Structural modification of thinned-young apple polyphenols-zinc complex and its antibacterial activity against halitosis-related bacteria.

YAP-Zn, CGA-Zn and phlorizin-Zn complexes were prepared by thinned-young apple polyphenols (YAP), chlorogenic acid (CGA), and phlorizin with zinc chloride. Scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), and thermogravimetric analysis (TGA) were employed to characterize the structures of the three ligands and their respective complexes. The results showed that zinc ions were complexed with phenolic hydroxyl and carboxyl groups of YAP at a ratio of 1:3, and the thermal stability of the complexes were improved compared to the YAP. YAP and YAP-Zn have minimum inhibitory concentration against P. gingivalis (8.00 mg/mL and 2.00 mg/mL), with viability of 47.89 % and 36.94 %, respectively. Scanning electron microscopy (SEM) and flow cytometer observation revealed that YAP-Zn could cause more significant changes of the P. gingivalis cells and induce cell death, compared with YAP treatment. With the increase of YAP and YAP-Zn concentrations, the permeability of the outer membranes (OM) and inner membranes (IM) of P. gingivalis dramatically increased and the membrane potential (MP) decreased, and the YAP-Zn treatment was even more. These results demonstrated that YAP-Zn exhibited stronger antibacterial activity against P. gingivalis compared to the YAP. It is speculated that the complexation of YAP with zinc ions enhanced the thermal stability and antibacterial activity of YAP. YAP-Zn complexes are expected to use an antibacterial agents for halitosis-related bacteria in dental care.