Extraction of antioxidant phenolics from almond hulls (Prunus amygdalus) and pine sawdust (Pinus pinaster)

Lignocellulosic residues, such as pine sawdust and almond hulls, were solvent-extracted under different experimental conditions to optimize the yield of polyphenolic antioxidant compounds, which were quantified. The antioxidant power of extracts was evaluated by ability to scavenge the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical. Both materials were found to be important sources of phenolic antioxidants, although the efficiency of the extraction varied with the experimental conditions. Among the three solvents used (ethanol, methanol and water), ethanol was the most favourable for total extractables, although methanol was more selective for extracting polyphenolics. For these latter, pine sawdust offered the best results, with a 3–10 times higher (0.1122 g/100 g in dry basis) total phenolics content than almond hulls but, despite this, phenols from hulls showed a higher antioxidant capacity (58 vs 34% of inhibition).