Supercritical fluid extraction vs conventional extraction of myrtle leaves and berries: Comparison of antioxidant activity and identification of bioactive compounds

In this work, the antioxidant capacity of extracts of Portuguese myrtle (Myrtus communis L.) is being studied over a period of three years. The samples were leaves of myrtle collected at the flowering stage and berries sampled at an early ripened stage. Supercritical fluid extraction (SFE) extracts were obtained at 23 MPa, 45°C and a CO₂ flow of 0.3 kg h^-1 using ethanol as co-solvent with a flow rate of 0.09 kg h^-1. Hydrodistillation was carried out in a Clevenger type apparatus and the aqueous phase was extracted with diisopropylether having obtained what is hereby designated as liquid phase extract (LPE). The antioxidant capacity of all the extracts was determined by using three different methods: the Folin-Ciocalteu, the Trolox Equivalent Antioxidant Capacity (TEAC) and the Oxygen Radical Absorbance Capacity (ORAC). The results show that the SFE extracts present a significantly higher antioxidant capacity. The extracts were characterized and quantified by HPLC-DAD-MS/MS methods. The bioactive compounds identified in all the extracts were phenolic acids (only in the LPE extracts), flavonoids and anthocyanins (only in the SFE extracts). The results indicate that the higher antioxidant capacity of the SFE myrtle extracts is mainly correlated with the concentration of flavonol glycosides, the myricetin-O-glycosides.