The antimicrobial and antibiofilm activities of pomegranate peel phenolic compounds against foodborne pathogenic bacteria

Punica granatum L. (pomegranate) is one of the medicinal plants rich in phenolic compounds that possess myriads of pharmacological activities such as anti-inflammatory, anti-tumor, anti-diabetic, nd other effects. High concentrations of these compounds are found in the peel, which constitutes about 50% of the whole fresh fruit. These bioactive phytochemicals have been shown to exhibit a broad spectrum of antimicrobial effects against both Gram-negative and Gram-positive bacteria and fungi. In the present study, the chemical composition, antimicrobial and antibiofilm activities of pomegranate peel extracts (PPE) from seven different varieties were evaluated. Polar phenols, flavonoids, condensed tannins, and anthocyanin contents were quantitatively evaluated. The antimicrobial and antibiofilm activities of each PPE were further tested in vitro against Staphylococcusaureus, Listeria monocytogenes, Salmonella bongori, Escherichia coli, Lacticaseibacillus casei Shirota, and Limosilactobacillus reuteri. Results showed that Gram-positive species were more sensitive than Gram-negative to the extracts tested. In addition, among the tested PPEs three showed high antimicrobial activities at concentrations that varied from 0.09 to 0.75 mg mL-1, with biofilm activity being reduced by more than 70%. These activities were positively related to the punicalagin, flavonoid, and chlorogenicacid content of the extracts. Finally, regarding the pro-technological bacterial strains, they showed very low or no sensitivity to high concentrations of the specific PPEs used. This study proposes a formulation of pomegranate peel extract that valorizes agro-industrial waste in the context of sustainability and circular economy, as well as a potential source of natural, plant-derived antimicrobials, providing an alternative to artificial antimicrobial products.