Penicillium expansum, as a main postharvest pathogen of fruits, can secrete patulin (PAT), causing fruit decay and health problems. In this study, the antifungal test, SEM (scanning electron microscope) observation, transcriptional profile, PAT biosynthesis, and physiological characters of P. expansum exposed to cinnamaldehyde and citral combination (Cin/Cit) were evaluated. Cin/Cit could inhibit the mycelial growth and spore germination of P. expansum in a dose-dependent manner. Besides, Cin/Cit caused spores and mycelia wrinkled and depressed by SEM observation. Gene expression profiles of P. expansum were conducted by RNA sequencing (RNA-seq) in the presence or absence of Cin/Cit treatment. A total of 1713 differentially expressed genes (DEGs) were obtained, including 793 down-regulated and 920 up-regulated genes. Most of the DEGs participated in the biosynthesis of secondary metabolites, amino acid metabolism, and oxidation-reduction process, etc. Cin/Cit induced the dysfunction of the mitochondrial membrane, causing the potential influence on energy metabolism and reactive oxidative species production. The changes of superoxide dismutase (SOD) and catalase (CAT) activities combing with the increase of hydrogen peroxide content indicated the oxidative stress on P. expansum induced by Cin/Cit, which corresponded well with the transcriptional results. Moreover, both the RNA-seq data and the qRT-PCR showed the remarkable down-regulation of genes included in the PAT biosynthetic pathway under the Cin/Cit treatment. These findings provided more useful information about the antifungal mechanism of Cin/Cit against P. expansum at molecular and gene levels and suggested that Cin/Cit is a potential candidate to control P. expansum.

Extractable and unextractable proanthocyanidins (EPAs and UEPAs) from leaves of bayberry were characterized. Both EPAs and UEPAs were analyzed by acid catalysis in the presence of excess phloroglucinol. The main cleavage product, epigallocatechin-3-O-gallate-(4β→2)-phloroglucinol, was successfully identified. The EPAs were of the prodelphinidin type. In fact, epigallocatechin-3-O-gallate (EGCG) and traces of epigallocatechin (EGC) were detected as the extension units, but only EGCG was present in the terminal units. All of the compounds exhibited a 2,3-cis configuration, and >98% of them were galloylated. The mean degree of polymerization (mDP) of bayberry leaf EPAs was 6.5, and the most abundant EPAs were the polymers, with mDP values of 9.5−26.7. The UEPAs were highly polymerized prodelphinidins consisting of EGCG and traces of EGC. In addition, EGCG, three EPA dimers, and two trimers were identified. The EPAs and UEPAs consisted mostly of EGCG, which is unusual in the plant kingdom.

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Cinnamaldehyde (Cin) and citral (Cit) have been studied as antimicrobial agents and natural preservatives, but their action modes are controversial, and the knowledge of their antifungal mechanism against P. expansum is still incomplete.

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