Effect of pH on the Antimicrobial Activity of Wood Vinegar (Pyroligneous Extract) From Eucalyptus

Abstract The study aimed to assess the effect of progressive neutralization on the antimicrobial properties against bacteria and yeasts of wood vinegar obtained from the pyrolysis of Eucalyptus urograndis wood. Wood samples were carbonized at a heating rate of 0.7°C min1 until a final temperature of 450°C. The raw pyrolysis liquids were left to settle and the aqueous fraction was separated. Then, the aqueous fraction (raw wood vinegar – WV) was purified to yield the WV. WV samples were collected and neutralized in steps with a solution of 2-mol L− 1 NaOH from pH 2.5 until 7.5 (2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, and 7.5. Through the broth microdilution method, the antimicrobial effect of the neutralized samples at each pH was assessed on Pseudomonas aeruginosa (ATCC 27853), and Salmonella enteritidis (ATCC 13076), Staphylococcus aureus (ATCC 25923), Streptococcus agalactiae (CEPA CLINICA), and Candida albicans (ATCC 10231). The minimum inhibitory concentration (MIC) and minimum bactericidal (and fungicidal) concentrations were determined. Results were submitted to regression analysis, and statistical models were fitted. A progressive decrease in the antimicrobial activity was determined as pH increased. Nevertheless, even when neutral and slightly alkaline pH values are reached, the inhibitory activity remained at a certain level. Higher pH values of the WV were associated with lower antimicrobial activity. However, its activity remained even at neutral and slightly alkaline pH values. The results demonstrated the effect of pH on the antimicrobial effect of WV, a product with applications in veterinary medicine and zootechnics.