Lignin as natural radical scavenger. Effect of the obtaining and purification processes on the antioxidant behaviour of lignin

In the present work, the antioxidant activity of 14 lignin samples obtained from apple tree pruning\r\nwas studied. Different solvents (water, soda–water 7.5% (w/w), ethanol–water 60:40 (v/v) and acetic\r\nacid–water 60:40 (v/v)) under different operation conditions were used in order to extract the lignin\r\nand different techniques (ultrafiltration, differential precipitation and lignin purification) were applied\r\nwith the aim of improving the lignin properties. The obtained lignin samples were characterized by\r\ndifferent analytical techniques evaluating their chemical structure (ATR-IR), thermal behaviour (TGA and\r\nDSC) and molecular weight (GPC). Further analyses (13C NMR and Folin–Ciocalteu method) were carried\r\nout in order to determine the purity and the total phenolics content present in the lignin samples. The\r\nantioxidant activity of the analyzed lignins was evaluated by the radical ABTS assay. The results revealed\r\nthe high influence that the lignin obtaining process had on the lignin properties, determining its possible\r\ncommercial application. Results also indicated that autohydrolysis, organosolv and some ultrafiltrated\r\nsoda lignins showed antioxidant efficiency comparable with a powerful natural antioxidant, as catechin,\r\nand a commercial one, Trolox®.