Investigation of the formation mechanism of the oxidized soybean protein/linoleic acid aggregates: Effect of heating treatment on the soybean protein emulsion structure, antioxidant properties and accessibility of vitamin D3.

The aim of this study was to investigate the effects of heating-induced conjugation between soybean protein isolate (SPI) and linoleic acid (LA) on the structural modifications of the protein, the antioxidant activity of the oxidized protein, and the bioaccessibility of vitamin D3. The results revealed that the LA facilitated the formation of oxidized soy protein aggregates, which demonstrated that the protein oxidation degree increased. The simultaneous rheology and fourier transform infrared spectroscopy measurements made an analysis of the structural changes of proteins caused by oxidation, the α-helix decreased and the β-fold increased, indicating that oxidation changed the structure of SPI and increased its flexibility. The confocal laser scanning microscopy revealed that oxidized soybean protein isolate treated at 60 °C (OSPI-60) exhibited minimal particle size with optimal structural characteristics. Following in vitro digestion, the OSPI-60 demonstrated ABTS and DPPH radical scavenging capacities that were 19.18% and 16.61% higher than those of SPI, respectively. Evaluation of the constructed SPI and LA emulsion revealed that the OSPI-60 exhibited superior stability, with the highest in vitro accessibility (90.23%) for the encapsulated vitamin D3. This study provides new insights into developing nutritionally fortified soybean flour matrices and extending their application as a wall material for delivering lipophilic nutrients in powdered foods.