Abstract:The effects of ultrasonic technology on the residual protein content in okara and the protein content in soy whey during soybean protein isolate （SPI） production was investigated. This study investigated the differences in secondary structure between proteins in okara and those in SPI，as well as the impact of ultrasonic treatment during extraction on residual protein content in system effluents （soybean residue and soybean whey）. The results showed that，compared with SPI，the secondary structure of okara protein exhibited an 18.83% lower α-helix content，a 13.40% lower β-sheet content，a 9.40% lower random coil content，and a 41.60% higher β-turn content. After 5 min of ultrasonic treatment，the crude protein content in okara increased by 0.4%. For soy whey derived from ultrasonically treated soymilk，there was no correlation between ultrasonication time and the residual protein content in soybean whey. Ultrasonic treatment of the acid-precipitated slurry resulted in a significantly different protein content in the soy whey compared to untreated samples，with an average value 1.28% lower than that of the untreated blank. The findings indicate that ultrasound treatment of the redissolved slurry is unfavorable for improving protein recovery；ultrasonic treatment of soymilk has no statistically significant effect on the recovery rate of acid-precipitated protein；and ultrasound treatment after acid precipitation reduces protein loss in soy whey.