Abstract
Heat treatment is the most commonly practiced technology to add value to products derived from wood materials. Traditionally, heat treatment enhances the resistance of wood materials to weathering and decay fungi, but despite its wide use in sectors such as construction, wood preservation and food packaging, there has been little attempt to apply heat treatment in other areas to manage food-borne and plant diseases. A preliminary study indicated that preheating increased the inhibitory effect of pine wood shavings against the important food-borne pathogen of broilers, Salmonella Enteritidis (SE). Thus the first objective of this study was to optimise a heating regime to evaluate the effect of the enhanced inhibitory activity on SE in direct contact and also reducing ammonia emission of a constructed litter using heated wood. Heating to 120°C for 72 hours was the most effective treatment. In addition, heated pine wood had antimicrobial activity against other known microorganisms in poultry bedding including Staphylococcus aureus, Escherichia coli and Saccharomyces cerevisiae as well as SE. Hardwood shavings of ash, beech, red oak also showed antimicrobial activity against SE as did similarly treated softwood species such as pine and cypress. In vitro assays of dominant chemicals derived from fractionation of the extract demonstrated that bio-active fractions containing vanillin and dehydroabietic acid exhibited antimicrobial activity, but weak or no activity after purification. Overall, the in vitro assays suggested that a synergistic interaction occurred between vanillin and dehydroabietic acid decreasing the minimum inhibitor levels of vanillin. A second objective of the study was to investigate the potential of heat-treated woodchips of Japanese larch and rhododendron to control Phytophthora ramorum (PR) an invasive pathogen of larch in UK forests. Results demonstrated that heat-treated pine, larch and rhododendron woodchips inhibited the recovery of zoospores of PR compared with air-dried woodchips. This inhibition was maintained even if the larch woodchips were diluted with soil. The in vitro assays revealed that their methanol crude extracts had an inhibitory effect on PR zoospores and also reduced germination of chlamydospores compared with extracts from air-dried wood. Chemical analysis of crude extracts of all three showed some of the induced compounds were present in all the extracts but differed in concentration. Coniferaldehyde was the most active compound against all three propagules. The dominant resin acids, DHAA and abietic acid (AB) decreased the minimum inhibitory level of the tested phenolic compounds against PR but had no effect when tested alone. Results of a field trial using heat-treated and air-dried woodchips were consistent with the bioassay results of crude extracts and indicated that heat treated materials have potential to reduce the survival of PR under natural conditions. Finally, based on overall results of bioassays in both parts of this study a mechanism of action for the synergism between aromatic compounds such as vanillin and coniferaldehyde and resin acids dehydroabietic and abietic acid was hypothesized.