In vitro evaluation of antimicrobial efficacy of pyroligneous acid from softwood mixture

A novel technology was developed to obtain a high amount of pyroligneous acid (PA) rich in organics. PA was obtained by atmospheric pyrolysis of a mixture of pine, spruce and fir wood particles, analyzed by gas chromatography-mass spectrometry (GC–MS) and evaluated for in vitro antibacterial and antifungal activity. Several microbial inhibitory compounds were observed in PA. Antimicrobial activity of PA was studied at both acidic pH (3.7) and neutral pH (7.0) of the liquid. Neutralized PA showed higher antibacterial activity than acidic PA against 5 pathogenic bacterial strains, and Minimum Inhibitory Concentration (MIC) obtained with neutralized PA were 0.3125% (v/v), 0.3125% (v/v), 0.625% (v/v), 0.3125% (v/v), 0.3125% (v/v) for Escherichia coli, Enterobacter aerogenes, Pseudomonas aeruginosa, Listeria monocytogenes and Enterococcus faecalis, respectively. For fungal strains, acidic PA was found to be more effective than neutralized PA. The highest activity was against Trametes versicolor, followed by Aspergillus niger and Aspergillus fumigatus. The MIC of acidic PA with which fungal inhibition was seen was 0.125% (v/v) for T. versicolor and A. fumigatus, and 0.25% (v/v) for A. niger. Hence, the novel technology was found to be effective to produce a high yield of PA (40–45 wt% of dry biomass), rich in antimicrobial compounds, and the PA is proposed as a potential alternative to antibiotics, preservatives and/or chemical disinfectants that are currently in use.