Purification of proanthocyanidins from nut seeds and study on its bactericidal mechanism against Streptococcus mutans

Abstract Aim The aim of this study was to purify proanthocyanidins from areca nut seeds (P-AN) and to investigate the bactericidal activity and mechanism of the purified products against S. mutans. Methods and Results UPLC-Q-TOF-MS, FT-IR, MADLI-TOF-MS and thiolysis experiment were used for P-AN chemical analysis. Time-kill analysis and glycolytic pH drop were used to evaluate the activity of S. mutans in vitro. Meanwhile, the investigation of the bacteriostatic mechanism included membrane protein, fluidity, permeability and integrity tests. The results showed that P-AN was a kind of proanthocyanidins mainly composed of B-type proanthocyanidin and their polymers. Moreover, MADLI-TOF-MS and thiolysis experiments demonstrated that the degree of polymerization (DP) of P-AN was 13. The time-kill analysis showed that P-AN had strong bactericidal activity against S. mutans. P-AN at MIC concentrations was able to induce S. mutans death, while complete lethality occurred at 2 MIC. Glycolysis test showed that P-AN significantly inhibited S. mutans acid production (p < 0.01). The morphological changes of S. mutans were observed by SEM and TEM experiments, which indicated that P-AN destroyed the cellular structure of S. mutans. At the same time, significant changes were observed in membrane proteins, fluidity, permeability and integrity. Conclusion P-AN can effectively inhibit the activity of S. mutans. P-AN can reduce the erosion of the tooth surface by the acid of S. mutans. P-AN could break the structure of cell membrane protein of S. mutans. P-AN could destroy the integrity of membrane, resulting in the death of S. mutans.