Identification of terpenoids volatilized from Thymus vulgaris L. by heat treatment and their in vitro antimicrobial activity

•Volatile organic components of Thymus vulgaris have antimicrobial activity.•Thyme volatile components inhibited Botrytis cinerea mycelial growth after heat treatment.•Thymol, p-cymene, and γ-terpinene were the main volatile compounds.•The biosynthetic gene expression of γ-terpinene tended to increase after heat treatment.•Heat treatment of Thymus vulgaris may be useful for plant disease control.

Enhanced antifungal activity by hot water treatment at 50 °C 20 s against Botrytis cinerea Pers. ex Fr., a gray mold pathogen was evaluated in thyme (Thymus vulgaris L.) Thymol, p-cymene, and γ-terpinene were detected as the main volatile compounds in thyme plants. Emission of p-cymene and γ-terpinene from thyme increased after treatment, whereas amount of thymol released did not change, suggested that existence of a thermo-dependent synthesis pathway of p-cymene and γ-terpinene. Volatile p-cymene inhibited mycelial growth of pathogen at 0.50 μL/ml, whereas γ-terpinene had an inhibitory effect at 0.05, 0.10, and 0.50 μL/ml. Transcript level of γ-terpinene gene increased after 24 h of treatment. As a conclusion, heat treatment enhanced antifungal activity by volatile terpenoids synthesized by thermo-dependent synthesis pathway of them in thyme.