Abstract: To clarify the formation mechanism of soybean protein nanofibrils and broaden the industrial application of iron fortifiers, nanofibrils were prepared by heating soy protein isolate (SPI) for five hours under acidic conditions in the present study. Changes in protein structure before and after fibrillation were systematically investigated. Furthermore, iron nanoparticles (Fe NPs) were prepared and the stabilizing effect of SPI nanofibrils on them was evaluated. The results showed that during the formation of SPI nanofibrils, a considerable amount of β-sheet structure was produced and combined with thioflavin T, increasing the fluorescence intensity. In addition, the degradation of 7S fraction was observed at the early stage, being conducive to the formation of fibril nucleation, and then 11S was gradually hydrolyzed, promoting fibril growth. Meanwhile, a large number of small peptides were produced, improving the reducing power of the hydrolysate. SPI nanofibrils were used to deliver Fe NPs. It was found that Fe NPs and SPI nanofibrils could form in situ a complex with good colloid stability, existing as Fe (II) and having less influence on the color and stability of emulsions compared with ferrous sulfate and ferric chloride. The results of the present study should guide the construction of a new plant-based iron delivery system.

Key words: soy protein isolate; nanofibrils; iron nanoparticles; nanocomposite; stabilization