Chemical and bioactivity profiles of needle-rich Norway spruce logging residue fractions

Norway spruce logging residues, an abundant byproduct of timber harvesting for wood products, pulp, and paper industries, are primarily composed of wood, needles, and bark. The latter two are rich in phenolic compounds, known for their antioxidant and antimicrobial properties. However, variations in compound profiles and bioactivities can arise due to differences in plant organ composition, seasonal changes, and processing conditions. In this study, the aim was to evaluate the differences in fractions obtained across different seasons and through three processing/assortment methods. The effectiveness of two industrial assortment procedures was compared with that of hand-picked pure fractions of needles, branch bark, and branch wood, and the volatile organic compound (VOC) profile of pure fractions was analyzed. As expected, the hand-picked needle fraction exhibited high antioxidant and antibacterial properties, and these activities correlated positively with the amount of stilbenes and flavonoids in the extracts. Additionally, an assortment processed without a drying cyclone preserved the freshness of the fractions and produced needle-rich fractions with a bioactivity profile comparable to hand-picked needles. Due to seasonal differences and assortment efficiency, antiviral efficacy against enterovirus (coxsackievirus A9) was lower in both the first assortment and hand-picked fractions, both obtained in spring, while even low concentrations of fall assortment fractions showed high efficacy. VOC profiles of the hand-picked fractions revealed that needles contained the highest number and amount of compounds. The results highlight that mechanical separation enables efficient recovery of valuable needle fractions, offering valuable insights for the future utilization of spruce logging residues in biorefineries.