Thermochemical Valorization of Silkworm Feeding Waste: Chemical Characterization and Biological Activities of the Pyrolysis-Derived Liquid Fraction

Silkworm-rearing residues are an underused biomass resource that can be converted into value-added products. In this study, a condensable liquid product (SWP-Liq) was produced from these residues by pyrolysis at 325 ± 5 °C and evaluated for its chemical composition and in vitro biological activities. SWP-Liq yielded phenolic-, flavonoid-, and triterpenoid-equivalent values of 218.47 ± 22.40 mg GAE/g, 79.13 ± 3.55 mg QE/g, and 55.54 ± 6.15 mg EE/g, respectively. The ABTS•+ assay showed a higher radical-scavenging response than DPPH, while Fe3+- and Cu2+-reducing activities were also observed. SWP-Liq inhibited 5-LOX with an IC50 of 33.05 ± 1.10 µg/mL, whereas α-glucosidase inhibition was weaker. Antibacterial activity against all four tested bacterial species was observed at 8 mg/mL but not at 4 mg/mL. Targeted LC–MS/MS quantified five phenolic constituents, with p-coumaric acid (1599.71 µg/g), chlorogenic acid (871.43 µg/g), and ferulic acid (285.50 µg/g) being the most abundant. Overall, these findings support the further investigation of silkworm feeding waste as a feedstock for thermochemical valorization into chemically and biologically evaluable bio-based fractions.