Research On Soy Protein Isolate Of Ultrasonic-alkylation Modification And Application On Milk Tea

Because SPI had a high nutritional value and a series of functional characteristic such as emulsibility, solubility and gel property, etc., it was used as a kind of functional material widely in the field of food. The emulsibility was a kind of important functional properties of SPI. The SPI added to food could improve the taste, could help to form oil in water emulsion, could be used as a stabilizer of oil-water emulsion system and prolonged the shelf life of food. But in some of the food system(such as milk tea, ice cream, etc.) its application was restricted due to poor emulsifying stability. In order to solve this problem, this study discussed the effect of the different coexistence in the milk tea system on emulsibility of SPI. It aimed to improve the emulsifying stability of SPI in the milk tea system by means of modification technology, and could widen its application in food processing. The main content and results of the research were described below.In the experiment of researching the effect of the different coexistence of milk tea system on emulsibility of SPI, the effect of casein, monostearin, cream, tea polyphenol, saccharides, salts, milk powder and black tea powder on emulsibility of SPI were studied by single factor experiment. The influence law of interaction of coexistence of milk tea system and SPI on emulsibility was explored by measuring the zeta potential and particle size of emulsion. The results showed that because of the different nature of various coexistence, with the increase of adding amount of coexistence, the influence on the emulsibility of SPI has a lot of difference. The emulsion formed by a mix of coexistence and SPI has a smaller zeta potential absolute value, the droplets were more likely to gather, the average particle size of emulsion was the larger, and the emulsibility of SPI was more worse.In the experiment of using ultrasonic technology to improve the emulsifying stability of SPI, the effect of substrate concentration, ultrasonic power and ultrasonic time on the emulsibility was studied by single factor experiment, and the best modification condition was optimized by response surface: the substrate concentration 1.12%, ultrasonic power 498.05 W and ultrasonic time 6.14 min. The emulsifying stability(OD500) of SPI made by ultrasonic under this condition was 31.27 min, increased by 57% than the unmodified SPI.In the experiment of using alkylation reaction to improve the emulsifying stability of SPI, the effect of substrate concentration, reducing agent amount and reaction time on the emulsibility was studied by single factor experiment, and the best modification condition was optimized by response surface: the substrate concentration 1.02%, reducing agent amount 0.16% and reaction time 62.19 min. The emulsifying stability(OD500) of SPI was made by alkylation under this condition was 50.93 min, increased by 150% than the unmodified SPI.In the experiment of using ultrasonic-alkylation compound method to improve the emulsifying stability of SPI, the effect of ultrasonic power, ultrasonic time, substrate concentration, reducing agent amount and reaction time on the emulsibility was studied by single factor experiment, and the best modification condition was optimized by response surface: ultrasonic power 468.61 W, ultrasonic time 6.10 min, the substrate concentration 1% and reducing agent amount 0.16%. The emulsifying stability(OD500) of SPI was made by ultrasonic-alkylation under this condition was 63.27 min, increase by 210% than the unmodified SPI.The effect of the ultrasonic-alkylation compound modification on the emulsifying stability of SPI was the most obvious among the comparison of three kinds of modified method.The structure of SPI were analyzed by infrared spectroscopy and scanning electron microscopy before and after ultrasonic-alkylation modification. The result of infrared spectrum analysis showed that stretching vibration was happened by the aromatic ring C-H, aldehyde group C-H and aromatic amine C-N. There was a new group in the-NH2. The alkylation reaction was happened by amino of SPI and carbonyl of benzaldehyde. The analysis results of scanning electron microscopy showed that the ultrasonic-alkylation modification methods made the structure of SPI stretch. The internal embedded group was exposed.The safety analysis of ultrasonic-alkylation modified SPI was carried out. The results showed that the residual quantity of cyano sodium borohydride and benzaldehyde in the SPI by means of ultrasonic-alkylation method were in accord with national standard.The experiment results of milk tea application showed that the orthogonal optimization experiment could determine the adding quantity of whole milk powder 2%, the adding quantity of black tea powder 0.2% and the adding quantity of sucrose 2%. And the stability and sensory were analyzed by milk tea added SPI of ultrasonic-alkylation. That determined the best addition amount of ultrasonic-alkylation modified SPI were 0.2%. Compared with the milk tea of adding unmodified SPI, the milk tea of adding modified SPI has a smaller centrifugal sedimentation rate, grease exhalation rate, smaller viscosity, better stable effect and higher the comprehensive score of sensory evaluation. The stability of milk tea of adding modified SPI reached standard of milk tea in maket. Applying SPI of ultrasonic-alkylation to milk tea improved the stability, nutritional value, sensory score of milk tea effectively and met the needs of the consumers.