Effects of fabrication of conjugates between different polyphenols and bovine bone proteins on their structural and functional properties

Covalent complexes of bovine bone proteins (BBP) with four polyphenols (chlorogenic acid (CA), quercetin (Q), rutin (R), epigallocatechin gallate (EGCG)) with were prepared to increase the high-value utilization degree of bovine bone. The differences in coupling effect and structural and functional properties between the conjugates were also investigated. The results showed that EGCG-BBP had the highest polyphenolic equivalent at 88.05 mg/g protein and the lowest sulfhydryl group content. EGCG-BBP also had the best covalent effect. The SDS-PAGE and fluorescence spectra results revealed that the molecular weight of the conjugates increased significantly as different polyphenols conjugated with the aromatic amino acids in BBP, resulting in significant changes in the structure of EGCG-BBP. Fourier Transform infrared spectroscopy (FTIR) analysis demonstrated that the amide I band of conjugates was slightly shifted, indicating that the polyphenols were covalently bonded with BBP. Based on the results of this study and well-established mechanisms, it could be speculated that the best covalent effect of EGCG may be not only due to the eight phenolic hydroxyl groups but also to its two benzene rings, which are greatly increased in its reaction site. In terms of functional characteristics, EGCG-BBP had the highest 1-diphenyl-2-picryl-hydrazyl radical (DPPH·) scavenging capacity, while Q-BBP had the best solubility. Thus, this study provides a theoretical basis for different polyphenols' structural and functional effects on covalently modified proteins.