Insights into ultrasound-modified soy protein isolate-inulin hydrogels: Focus on binding mechanisms, stability, and riboflavin controlled-release behavior

The loose structure of natural soy protein isolate (SPI) gels limits their application in food nutrient delivery systems. This study investigated the effects of varying inulin (INU) concentrations combined with ultrasound treatment on the structural characteristics, stability, and riboflavin digestion and release of SPI-based hydrogels. Increasing INU concentration enhanced the textural properties and water-holding capacity (WHC) of the composite gels, converting free water into immobilized water. The addition of 2 % INU with ultrasound treatment (SU-2) markedly improved rheological properties, yielding a smoother, denser microstructure and increasing protein disorder. Molecular docking and molecular dynamics simulations indicated that the SPI-INU gel structure was stabilized primarily through hydrogen bonding and hydrophobic interactions. The modified gels improved riboflavin loading and stability, with SU-2 exhibiting the highest bioaccessibility (85.82 %) and chemical stability (76.01 %). This study contributes to the development of natural protein/polysaccharide gel carriers for targeted slow release of hydrophilic bioactives.