Impact of extraction processes on phytochemicals content and biological activity of Citrus x clementina Hort. Ex Tan. leaves: New opportunity for under-utilized food by-products

Plants are a rich source of natural bioactive compounds with a wide range of applications in the food and pharmaceutical industries. Citrus x clementina leaves extracts and essential oils may be a potential candidate for formulation of products characterized by hypoglycaemic, antioxidant and anti-browning properties. C. x clementina leaves collected in three different areas in Calabria (South Italy) were extracted by Soxhlet apparatus, maceration, Ultrasound assisted maceration, and hydrodistillation. Hesperidin, tangeritin, and sinensetin were identified by HPLC-DAD analysis as dominant constituents of the extracts. The absence of coumarins and furanocoumarins was demonstrated. GC-MS analyses of essential oils evidenced the presence of sabinene, linalool, and (E)-beta-ocimene as main compounds. Based on RACI and GAS values calculated by the integration of data obtained by DPPH, ABTS, FRAP and beta-carotene bleaching methods, hydroalcoholic extract obtained by Ultrasound assisted maceration of the leaves collected in Corigliano Calabro showed the highest antioxidant activity. Ultrasound assisted hydroalcoholic extract of Cetraro leaves revealed the highest a-amylase inhibitory activity (IC50 of 64.37 mu g/ml). Promising results of C. x clementina extracts as tyrosinase inhibitors were also obtained. To evaluate the relationship between identified compounds and bioactivity PCA was performed. Taking into account results obtained by this study, C. x clementina leaves that were considered Citrusby-products could be utilized for formulation of food additives, nutraceuticals and functional foods.