Apart from the activity of phenolic compounds, another
coffee bioactive compound such as caffeine could contribute
to the mutagen inhibition. Caffeine standard solutions had high
inhibition percentages (33–56%) against the mutagenic agent,
showing a dose-dependent pattern. In order to better simulate
different spent coffee and coffee brew matrices, mixtures
of low, medium and high concentrations of 5-caffeoylquinic
acid and caffeine were also tested. The results from 5-CQA and
caffeine mixtures did not show any additional or synergistic
effects, because similar inhibition percentages have been found
when comparing with individual standards (40–53%). The mixtures
of similar amounts of both compounds (750/700 and 320/
350 g/plate) were more efficient. Therefore, these last results
could partially explain the highest inhibition percentage observed
in Robusta spent coffee extract with similar
concentrations of naturally-occurring CQAs and caffeine. Nevertheless,
coffee samples were less effective than standard
solutions, probably due to the presence of many other compounds,
which may act as antagonists.