Combined coulometric and voltammetric analytical approach provides novel insights into the antioxidant capacity of natural coumarins and furanocoumarins

Despite intense investigation on the subject, the information available on the antioxidant capacity of natural coumarins and furanocoumarins is controversial. In the present study the antioxidant capacity of 19 pure naturally occurring compounds, among which 5 coumarins and 14 furanocoumarins is determined, using both the coulometrically determined antioxidant capacity (CDAC) and linear sweep voltammetry (LSV). None of the coumarins and furanocoumarins assayed exhibited appreciable scavenging activity against the DPPH radical. In contrast, they were differently reactive against Br2. While coumarin did not show detectable CDAC, its 7-hydroxy derivative, namely umbelliferon, had a strikingly high CDAC value (35 mmol e− g−1) that remained unchanged in the pH 5–9 range. The presence of 5-alkoxy substituents appeared to increase critically the CDAC values so that bergapten (5-methoxypsoralen) exhibited the highest CDAC value (12 mmol e− g−1) among the assayed furanocoumarins. For all the compounds investigated, CDAC and LSV values were strictly correlated (R2 = 0.91). These findings suggest that complex mechanisms beyond pure hydrogen atom transfer or electron transfer and not only related to reactivity with Br2 may concur to determine the antioxidant capacity of coumarins. CDAC and LSV of non-volatile fraction of bergamot peel essential oil and its defurocoumarinized counterpart were investigated as real coumarins- and furanocoumarins-rich real samples. Owing to the predominant persistence of bergamottin, removal of bergapten did not significantly reduce the antioxidant capacity, while it minimizes the risks associated with phototoxicity.