Study of Tunisian nettle leaves (Urtica dioica L.): mineral composition and antioxidant capacity of their extracts obtained by maceration and supercritical fluid extraction

International audienceThis work was undertaken to explore the potential of extract of leaves Nettle (Urtica dioica L.) of Tunisia as sources of minerals and natural antioxidants. Two extraction methods were used and compared, the supercritical fluid extraction (SFE) with carbon dioxide (CO2) and traditional maceration extraction using ethanol (EtOH) as solvent. The SFE was explored at various operating conditions of pression (15 and 18 MPa) and temperature (40 and 60°C) (with or without glass beads). The phenolic and flavonoid contents were determined respectively by Folin-Ciocalteu and Aluminium chloride colorimetric method. The ABTS assay was used for determining the antioxidant activity. The protein assay was performed by the Kjeldahl method and the multielemental analysis by atomic emission spectrometry with inductively coupled plasma. The results show some variations between both extracts in terms of extraction yield and antioxidant activity. The SFE, with carbon dioxide (SC-CO2) is an interesting alternative to the conventional extraction using organic solvents. However, higher values of phenolic content (11.62 mg GAE.g-1 DW), flavonoid content (7.10 mgCE.g-1DW) and antioxidant activity TEAC (8.11 μM) correspond to extracts obtained by maceration. In all SFE extract assays, the highest yield was reached at 60°C – 15MPa with glass beads (2.5%). The ICP analysis shows the abundance of Urtica dioica L. in calcium (1116 mg.100g-1DW) and magnesium (544). The protein assay showed high content (15.75 %.). The present study indicates that the leaves of Urtica dioica L. of Tunisia are a potential source of minerals, proteins and antioxidant