Combined Ultrasound and NaHCO3 Treatment Improves Soymilk Stability and Soybean Flour Quality by Regulating the Structure and Properties of Interfacial Soy Proteins

During soybean processing, insufficient disruption of the soybean cell wall structure limits protein solubilization, thereby reducing the nutritional value and bioavailability of soybean-based products. In this study, ultrasound combined with NaHCO3 was used to induce targeted modification of soybean tissue structure and interfacial protein properties, with the aim of improving protein extraction, soymilk stability, and the digestive properties of spray-dried soybean flour. The results showed that single ultrasound treatment and single alkali treatment could increase the protein extraction rate in soymilk. But compared with the untreated control, the combined treatment increased the protein dissolution rate from 70.04% to 81.12% and decreased the protein residue rate in okara to 19.74%. The treatment also reduced the average particle size from 132.60 µm to 90.61 µm, increased the emulsifying activity index to 35.49 m2/g. Further experiments showed that the combined treatment of ultrasound and alkali increased the content of interface protein and modified protein conformation. These changes contributed to the improvement of storage stability and ionic stability of soymilk. Furthermore, the resulting spray-dried soybean flour exhibited a more uniform particle distribution with reduced interparticle agglomeration, higher solubility (88.37%), and higher in vitro digestibility (89.48%). Overall, the combined treatment enhanced protein solubility and interfacial behavior, thereby improving soymilk stability and soybean flour quality. These findings provide a useful theoretical basis for the development of soybean flour with improved functional and nutritional properties.