Antibacterial Effect of Extracts Rich in Tannins Isolated from Berry Waste Against Pathogens Contaminating Food

Background: Microbiological contamination of food and the increasing prevalence of antimicrobial resistance have intensified the search for natural alternatives to conventional preservatives. Berry-processing pomace is a rich source of tannins with recognized antimicrobial potential; however, information on the relationship between tannin composition and activity against foodborne pathogens remains limited. Methods and results: Tannin-rich extracts were isolated from pomace obtained after the processing of raspberry and blackberry (Rubus) as well as strawberry and wild strawberry (Fragaria) fruits using acetone extraction followed by purification with Amberlite XAD 1600 N resin and Size Exclusion Chromatography. The composition of the extracts was characterized by HPLC-DAD-MS QExactive and HPLC-FD. Antibacterial activity against 15 foodborne pathogenic strains belonging to the genera Listeria, Escherichia, Salmonella, and Staphylococcus was evaluated using disk diffusion and minimum inhibitory concentration (MIC) assays, while antibiofilm activity was assessed against Listeria innocua. Eight extracts differing in ellagitannin (10-72 g/100 g) and condensed tannin (4-25 g/100 g) contents were evaluated. All extracts exhibited antibacterial activity, and inhibition zones were positively correlated with ellagitannin content and negatively correlated with procyanidin concentration. For most microorganisms, MIC values ranged from 0.391 to 12.5 mg/mL, with no significant differences between Gram-positive and Gram-negative bacteria, whereas the susceptibility of Listeria monocytogenes depended on the strain and extract type. Furthermore, all extracts significantly reduced L. innocua biofilm formation. Conclusions: Tannin-rich extracts recovered from berry-processing by-products exhibit broad-spectrum antibacterial and antibiofilm activity against foodborne pathogens. The observed relationships between polyphenol composition and antimicrobial efficacy highlight the important role of ellagitannins in antibacterial activity and support the valorization of berry pomace as a sustainable source of natural food-preservation agents.