Effects of α-amylase and its inhibitors on acid production from cooked starch by oral streptococci

This study evaluated acid production from cooked starch by Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguinis and Streptococcus mitis, and the effects of α-amylase inhibitors (maltotriitol and acarbose) and xylitol on acid production. Streptococcal cell suspensions were anaerobically incubated with various carbohydrates that included cooked potato starch in the presence or absence of α-amylase. Subsequently, the fall in pH and the acid production rate at pH 7.0 were measured. In addition, the effects of adding α-amylase inhibitors and xylitol to the reaction mixture were evaluated. In the absence of α-amylase, both the fall in pH and the acid production rate from cooked starch were small. On the other hand, in the presence of α-amylase, the pH fell to 3.9-4.4 and the acid production rate was 0.61-0.92 μmol per optical density unit per min. These values were comparable to those for maltose. When using cooked starch, the fall in pH by S. sanguinis and S. mitis was similar to that by S. mutans and S. sobrinus. For all streptococci, α-amylase inhibitors caused a decrease in acid production from cooked starch, although xylitol only decreased acid production by S. mutans and S. sobrinus. These results suggest that cooked starch is potentially acidogenic in the presence of α-amylase, which occurs in the oral cavity. In terms of the acidogenic potential of cooked starch, S. sanguinis and S. mitis were comparable to S. mutans and S. sobrinus. α-Amylase inhibitors and xylitol might moderate this activity.