The Effects Of Environmental Factors And Glycation On The Oil/water Interfacial Properties Of 7S And Investigations Of Emulsification Mechanisim

Soybean is one of the important economic crops in China,containing about 40%soybean proteins.Soybean proteins are characterized by their large production scale,low production cost,and high emulsifying ability,making them a promising raw material for developing novel emulsifiers.?-Conglycinin(7S)is one of the main components of soybean proteins and it plays a key role in the emulsifying properties of soybean proteins.Studies have shown that the emulsifying performance of soybean proteins depends on their interfacial properties induced by conformation changes.However,it was not clear how these factors affected the emulsifying properties of 7S by regulating their interfacial adsorption behavior.Moreover,the related structure-function relationships were needed to be further investigated.Thus,the effects of environmental factors and glycation treatment on the interfacial properties and emulsifying properties of 7S were investigated.The main results of this work are as follows:1.The effects of protein concentrations,pH values,and Na Cl concentrations on the interfacial adsorption behavior and emulsifying properties of 7S were investigated.(1)when the protein concentration was increased from 0.5 mg/m L to 10 mg/m L,the interfacial pressure of 7S was increased from 10 m N/m to 14 m N/m,and the dilatational viscoelastic modulus was increased from 35 m N/m to 50 m N/m at the oil/water interfacial.Moreover,the particle sizes of emulsions stabilized by 7S were reduced to 0.9 ?m.All these results indicated that the interfacial properties and emulsifying efficiency of 7S exhibited a dramatic dependence on the increase in concentrations.(2)7S at p H 3 and 8 exhibited small average diameters,high Zeta potentials,and high solubility.It positively affected the interfacial adsorption kinetics of 7S and resulted in the formation of viscoelastic layers at the oil/water interfaces,therefore improving emulsifying efficiency and decreasing the emulsion flocculation.(3)When Na Cl concentrations were increased from 0 mmol/L to400 mmol/L,the interfacial pressure of 7S was increased from 10 m N/m to 14 m N/m,and the dilatational viscoelastic modulus was decreased from 50 m N/m to 25 m N/m at the oil/water interfacial.Moreover,the particle sizes of emulsions stabilized by 7S were increased from 0.9 ?m to 2.0 ?m.All these results indicated that Na Cl concentrations had a negative effect on emulsifying efficiency.2.The effects of pH-shift treatment on the interfacial adsorption behavior and emulsifying properties of 7S were investigated.(1)The alkaline p H-shifted treatment did not change the average diameters and Zeta potentials but increased solubility of 7S.However,acidic p H-shifted treatment increased the average diameters(>1000nm)and decreased the Zeta potentials of 7S.The acidic and alkaline p H-shifted treatment increased the hydrophobicity and led to the maximum wavelength of a 4 nm red-shift.Moreover,p Hshifted treatment insignificantly decreased the ?-helix content and increased the ?-sheet content.All these results indicate that p H-shifted treatment significantly changed the conformational state of 7S to form a looser tertiary structure but did not significantly affect the secondary structure.(2)The alkaline p H-shifted treatment improved the interfacial adsorption kinetics of 7S at the oil/water.Still,the acidic and alkaline p H-shifted treatment noticeably decreased the interfacial viscoelastic modulus of 7S to 20 m N/m-30 m N/m.(3)The alkaline p H-shifted treatment improved the emulsification efficiency of 7S,and the emulsions showed stability against heat treatment,but the acidic p H-shifted treatment did not exhibit the same effects.3.The effects of electrostatic interactions with pectin(PC)on the interfacial adsorption behavior and emulsifying properties of 7S were investigated.(1)The interfacial pressure values of 7S/PC mixture at p H 6-7 were larger than that of other p H values,and the viscoelasticity modulus of the interfacial adsorption layers formed by 7S/PC mixture at p H2-3 was significantly larger than that at p H 4-7.These results indicated that the compositions and structures of these adsorption layers formed by mixtures were different due to the influence of p H values.When p H values were decreased from 7 to 2,the particle sizes of emulsions stabilized by 7S/PC mixtures decreased first and then increased.Emulsions stabilized by 7S/PC mixture at p H 4-5 had the smallest particle sizes and exhibited storage stability.It indicated that the electrostatic interactions with pectin improved the emulsifying performance 7S at p H near the isoelectric point.However,due to the competitive adsorption of the pectin,the particle sizes and the degree of flocculation of emulsions stabilized by 7S/PC mixtures at p H 3 were the largest,leading to the phase separation after storage.4.The effects of glycation with D-galactose on the interfacial adsorption behavior and emulsifying properties of 7S were investigated.(1)The glycation degree was increased from 21% to 48% within the reaction time from 12 h to 48 h.As the glycation degree was increased,the average diameters of 7S were increased from 93 nm to 179 nm and Zeta potentials were increased from-19 m V to-32 m V.(2)The glycation led to a red shift of the maximum wavelength for 7-13 nm and significantly increased the hydrophobicity of 7S.Moreover,As the glycation degree was increased,the ?-helix and ?-turn contents were decreased and the ?-sheet and random coil contents were increased.All these results indicated that the tertiary structures of 7S were unfolded,leading to the exposed hydrophobic groups buried inside the structure before,and the second structure also was changed from an ordered one to a disordered one.(3)The glycation treatment promoted the diffusion and conformational unfolding of 7S at the oil/water interfaces,therefore increasing the interfacial pressure to 25 m N/m-30 m N/m.The interactions between proteinprotein and protein-interface were also improved during the successive expansion and compression,which is beneficial for forming the viscoelastic networks and increasing the resistance of these networks to large deformation.(4)The glycosylation significantly improved the emulsification performance of 7S and emulsion stability.Compared to the native 7S,the lower concentrations of glycated 7S were required for preparing for the high internal phase emulsions with self-supportive structures.