Archeological studies have found that pyrolysis liquids were already used in the time of the Neanderthal. Wood vinegar and other slow pyrolysis liquids are produced as a by-product of charcoal production. However, future business ideas may be the other way round as pyrolysis liquids may replace synthetic chemicals in the form of pesticides and biocides. Directives and regulations related to the sustainable use of pesticides govern and direct plant protection strategies towards a lower use of synthetic chemicals. It is hoped that many mega trends of global policies will boost the use of plant based products given that a reduced reliance on fossil fuel is a general target in the global food and feed production economy. Pyrolysis technology has been actively studied and developed around the world and is linked to the development of the knowledge based bio-economy. The importance and social impact of pyrolysis technologies will also be enhanced because it is a practicable technique in the sustainable use of wastes and biomasses. However, very little scientific evi- dence is available to support efficacy claims of wood vinegar and toxicology assessments of the products used. Wood tar has been investigated a bit more thoroughly. The aim of this review was to clarify the potential of slow pyrolysis liquids in agricultural use, in particular, in pesticide applications. In addition, some of the main challenges in developing novel bio control technologies are discussed and the barriers in the commercialization of biological control agents are revealed.

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History and use of wood pyrolysis liquids as biocide and plant protection product.

The antioxidant and antibacterial activities of wood vinegar from Litchi chinensis, and its components have been studied. The chemical compositions of wood vinegar were analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 17 chemical compounds were identified, representing 83.96% of the compositions in the wood vinegar. Three major components, included 2,6-dimethoxyphenol (syringol, 29.54%), 2-methoxyphenol (guaiacol, 12.36%), and 3,5-dimethoxy-4-hydroxytoluene (11.07%), were found in the wood vinegar. Antioxidant activities of the acids were investigated from the aspects of 1,1-Diphyl-2-picrylhydrazyl (DPPH) free radicals scavenging capacity, superoxide anion radical scavenging capacity, and reducing power. The pyroligneous acid exhibited high antioxidant activity which was comparable to the reference standards (vitamin C and butylated hydroxyl toluene) at the same dose with IC50 values of 36.5 ppm calculated by the DPPH radical scavenging assay, 38.38 g Trolox equivalent/100 g DW by the trolox equivalent antioxidant capacity (TEAC) assay, and 67.9 by the reducing power analysis. Antibacterial activity was evaluated using the disc diffusion and microdilution methods against a group of clinically antibiotic resistant isolates. The major components exhibited broad spectrum inhibition against all the bacterial strains with a range of disc inhibition zoon between 15–19 mm. The minimum inhibition concentration and minimum bactericide concentration against the test strains was ranging in 0.95–3.80 μL/100 μL and 1.90–3.80 μL/100 μL, respectively. Most of the antibiotic resistant strains were more susceptible to the wood vinegar than the non-antibiotic resistant strain except the strain of ornithine resistant Staphylococcus aureus. Based on the chemical profile, it was considered that the strongest antioxidant and antibacterial activity of Litchi chinensis wood vinegar was due to its highly phenolic compositions. This study revealed that the Litchi chinensis wood vinegar is valuable to develop as alternative food antioxidant and antibiotics.

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Chemical Composition, Antioxidant, and Antibacterial Activity of Wood Vinegar from Litchi chinensis

Production, prospects and potential application of pyroligneous acid in agriculture

Pyroligneous acid (PA) is a complex highly oxygenated aqueous liquid fraction obtained by the condensation of pyrolysis vapors, which result from the thermochemical breakdown or pyrolysis of plant biomass components such as cellulose, hemicellulose, and lignin. PA produced by the slow pyrolysis of plant biomass is a yellowish brown or dark brown liquid with acidic pH and usually comprises a complex mixture of guaiacols, catechols, syringols, phenols, vanillins, furans, pyrans, carboxaldehydes, hydroxyketones, sugars, alkyl aryl ethers, nitrogenated derivatives, alcohols, acetic acid, and other carboxylic acids. The phenolic components, namely guaiacol, alkyl guaiacols, syringol, and alkyl syringols, contribute to the smoky odor of PA. PA finds application in diverse areas, as antioxidant, antimicrobial, antiinflammatory, plant growth stimulator, coagulant for natural rubber, and termiticidal and pesticidal agent; is a source for valuable chemicals; and imparts a smoky flavor for food.

Pyroligneous acid-the smoky acidic liquid from plant biomass.

Antifungal and antitermitic activities of wood vinegar produced from Vitex pubescens were evaluated. Three kinds of wood vinegar were produced at three different pyrolysis temperatures, i.e. at 350, 400 and 450 °C. A PDA dilution method was employed to assay antifungal activity of the vinegars with a white-rot fungus Trametes versicolor and a brown-rot fungus Fomitopsis palustris. Termiticidal activity and repellent effect were evaluated by a no-choice test and a choice test with Reticulitermes speratus and Coptotermes formosanus. All wood vinegars exhibited antifungal activity against both fungi. Wood vinegar of 450 °C had the higher activity than those of 400 and 350 °C. It was assumed that acid component contributed to the increase in controlling the growth of fungal. The wood vinegar exhibited antitermite activity to both R. speratus and C. formosanus workers in the no-choice experiment. However, it needed relatively high concentration to obtain the perfect mortality. For instance, the wood vinegar of 10 % concentration was needed to achieve 100 % mortality against C. formosanus, whereas for R. speratus only 3 % of wood vinegar was required. In the direct-choice experiment, wood vinegar had a significantly repellent effect to both termites at the lowest treating concentration of 10 %.

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Antifungal and antitermitic activities of wood vinegar from Vitex pubescens Vahl

The major objectives of this study were to find out the mechanism behind the sapstaining fungal hyphae penetration into wood elements using electron microscope and to evaluate the exact role of phenolic compounds existing in wood vinegar towards the sapstaining fungal growth inhibition. To formulate the new environmental friendly wood preservative, we neutralized (to pH 7) wood vinegar with NaOH and hot water extracts of Pinus densiflora and Quercus serrata saw dusts were used in the media instead of sterilized distilled water to enhance the fungal growth inhibition property of neutralized wood vinegar. The initial calibration of wood extract was done by calculating the specific gravity, tar calculation and total organic content. GC-MS analysis was performed to identify the phenolic compounds and other ingredients present in both neutralized wood vinegar and acidic wood vinegar by chloroform extraction method. Eleven major compounds were identified in acidic wood vinegar and 7 major compounds in neutralized wood vinegar. Ophiostoma polonicum, O. ips, O. flexuosum, O. narcissi and O. tetropii were the sapstaining fungi used in this study against neutralized wood vinegar, extracts of Pinus densiflora and Quercus serrata. More than 2.5% neutralized wood vinegar contained agar plates were showed strong antifungal activity against sapstaining fungi. The Scanning Electron Microscopy image of fungal growth on wood samples showed the phenomenon of fungal penetration into wood elements. Pinus densiflora was used as wood element for SEM analysis.

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S.S Han

Papers

Antifungal activity of neutralized wood vinegar with water extracts of Pinus densiflora and Quercus serrata saw dusts.