Daidzein's extremely low solubility in edible oils limits its application. This study developed a green, solvent-free ultrasound-assisted magnetic stirring strategy to enhance daidzein dissolution in soybean oil. The optimized process increased the dissolved daidzein concentration to a thermodynamic saturation limit of 58.12 mg/kg. While the absolute concentration is modest, the resulting fortified oil exhibited markedly improved storage stability over six months, effectively retarding deterioration in color, acid value, and peroxide value, and better preserving unsaturated fatty acids. Additionally, a simulated French fry model revealed that daidzein retention decreased with increasing temperature and frying duration. This thermal loss was governed by three contributing mechanisms: volatilization, chemical transformation (yielding an unidentified daidzein-derived product), and migration into the food matrix. These findings provide a theoretical foundation for developing daidzein-fortified oils and optimizing thermal processing conditions to retain valuable bioactive components. • An ultrasound-magnetic stirring method enhanced daidzein solubility in soybean oil. • Daidzein fortification significantly improved oil oxidative stability during storage. • Fortified oil better preserved color, acidity, peroxide value, and unsaturated fatty acids. • Thermal loss of daidzein was caused by volatilization, transformation, and migration. • A novel daidzein-fatty acid derivative was identified in heated oil.
Wang et al. (2026) studied this question.