Preparation of soybean 7S/11S proteins-quercetin nanocomplexes through heat treatment: Effects on stability, in vitro digestion and bioactivities of quercetin

In this paper, soybean 7S and 11S protein nanocarriers were constructed through heat treatment (H7S/H11S) to encapsulate and protect quercetin (Que). The incubation temperature and the mass ratio of protein to Que were optimized for the nanocomplexes fabrication, and it was found that the encapsulation efficiency of H7S/H11S-Que nanocomplexes reached 94.59% and 85.77%, respectively, when the temperature was 60 °C and the mass ratio of protein to Que was 40:1. Compared with free Que, the nanocomplexes can significantly improve the stability and antioxidant capacity of Que, reduce its degradation by the digestive system and enhance its inhibitory effect on CT26 cell proliferation. Additionally, the H7S/H11S-Que nanocomplexes also exhibited good inhibitory ability against α-glucosidase/α-amylase. Fluorescence spectral results demonstrated that the spontaneous interaction between Que and H7S/H11S could decrease the intrinsic fluorescence of 7S/11S through static quenching mechanism, and a non-covalent protein-Que complex with a 1:1 binding stoichiometry was formed, primarily involving hydrophobic interactions and hydrogen bonds. Simultaneously, the binding of Que induced significant secondary structural modifications (increasing α-helix and random coil content, while decreasing β-sheet and β-turn content) and reduced the surface hydrophobicity of H7S/H11S. These findings offered a promising new approach for developing soybean protein-based nanocarriers with exceptional encapsulation capability, and also broaden the application of Que in the fields of food and medicine.