Onosma heterophyllum: Phenolic composition, enzyme inhibitory and antioxidant activities

Onosma species have frequently been used for their colouring and dyeing properties in foods and medicinal preparations. The antioxidant and enzyme inhibitory activities of the ethyl acetate, methanol and water extracts of Onosma heterophyllum (Griseb.) are described. Phytochemical compositions of these extracts were also determined. The water extract showed not only remarkable antioxidant activity in all assays but also considerable inhibitory activity on tyrosinase and a-glucosidase (112.44 mu mol KAEs/g dry plant and 984.36 mu mol ACEs/g dry plant, respectively). The methanol extract exhibited the highest inhibitory activity on acetylcholinesterase (AChE) and cc-amylase (79.18 mu mol GALAEs/g dry plant and 10.42 mu mol ACEs/g dry plant, respectively). Chromatographic analyses revealed that the water extract was found to be rich in phenolic and flavonoid contents. On the basis of the correlation coefficients calculated separately for all experimental parameter pairs, protocatechuic acid, p-hydroxybenzoic acid, syringic acid, p-coumaric acid and luteolin were found to be highly in correlation with the antioxidant and enzyme inhibitory activities. This study demonstrates that O. heterophyllum, contained in food preparations with various purposes for many years, could be used for the treatment of diabetes as well as its skin whitening effect.