Changes of soy protein under ultra‐high hydraulic pressure

Summary High pressure (<500 MPa) was applied to soy milk and the protein changes were examined. Soy milk remained a liquid within the range of examined pressures, although its viscosity increased when the time of pressurization was less than 10 min. However, the soy milk changed from a liquid to a sol after treatment at 500 MPa for 30 min. the liquid soy milk showed improved emulsifying activity and stability but reduced emulsifying capacity. Sulfhydryl content of this soy milk was increased slightly after anaerobic pressurization. Harder tofu could be made from pressurized soy milk with CaC12 than could be made with unpressurized soy milk. Electrophoresis and isoelectrofocusing revealed that soy proteins were dissociated and some of them coagulated by high pressure. Fluorescence analysis also revealed that soy proteins were modified by high pressure to have larger hydrophobic regions. After pressure treatment, soy milk showed a higher affinity for beany flavour components and saponins which would lead to better use of soy milk in soy foods.