Peppermint Essential Oil Suppresses Geotrichum citri-aurantii Growth by Destructing the Cell Structure, Internal Homeostasis, and Cell Cycle

Peppermint essential oil (Peo) is an efficient antifungal agent, and 2.0 mu L of Peo per milliliter culture medium can completely inhibit the mycelium growth and spore germination of Geotrichum citri-aurantii. In vitro experiments showed that the main functional component in Peo was L-menthol, which could lead to changes in sugar and protein contents, reduce the content of alkaline phosphatase (AKP), and destroy the spore membrane structure, with a significant increase in electrical conductivity. Meanwhile, the content of reactive oxygen (ROS) accumulated sharply, and the enzyme activity changed significantly with the change in the gene expression level. In addition, L-menthol could cause degradation in spore genetic material differently. Furthermore, a total of 1704 differentially expressed genes (DEGs) in G. citri-aurantii after 1.6 mu L/mL L-menthol exposure for 2 h were obtained by the transcriptome sequencing. These DEGs were involved in transmembrane transport, carbohydrate transmembrane transport protein activity, and mitogen-activated protein kinase (MAPK) signaling pathway. The protein-protein interaction (PPI) analysis of DEGs yielded 10 highly cross-linked nodes, and these genes were associated with DNA replication and cell cycle. The expression level of the hub gene was confirmed by real-time quantitative PCR (RT-qPCR), with the most significant changes in POL 30 (5.9-fold). Molecular simulation was performed and it was found that the binding site between L-menthol and POL 30 was the 44th ARG residue in POL 30, and it was speculated that L-menthol and POL 30 may be combined by hydrogen bonding interaction. The results of flow cytometry assay showed that L-menthol blocked the replication process in the S-phase of G. citri-aurantii. This study provides new insights into the development and application of Peo in food safety.