Preparation, chemical constituents and antimicrobial activity of pyroligneous acids from walnut tree branches

To achieve a comprehensive utilization of walnut tree branches, a waste from the cultivation of walnut fruit, pyroligneous acids were prepared and collected by pyrolyzing walnut tree branches at three temperature ranges, 90–230 °C, 230–370 °C and 370–450 °C. Antimicrobial activity of each pyroligneous acid was tested. Chemical constituents of the pyroligneous acid collected from 230 to 370 °C, which showed the strongest antimicrobial activity were analyzed by GC-MS. The results showed that the temperature range to produce pyroligneous acid from walnut tree branches was 90–450 °C. All the pyroligneous acids collected from three temperature ranges showed antimicrobial activities, while the pyroligneous acid collected from 230 to 370 °C showed strongest antimicrobial activity. Fifty compounds were found by GC–MS analysis from the pyroligneous acid collected at this temperature range, namely organic acids, phenols, ketones phenyl ethers, and furan and pyran derivatives, others with lower contents were alcohols, esters, sugar derivatives, and nitrogen compounds. Phenols and organic acids accounted for 63.46% of the total constituents detected. It is suggested that phenols and organic acids are the active components for antimicrobial activity.