Effect of barley coffee on the adhesive properties of oral streptococci

Rapid advances in scientific knowledge supporting the vital role of diet foods in health and disease prevention have been made recently. Caries is an infectious disease for which Streptococcus mutans is considered the principal etiological agents in humans. S. mutans adhesion to tooth surface is a crucial step in dental caries initiation and development. A promising approach for caries preventions is based on the inhibition of such process. Some beverages and foods are known to protect against S. mutans colonization of dental surface; we have recently shown that roasted coffee interferes with S. mutans adsorption to hydroxyapatite (HA). In the present work the antibacterial and antiadhesive properties of barley coffee (BC), a beverage obtained by roasted barley grains and frequently used as coffee substitute, was studied and components responsible for the found activities were identified and isolated. Three experimental approaches were followed to evaluate the effects of BC sub-lethal concentrations (sub-MICs) on S. mutans adherence to saliva-coated HA beads: BC and bacteria were added simultaneously to HA beads; streptococci were pre-treated with BC before addition of bacteria; streptococci grown in the presence of BC were added to HA. All treatments caused a statistically significant, dose-dependent inhibition of S. mutans sucrose-dependent and sucrose-independent adherence to HA. BC components were fractionated by dialysis; the MM<1000Da fraction, containing polyphenols, zinc and fluoride ions, and the MM>100KDa fraction, consisting of a brown potent antioxidant melanoidin, showed anti-adhesive properties. The high MM melanoidin was not found in the natural barley, indicating that it originates in barley grains during the roasting process. These results suggest that BC consumption might influence colonization of tooth surfaces by cariogenic bacteria.