Durability of rubberwood (Hevea brasiliensis) treated with peppermint oil, eucalyptus oil, and their main components

Anti-fungal activities of two essential oils (peppermint oil and eucalyptus oil) and their main components (menthol and eucalyptol, respectively) against molds (Aspergillus niger, Penicillium chrysogenum, and Penicillium sp.) and a white-rot decay fungus (Trametes versicolor) identified from rubberwood surfaces were investigated. The broth dilution method and the agar diffusion technique were employed to determine the minimal inhibitory concentration (MIC) and the minimal fungicidal concentration (MFC) using the concentration of substances between 100 and 800 mu l ml(-1). Inhibitory effects of essential oils and their main components at the MICs against mold growth, fungal decay, and termite attack on rubberwood were further examined by means of the dip treatment method. It was found that MFC values against molds for all treatments examined were about 50-100 mu l ml(-1) higher than MIC values. Peppermint oil and menthol exhibited high fungistatic and fungicidal activities, with MICs of 300 mu l ml(-1) and 350 mu l ml(-1), respectively, against the test molds and the decay fungus. Eucalyptus oil and eucalyptol were also effective against these microbes but at higher concentrations of 600 mu l ml(-1) and 500 mu l ml(-1), respectively. Only peppermint oil at the MIC was capable of providing a complete protection from mold growth on rubberwood for up to 12 weeks at storage conditions of 25 degrees C and 100% RH. Both peppermint oil and eucalyptus oil at the MICs showed moderate resistance to fungal decay and high resistance to termite attack. (C) 2009 Elsevier Ltd. All rights reserved.