Ultrasonic processing and alkylation were used to modify the protein, improved the emulsifying stability of soybean protein isolate(SPI). The modified product was analyzed by FTIR indicating the alkylation reaction. The effect of ultrasonic power, ultrasonic time, substrate concentration, reducing agent amount, alkylation reaction time on the emulsifying stability of modified soybean protein isolated were studied by single factor experiments. Through the response surface methodology, the optimal process con...