Feruloyl-amides as natural antimicrobials for crop and food protection

Background: Plants have developed multiple chemical defence responses against pathogen attacks. The main mechanism of defence is based on a rapid transcriptional reprogramming of genes encoding biosynthetic enzymes that synthesize specific secondary metabolites. Increasing evidence indicates phenylamides (PAs) as an important group of bioactive compounds in food plants. Results: We synthesized a small collection of ferulic acid-derived phenylamides by chemoenzymatic approaches. The compounds were tested against fungal and bacterial pathogens to assess their antimicrobial potential. The treatment with the synthesized phenylamides showed modest inhibition of the fungal growth (up to 25%) and had no significant influence on spore germination, whereas some of the compounds gave a considerable inhibition of Pyricularia oryzae appressorium formation, up to 94%. They also exhibited in vitro antibacterial activity against six foodborne bacterial pathogens. Monitoring of six growth parameters (taking into account growth rate, time and absorbance) measured during 24 h incubation showed that the synthesized molecules, assayed at four concentrations between 12.5 and 100 mg/L, produced a stronger average antimicrobial effect against Gram-positive pathogenic strains than against Gram-negative ones. Conclusions: The obtained results evidenced that the effect of this class of compounds is mainly related to blocking fungal virulence mechanisms, mediated by a significant effect on appressorium maturation, rather than to mycelium growth inhibition. Together with the observed in vitro antibacterial activity against foodborne bacterial pathogens, we conclude that PAs are promising candidates for future developments in the agri-food sector.