Unlocking the potential of undervalued forest residues: a comprehensive characterization of eucalypt stumps in the biorefinery context

Eucalyptus globulus stumps were fractionated in three Discs, and their constituent tissues - heartwood, sapwood and bark - subjected to further chemical characterization by summative analysis, evaluation of the phytochemical profile and antioxidants activities, plus GC/MS and analytical pyrolysis. Wood density was similar between tissues and Disc level: values ranging from 0.652 to 0.705 g/cm³ (Disc 1) and 0.605 g/cm³ (Disc 5). Bark had high ash (3.5%), extractives (7.5%) and holocellulose (68.4%) but lower lignin contents (22.0%). Original heartwood contained 0.7% ash, 7.0% extractives, 27.1% lignin, and 67.3% holocellulose. Heartwood showed high extractives (12.1-15.8%), less lignin (23.9-24.5%), and high holocellulose (61.7-64.7%) than sapwood containing 3.9-5.4% extractives, 26.9-27.3% lignin and 68.6-71.5% holocellulose. Water extracts had poor antioxidant activity in contrast to ethanol extracts which activities were the highest in heartwood. All tissues presented GS lignin type with S/G ratios varying from 3.0-3.4 (heartwood), 3.2-3.4 (sapwood), bark (3.5) and 3.8 (original heartwood). In wood, fibers and vessels were highly lignified with SG and G-lignin respectively; while rays had low lignin with G-type. Light and fluorescence macroscopic observation of the tissues in Disc 1 revealed lower proportion and larger vessels in sapwood and high emission fluorescence at 488nm.