Promotive effect of cold brew coffee on the maturation of S. mutans biofilms during the post-initiation stage

The widespread use of cold brew coffee and reusable stainless steel drinkware has introduced novel considerations for microbial safety in consumer practices. This study investigates the effects of diluted cold brew coffee (dCBC) on the post-initiation maturation of Streptococcus mutans biofilms on stainless steel surfaces, simulating reusable cup conditions. Despite the known antimicrobial properties of chlorogenic acid (CGA), high-performance liquid chromatography revealed that dCBC contained sublethal CGA concentrations (673.825 ± 6.106 μg/mL), which significantly enhanced biofilm biomass and viable cell counts across a range of temperatures (5, 25, and 35 °C). Biofilm development was characterized by increased protein-rich extracellular polymeric substances (EPS) and reinforced matrix architecture, as confirmed by field-emission scanning electron microscopy (FE-SEM), while early-stage adhesion and aggregation remained unchanged. Metabolic assays further indicate elevated acidogenic activity and reduced reactive oxygen species levels, suggesting that dCBC exposure creates a physiologically favorable environment for biofilm maturation. These findings suggest that sub-inhibitory exposure to phenolic compounds in dCBC may promote biofilm maturation rather than suppression, potentially compromising the hygienic integrity of reusable food-contact surfaces. The study underscores the importance of evaluating beverage-material interactions and optimizing cleaning protocols to ensure microbiological safety in sustainable consumption practices.