obviously,and the degree of browning and the grafting degree had the same tendency.Emulsifying and emulsifying stability increased by 107.56%and 175%compared with soybean protein isolate.Foaming and foaming stability increased by 83.63%and105%,respectively.The surface tension first decreases and then rises.The particle size distribution was observed,and the average particle size of the composite samples increased,which is indicating new substances were generated.SDS-PAGE further confirmed that the 7S subunit disappeared first during the glycosylation process.After the disulfide bond was broken by peroxyacetic acid,the glycosylation reaction between the 11S acid subunit and glucan was accelerated.