Only C. arabica and C. canephora extracts prepared from beans
roasted for 6 and 7 min inhibited the bacterial growth (MIC of
5 mg/mL). Differently from the regular samples, extracts from
decaffeinated beans roasted for 8 min did not show inhibitory
activity. Additionally, none of the decaffeinated extracts inhibited
the biofilm formation. Although in the present study caffeine alone
did not exert inhibitory activity on the growth of S. mutans, studies
performed by Daglia et al. (2007) and Almeida et al. (2004) observed that at concentrations of 5.0 and 2.0 mg/mL, respectively,
caffeine provided antimicrobial activity against S. mutans. These
authors also showed that caffeine was able to enhance the inhibitory effect of coffee compounds. This could explain why decaffeinated
coffee roasted for 8 min did not show inhibitory effect. Furthermore,
other possibly inhibitory compounds may have been
washed out by water and dichloromethane during decaffeination
process. As in regular samples, a significant inverse correlation
was found between roasting degree and inhibitory activity among
decaffeinated samples (Table 4). Group 2 samples did not show
biofilm reduction at tested concentrations.