Effects Of Na₂SO₃ And MTGase On Functional Properties And Structure Of Soybean 7S Globulin

Soybean 7S globulin was extracted from the defatted soybean meals,Soybean 7S globulin was crosslinked by MTGase,and under synergistic effect of Na₂SO₃.The gel and emulsifying properties of soybean 7S globulin were studied,and the optimal MTGase crosslinking conditions were determined.Following that changes of surface hydrophobicity,free sulfhydryl and thermal specificity before and after crosslinking were studied,so as to better solve the problem.The relationship between gel properties,emulsifying properties and protein physicochemical properties was explained,and the mechanism of improving the functional properties of soybean protein by different cross-linking treatments was discussed.The main contents and results of research are as follows:?1?Determine the optimal cross-linking conditions for the gel characteristics and emulsifying properties of soybean 7S globulin with MTGase treatment and synergy of Na₂SO₃.Firstly,Soybean 7S globulin was treated with Na₂SO₃ at a concentration of 900 mg/L for 0.5 h.On this basis,the optimal conditions of MTGase crosslinking Soybean 7S globulin were determined by single factor and response surface optimization experiments.The optimum technological parameters were determined by response surface analysis.The optimum parameters were as follows:MTGase addition 20 U/g,reaction pH 6,reaction temperature50?,reaction time 1 h,the gel strength of soybean globulin was the highest,on these conditions,the gel strength value was 120.97 g.MTGase addition 20 U/g,reaction pH 7,reaction temperature 55?,reaction time 1 h,the emulsification of Soybean 7S globulin is the highest,on these conditions,the emulsification value is 86.92 m²/g,which is consistent with the predicted value.It shows that it is feasible to optimize the treatment conditions of Soybean7S globulin with Na₂SO₃ and MTGase by response surface,and the optimized process conditions are reliable.?2?To explore the relationship between the changes of gel properties of soybean 7S globulin and its structure through MTGase cross-linking treatment and use Na₂SO₃ to collaborate with MTGase The gel strength,rheological properties,surface hydrophobicity and thermal properties of soybean 7S globulin gel samples under the optimal cross-linking conditions were determined.The results showed that compared with soybean 7S globulin,the one prepared by Na₂SO₃ and MTGase cross-linking,formed a soft gel.The gel strength and gel water holding capacity increased.The elastic modulus and viscosity modulus of gel increased,the elastic modulus is higher than viscosity modulus of gel which were in sharp contrast with those of untreated soy 7S globulin gel curve.After treatment,the surface hydrophobicity of soybean 7S globulin was significantly reduced,the content of free thiol was increased,and the protein was increased from 10.17 mol/g to 19.59 mol/g;DSC was used to determine the thermal stability of the protein.It was found that the denaturation temperature of the soy protein globulin gel treated by treatment increased by 20.72?and the denaturation enthalpy increased by 108.04 J/g compared with the untreated soybean 7S globulin.soybean 7S globulin:the content of?-helix,?-fold,?-corner and irregular crimp in the secondary structure of Soybean 7S globulin treated by MTGase increased.Compared with the untreated 7S globulin,the content of?-helix,?-fold,?-corner and irregular crimp decreased in the samples treated by Na₂SO₃ and MTGase.The micro structure of the protein is closely heterogeneous from the surface structure.There is a typical?-with soybean globulin torn lamellar accumulation structure.The surface structure is uniform and rough and the protein cluster is large.The interior has small cavities with holes around,fine and uniform The MTGase cross-linked soy7S globulin with Na₂SO₃ had similar changes with the MTGase treated 7S samples,but the changes were not obvious compared with the 7S samples treated with the synergistic treatment.The results showed that the relationship between the changes of gel properties and the physicochemical properties of soybean 7S globulin was more worthy of discussion.?3?To explore the relationship between emulsification and structure of Soybean 7S globulin treated by MTGase and Na₂SO₃ combined with MTGase.The emulsification characteristics,average particle size,Zeta potential and surface hydrophobicity of the samples were determined under the optimal conditions.The results showed that the emulsification characteristics of soybean 7S globulin after MTGase cross-linking and Na₂SO₃ with MTGase cross-linking were significantly improved compared with that of Soybean 7S globulin.The emulsification value increased by 257.40%compared with the untreated sample,and increased by 172.97%compared with the MTGase treated sample.The surface hydrophobicity of Soybean 7S globulin increased by 23.88%and 61.89%respectively after two kinds of cross-linking treatment,and the free sulfhydryl content of Soybean 7S globulin increased by 12.35?mol/g after the cross-linking treatment of Na₂SO₃ and MTGase;the average particle size of protein increased and the Zeta potential of Soybean 7S globulin treated by MTGase crosslinking and synergistic treatment decreased due to the electrostatic effect of protein molecules;compared with the microstructure of Soybean 7S globulin treated by MTGase,the surface structure of sample 7S began to become rough.The number of torn lamellar stacking structure increased and the surface viscosity of 7S globulin treated by synergistic treatment also increased.In addition,there are small cavities inside and irregular floccules on the surface.