Three different types of Mediterranean, agro-industrial wastes (olive kernels, grape pomace/seeds, peach kernels), were subjected to two pretreatment processes, a chemical/organosolv and a physicochemical one. The organosolv process included lignocellulosic biomass treatment with formic acid/acetic acid/water (30/50/20, v/v%), for 3 h at 107 degrees C, while the physicochemical method was conducted by immersing the biomass in a water/ethanol (8/92, v/v%), H2SO4 0.32 M, solvent and further exposing the slurry to microwave irradiation (maximum 250 W) for 1/2 h at 150 degrees C. Both processes were evaluated regarding the achieved delignification and the purity of the extracted lignins. The effect of the pretreatment processes onto the structure and thermal decomposition behavior of the extracted lignins was investigated via FT-IR and TGA analysis, respectively. The objective of the research work was to investigate potential valorization routes for these biomass agro-residues in the context of a biorefinery, focusing on lignin extraction. The pretreatment results showed that the obtained lignins, derived from both procedures, were of high purity (> 82 wt%). Under the organosolv procedure, peach kernel delignification showed the maximum value (similar to 16 wt%), while under microwave pretreatment, olive kernel delignification showed the maximum value (similar to 35 wt%). Grape pomace/seeds appeared to be the most resistant in both treatments. (C) 2013 Elsevier B.V. All rights reserved.