Abstract
The in vitro antifungal activity of tea tree oil (TTO), the essential oil of Melaleuca alternifolia, has been evaluated against the mycotoxin producer Aspergillus parasiticus. The minimum inhibitory concentrations (MICs) of tea tree oil were 2% and 4% (v/v), for broth microdilution assay and agar dilution assay, respectively, whereas the minimum fungicidal concentration (MFC) obtained by the two methods was 8% (v/v). Inhibitory effects on mycelial growth and sporulation of A. parasiticus due to treatment with different concentrations of TTO were observed. Moreover, growth of A. parasiticus on barley grains treated with TTO concentrations at 1% and 2% v/w was reduced. At concentration of 4% v/w of TTO fungal growth and grain colonization by A. parasiticus were prevented completely. Negative linear relationships between oil concentrations and dry weight as well as ergosterol content with correlation coefficients of – 0.85 and - 0.80 respectively, were detected. However, a positive linear relationship between the dry weight and ergosterol was reported with correlation coefficient of + 0.99. TTO was effective in inhibiting aflatoxins (AFB1, AFB2, AFG1, and AFG2) accumulation, with maximum inhibition percentage 67.4, 64.9, 72.6, and 67.3 % at 1% v/v, respectively. Growth, sporulation, ergosterol content and aflatoxins accumulation were inhibited by the oil in a dose-dependent manner.

Key words: Tea tree oil, A. parasiticus, growth, sporulation, ergosterol, aflatoxins