Effect Of Different Modification Methods On SPI Structure And Functional Properties And Emulsion Oxidation Stability

Soy protein has a wide range of applications in the food industry because of its good functional properties(such as emulsifying properties,solubility,etc.),however,the structural effects of food processing on soy protein and thus the oxidation stability of soy protein oil-in-water emulsions.Change,relative research is less or not systematic.Therefore,in this paper,soy protein isolate was used as the research object,and the effects of high temperature and damp heat,pH migration and high pressure microjet on its structural and functional properties and emulsion oxidation stability were studied.The main findings are as follows:The effects of high temperature wet heat treatment(blank,70°C,90°C,120°C,150°C,170°C and 200°C)on the structural properties of soy protein isolate and the oxidation stability of the emulsion were studied.The results showed that the surface hydrophobicity of untreated soy protein isolate was 96.74.When the treatment temperature was in the range of 70-90°C,the hydrophobicity of soy protein isolate was positively correlated with the heating temperature and reached at 90°C.At the maximum,as the heating temperature rises further,the surface hydrophobicity of SPI shows a downward trend.From the fluorescence spectrum analysis,the fluorescence intensity of the soy protein isolate soy protein isolate after temperature treatment is generally lower than that of the treated protein samples.The maximum absorption wavelength of the protein solution increased continuously,resulting in a certain degree of red shift,which indicated that the tertiary structure of the protein molecule changed;SDS-PAGE analysis showed that the soy protein isolate subunit component after high temperature wet heat treatment did not produce significant The results of infrared spectroscopy indicated that the high temperature wet heat treatment changed the secondary structure of soy protein isolate,the ?-sheet content decreased,and the ?-helix content increased.At 90°C,the solubility of the protein was the highest;as the temperature increased,the protein emulsified.The first increase and then decrease,the emulsion stability gradually increases;the particle size distribution of the protein emulsion shows that As the heat treatment temperature increases,the particle size of the emulsion increases first and then decreases,and at a temperature of 170°C,the decrease is significant,and the absolute value of the soy protein isolate is smaller and smaller;according to the formation of primary oxidation products and secondary oxidation products of the emulsion It can be seen that high temperature promotes the oxidation of oils and fats,and also changes the protein structure on the surface of the oil,and the secondary oxidation rate of the emulsion is similar to the primary oxidation rate.Secondly,the effects of pH on the functional properties of soy protein isolate and the oxidation stability of the emulsion were studied.Acid-alkaline treatment increased the surface hydrophobicity of soy protein isolate and increased the surface hydrophobicity after alkaline treatment.The infrared spectrum showed the content of each component in the secondary structure of protein after different pH treatment.The change is more obvious.Under acidic conditions,the random coil structure and the ?-helical structure accounted for more,the ?-fold structure and the ?-turn structure occupied less,and the occupancy of the protein ?-helical structure and the pH value under alkaline conditions were treated.In a positive correlation,the ?-fold structure occupancy was negatively correlated with the pH value,and the random coil structure content decreased slightly.The endogenous fluorescence results showed that the maximum absorption wavelength of the soy protein isolate after pH treatment increased correspondingly.The absorption wavelength is red-shifted;different pH treatments can improve the emulsification and emulsion stability of soy protein isolate;the soy protein isolate is treated under alkaline conditions,and the solubility is significantly increased;the emulsion particle size distribution shows that at pH 1 and At 12 o'clock,the effect on the particle size distribution of the emulsion was significant;the pH of the stable soy protein isolate emulsion was positive in the range of 1-3,the pH was in the range of 10-12,and the ?-potential of the emulsion The absolute value of the absolute value is negative.When the pH is away from the isoelectric point,the absolute value of the?-potential becomes smaller.Under acidic conditions,the primary oxidation rate of the emulsion is faster,and the acidity is higher.The faster the rate of oxidation,the tendency of secondary oxidation product formation is similar to that of the primary oxidation product hydroperoxide.Under alkaline conditions,with the increase of pH value,the primary oxidation rate of emulsion oil decreased,and the trend of secondary oxidation product and primary oxidation product formation rate was significantly different.Finally,high-pressure microjets were used to treat soy protein isolates to study the changes in their structural and functional properties and their effects on emulsion oxidation stability.The average particle size of soy protein isolate treated by high pressure microjet was significantly reduced;the change of endogenous fluorescence spectrum of tryptophan was mainly manifested by the increase of maximum absorption wavelength(red shift)and decrease of fluorescence intensity;surface hydrophobicity of protein It has a positive correlation with the pressure of treatment;when the pressure is 35 MPa,its emulsifiability is the largest,which is 76.56 m2/g.Excessive pressure treatment causes the emulsification to decrease to some extent;when the pressure reaches 95 MPa,the solubility The maximum is 76%;the particle size of the emulsion of the SPI sample treated by microfluidization increases;when the homogenization pressure increases to 155 MPa,the absolute value of the potential of the SPI emulsion increases significantly;the pressure is 65 MPa.Under the conditions,the primary oxidation rate of emulsion oil is the fastest,and the secondary oxidation rate is different from the primary oxidation rate.The primary oxidation rate of emulsion at 125,155 MPa is lower than that of untreated emulsion.