Interaction mechanism of flavonoids and Tartary buckwheat bran protein: A fluorescence spectroscopic and 3D-QSAR study

Tartary buckwheat bran protein (TBBP) is a valuable by-product of Tartary buckwheat processing. Current studies have indicated that TBBP is a desirable carrier and protector of flavonoids. However, the quantitative structure-affinity relationship of flavonoids with TBBP still remains to be elucidated. Here, by using the fluorescence spectroscopy method to measure the binding constants of 16 flavonoids with TBBP, we employ a combination of the atom-based three dimensional-quantitative structure-affinity relationships (3D-QSAR) and quantum-chemical calculation to explore the underlying binding mechanisms. We show that flavonoids can cause the intrinsic fluorescence quenching and form non-covalent complexes with TBBP driven by hydrogen bonding and van der Waal forces. The atom-based 3D-QSAR model reveals that the rutoside group at the C-7 position of flavones is favorable to enhance the binding constants of flavonoids with TBBP. Quantum-chemical calculations consistently disclose that the rutoside group can intensify interaction forces of flavonoids, thereby strengthening the binding. This work provides theoretical evidence that TBBP has the potential application to be raw materials for develop functional food, and be the delivery carriers of flavonoids.