Optimized extraction of Pinus taeda knotwood sawmill residues as source of antifungal compounds

In Uruguay, Pinus taeda is the dominant conifer in industrial plantations, generating large volumes of knot-containing offcuts during processing. These residues are highly enriched in extractives, offering opportunities for valorization within a circular bioeconomy. This study examined the recovery of bioactive compounds from P. taeda knotwood through ethanol extraction, process optimization, Gas Chromatography coupled with Mass Spectrometry and Flame Ionization Detection (GC-MS/FID) analysis, and antifungal evaluation. The effects of extraction temperature, ethanol concentration, and liquid-solid (L/S) ratio on extraction yield, total phenolic content, and FRAP antioxidant activity were assessed, and response models were developed to identify optimal conditions. Maximum extraction yield (20.8%) occurred at 47 °C, 100% ethanol concentration, and L/S of 8.3. The highest phenolic content (5.7 g gallic acid equivalents/100 g) was predicted at 61 °C, 100% ethanol, and L/S 15, while the greatest antioxidant capacity (15.8 mmol ascorbic acid equivalents/100 g) was achieved at 75 °C and L/S 15, independently of ethanol concentration. Two extraction conditions, representing the best compromise among yield, phenolics, and antioxidant performance, were selected for further characterization and antifungal tests. GC-MS/FID analysis showed that stilbenes and terpenoids dominated the extracts. Antifungal assays against Trametes versicolor and Gloeophyllum trabeum revealed strong inhibition, reaching up to 65% and 97% after seven days. Overall, the results demonstrate that P. taeda knotwood residues can be efficiently valorised via ethanolic extraction to obtain bioactive fractions with high antioxidant and antifungal activity, supporting sustainable and circular approaches for wood protection.