Substrate-Driven Differential Sensitivity of Gram-Positive and Gram-Negative Bacteria to Pine and Birch Liquid Pyrolysis Products

Recent studies have shown that wood tar exhibits excellent potential as an additive to polymers for food packaging. In this study, we demonstrated that the differential temperature of dry pyrolysis of wood affects the antioxidant and antibacterial activities of the liquid pyrolysis products (LPP). Birch LPP showed, on average, approximately 16% higher reducing power in the ferric-reducing antioxidant power (FRAP) assay and, on average, approximately 29% lower free radical scavenging activity than pine LPP. Thermal characterization suggests a qualitatively similar chemical composition among the tested fractions, with the 500 °C pyrolysis fraction showing the highest thermal resistance (lowest mass loss). Thermal characterization indicated similarities in the qualitative chemical composition of the tested fractions. Analyzed products demonstrated bactericidal activity against human- or plant-pathogenic bacteria and exhibited poor antimicrobial activity towards probiotic bacteria. Specifically, Lactoplantibacillus sp. and L. rhamnosus were, on average, approximately 61% and 45% less affected, respectively, compared to the most sensitive E. coli. We demonstrate apparent, predominantly substrate-driven differences in antibacterial activity, with Gram-negative bacteria being more susceptible to pine products and Gram-positive bacteria being more susceptible to birch products.