Insight into the binding mechanism between soy protein isolate-oat β-glucan extrudate and quercetin in nanoparticles by multi-spectroscopic techniques

Nanoparticles prepared by soy protein isolate (SPI)-oat β-glucan (OG) extrudates (E-SPI-OG) could encapsulate quercetin and improve its bioaccessibility. This study systematically investigated the binding mechanism between E-SPI-OG and quercetin in nanoparticles using multi-spectroscopic techniques. The results revealed that fluorescence quenching via static type occurred during the interaction between E-SPI-OG and quercetin, accompanied by the occurrence of non-radiative energy transfer (binding distance was 2.99 nm and less than 7 nm). The interaction between E-SPI-OG and quercetin was an endothermic and spontaneous binding process (ΔH > 0 and ΔG < 0) and mainly driven by hydrophobic interactions (ΔH of 4.92 kJ·mol^-1 and ΔS of 121.39 J·mol^-1·K^-1). Tryptophan and tyrosine residues of E-SPI-OG were involved in binding to quercetin, resulting in a larger binding constant (2.07-5.48 × 10⁵ L·mol^-1) and more binding sites (1.15-1.25). Quercetin altered the secondary structure of E-SPI-OG (α-helix content was reduced from 8.9 % to 6.75 %), causing its structure to become loose.