Effect Of Papain Hydrolysis And Phosphorylation On Solubility Of Soybean Protein Isolated

Soybean protein isolated(SPI) has high protein content,no cholesterol,and has a variety of features such as gelation,emulsification,water holding capacity,oil holding capacity to be widely used in food processing areas.Now domestic production of SPI homogeneity.The most primary functionality was gelation,mainly used in meat products such as ham.Functional protein varieties that has high solubility,emulsification etc and functional stabilities were poor.Especially SPI of high solubility under the condition of acid were not seen.The SPI were greatly limited to be used widely in food industry.This study were about poor SPI solubility under acidic condition,aimed at improving SPI solubility under acidic conditions through the modiflcation.The theoretical support was provided for the application of SPI in acidic beverages.The main research contents and results were as follows:1-Selection of modification method of SPI.Throug comparing the solubility of SPI in the isoelectric point under the modification method of enzymatic modification,phosphorylated modification,enzymolysis-phosphoryation compound modification,phosphorylation-enzymolysis compound modification,determined the best modification methods.The results showed that the solubility of enzymolysis--phosphoryation compound modification SPI in the isoelectric point was greater than the enzymolysis modified SPI,phosphorylation modified SPI and enzymolysis-phosphoryation compound modified SPI.So the method of enzymolysis-phosphorylation compound modified SPI was chosed.2.Technology optimization of SPI hydrolyzed by papainThe effect of the concentration of SPI, reaction temperature, reaction pH and reaction time on NSI valued and DH value of SPI were researched through single factor experiment. The enzymolysis conditons were optimized using the orthogonal test. NSI value was the evaluation index. The results indicated that the effect order of four factors on the NSI value was as follows: addition of enzyme, pH, reaction temperature, reaction time. The results showed the suitable conditions were:addition of enzyme was3500U/g、pH was7.5, reaction time was120min,reaction temperature was60℃, Under the optimum conditions, the NSI value was86.2%,DH value was attained7.89%,enzymolysis SPI was without bitter taste.3.The determination of optimum phosphoryation condition of SPI hydrolysateThe effect of the concentration of STP, reaction temperature, reaction pH and reaction time to NSI valued and phosphorus content of SPI hydrolysate were researched through single factor experiment. NSI value was the evaluation index. The optimal parameters of phosphoryation SPI hydrolysate were got using response surface methodology. The results indicated that the effect order of four factors on the NSI value was as follows:reaction temperature, reaction time, concentration of STP, pH.The suitable conditions were:pH was8.45, reaction temperature was39.83℃, concentration of STP was6.87%,reaction time was3.24h, Under the optimum conditions, the NSI value was63.88%, phosphorus content was9.80mg/g.4. Analysis of functional properties and structural characterization of compound modified SPIAfter enzymolysis-phosphoryation compound modification, the solubility improveds significantly between pH2and9. Isoelectric point moved from around4.5to3.5. SPI was hydrolyzed by papain and phosphroylated with sodium tripoly phosphate. The nitrogen solubility index of SPI at pH4.5was improved from2.98%to63.14%。The emulsification of compound modified SPI was lower than unmodified SPI,but it was higner than enzymolysis SPI.The oil-holding capacity of SPI was increased, water-holding capacity was reduced. According to the analysis of the Fourier Transform Infrared Spectroscopy, the SPI molecule was grafted with theodium tripoly polyphosphate by the covalent bond,phosphate was mainly attached to the nitrogen atom. The surface structure was different between SPI and modificed SPI by Scanning Electron Microscope. The structure of SPI was flat surface and firm, but structure of modified SPIwas porous and loose. Disulfide bond of modificed SPI were reduced, free thiol were increased.This study solved the poor solubility of SPI under the acid condition by enzymolysis-phosphorylation compound modification,optimized the modification conditions and provided the theoretical basis and technical support for functional SPI production.