Abstract:Penicillium italicum was used as the test fungal species in this study to investigate the antifungal mechanism of the main active ingredients of Ramulus cinnamomi, namely cinnamaldehyde and cinnamic acid. The mechanisms of the action of cinnamaldehyde and cinnamic acid were identified by evaluating their effects on spore germination, cell membrane permeability, mycelial morphology, soluble sugar content, and the activities of key metabolic enzymes. Results showed that the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC) of cinnamaldehyde were 0.025 mg/mL and 0.1 mg/mL, respectively, and the MIC and MFC of cinnamic acid were 0.1 mg/mL and 0.4 mg/mL, respectively. Compared to the control group, the treated fungi had a low spore germination rate, distorted, swollen, and broken mycelia, elevated cell membrane permeability, reduced soluble sugar and protein content, and reduced activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH). The experimental results indicated that cinnamaldehyde and cinnamic acid could inhibit spore germination and mycelial growth in Penicillium italicum, damage the cell membrane to increase permeability, facilitate leakage of intracellular contents, interrupt the tricarboxylic acid cycle (TCA) process, and block the energy-generating metabolic pathways, thus inhibiting the growth and development of mycelia．
