3,6-Anhydro-l-galactose, a rare sugar from agar, a new anticariogenic sugar to replace xylitol

•3,6-Anhydro-l-galactose (AHG) is a rare sugar from agar of red macroalgae.•AHG inhibited the cell growth and acid production by Streptococcus mutans.•Inhibitory effect of AHG on S. mutans was significantly higher than xylitol.•AHG is considered as a new anticariogenic sugar to prevent dental caries.

The significance for anticariogenic sugar substitutes is growing due to increasing demands for dietary sugars and rising concerns of dental caries. Xylitol is widely used as an anticariogenic sugar substitute, but the inhibitory effects of xylitol on Streptococcus mutans, the main cause of tooth decay, are exhibited only at high concentrations. Here, the inhibitory effects of 3,6-anhydro-l-galactose (AHG), a rare sugar from red macroalgae, were evaluated on S. mutans, in comparison with those of xylitol. In the presence of 5 g/l of AHG, the growth of S. mutans was retarded. At 10 g/l of AHG, the growth and acid production by S. mutans were completely inhibited. However, in the presence of xylitol, at a much higher concentration (i.e., 40 g/l), the growth of S. mutans still occurred. These results suggest that AHG can be used as a new anticariogenic sugar substitute for preventing dental caries.