Ultrasound-Assisted Soaking Facilitates Purine Dissolution from Soybean Powder: Development and Preliminary Application of Low-Purine Soybean Powder

People suffering from gout and hyperuricemia have limited consumption of soy products because of their high purine content, even though soybean is a nutrient-rich crop. This study developed a combined purine reduction process: ultrasonic-assisted soaking to promote purine dissolution and isoelectric point precipitation to separate purines with minimal protein loss. A high-performance liquid chromatography (HPLC) method for rapid purine determination was first established (R2 > 0.9999, RSD < 0.23%), thereby providing technical support for process optimization. Using soybean powder as the raw material, optimal ultrasonic conditions (58 °C, 250 W, 58 min) were identified, achieving a purine removal rate of 61.15% with a protein recovery of 94.23%. Scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy analyses revealed that ultrasonic treatment altered the microstructure of the soybean powder, thereby facilitating purine dissolution. Low-purine soymilk prepared from the resulting soybean powder exhibited a unique flavor, with enhanced electronic nose response signals of its flavor compounds. This process effectively reduces purine content while preserving soy protein and flavor, offering a feasible technical solution for the development and industrial application of low-purine soy products. However, challenges remain in process scale-up and in optimizing the balance between purine removal and nutrient retention.