α-terpineol and terpene-4-ol, the critical components of tea tree oil, exert antifungal activities in vitro and in vivo against Aspergillus niger in grapes by inducing morphous damage and metabolic changes of fungus

Abstract

Concerns about Aspergillus niger (A. niger) contamination and subsequent overuse of synthetic preservatives in foods have arisen due to their potential threats on human health and the environment. Essential oils from plants, and some of the oils’ active components as natural antimycotics, are predicted to inactivate A. niger. In this study, the antifungal activities and mechanisms of tea tree oil (TTO) and its main components were investigated as potential substitutes for synthetic preservatives. TTO is recognized as a safe essential oil, and chemical compositions of TTO were analyzed by gas chromatography-mass spectrometry, with terpene-4-ol, α-terpineol and 3-Carene identified as its main components. The inhibitory effects of TTO and its main constituents against A. niger were compared. α-terpineol and terpene-4-ol exhibited the greatest effectiveness at inhibiting mycelium growth and spore germination. The most serious destruction to cytomembrane permeability, and interference in microscopic morphology of hyphae and spores, as well as metabolic pathways of A. niger, was strongest with these two components -- even stronger than complete TTO treatments. 3-Carene showed little inhibitory effect. α-terpineol and terpene-4-ol also possess the best preservative effects which combat against black mold disease caused by A. niger in postharvest grapes. Overall, α-terpineol and terpene-4-ol possess strong antimycotic effects which contribute largely to the antifungal activity of TTO. Further studies on evaluating the effectiveness of combined usage of purified α-terpineol and terpene-4-ol against A. niger growth in different foods should be implemented to better control the risk of A. niger-mediated diseases.