Impact of Sugar Content in Ready-to-Drink Green Tea and Exposure Duration on Cariogenic Biofilm pH

Objective: To explore the impact of sugar supplements in ready-to-drink green tea (GT) beverages on the pH levels of cariogenic biofilms over different exposure durations. Material and Methods: Streptococcus mutans biofilms were exposed to GT categorized by sugar content: no-sugar (GT/NS), < 5% sugar (GT/S < 5%), >5% sugar (GT/S > 5%), and 5% sucrose (positive control). Biofilm pH was measured at baseline, 5, 20, 40, and 60 min. The impact of sugar content and exposure times on biofilm pH was assessed using the Generalized Estimating Equation and the least significant difference tests (p < 0.05). Results: The mean biofilm pH at baseline was 4.28 ± 0.01. Sugar content and exposure duration significantly influenced biofilm pH, with a strong interaction effect observed (p < 0.001). Post-hoc analysis revealed that biofilm pH in all GT groups was significantly higher than 5% sucrose at all exposure times, surpassing the critical enamel demineralization pH threshold of 5.5. The biofilm pH in GT/NS and GT/S > 5% significantly increased until 40 min post-exposure, while in GT/S < 5%, the rise stabilized at 20 min. At 60 min, biofilm pH for GT/NS, GT/S < 5%, GT/S > 5%, and 5% sucrose was 6.25 ± 0.11, 5.91 ± 0.18, 5,70 ± 0.21, and 4.83 ± 0.05, respectively. Notably, pH in GT/S > 5% significantly decreased from 40 min (p = 0.006) and was significantly lower than in GT/NS (p = 0.023). Conclusion: The pH of S. mutans biofilm exposed to GT with high sugar concentrations, even over extended periods, is unlikely to drop below the threshold for enamel demineralization. Nevertheless, adding sugar to GT may promote S. mutans growth, as suggested by a significant pH difference between high- and no-sugar GT.