IMPROVEMENT OF ANTIFUNGAL ACTIVITY OF CITRONELLA OIL AGAINST <em>ASPERGILLUS</em> <em>FLAVUS</em> ON RUBBERWOOD (<em>HEVEA</em> <em>BRASILIENSIS</em>) USING HEAT CURING

Abstract

Optimisation of the inhibitory effect of citronella oil (10, 30 and 50 μg mL^-1) with heat curing (30, 90 and 150 °C) and drying periods (1, 12 and 24 hours) against a major mould (Aspergillus flavus) found on the surface of rubberwood was investigated using response surface methodology. Specimens were incubated at 25 °C in 100% relative humidity for 90 days and individually rated for the period it took to achieve zero mould growth on rubberwood. Citronella oil components were analysed by gas chromatography–mass spectrometry. Citronella oil (50 μg mL^-1) with heat curing (30 and 90 °C) and drying periods (1 to 24 hours) completely inhibited spore germination for at least 90 days. Microscopy investigation confirmed that no spore germination was found in treated rubberwood. Citronellal (27.5%), geraniol (20.4%), citronellol (13.4%) were major constituents of citronella oil. Heat curing may be important for transformation of components and enhancement of antifungal activity of citronella oil. This study showed that a combination of citronella oil and heat curing could protect rubberwood.