Partial characterisation of peptides inhibiting Listeria growth in two Alpine cheeses

Listeria monocytogenes, agent of food-borne listeriosis, is a major concern in dairy industry. The aim of this study was to assess the occurrence of peptides inhibiting Listeria spp. growth in two traditional Alpine pressed-curd cheeses: Emmental de Savoie and Asiago d’Allevo, and to get further insights regarding the characteristics of these peptides. Water-soluble extracts of these two cheeses were ultrafiltered onto 10,000-g.mol−1 cut-off filters to remove proteins and the corresponding filtrate was subsequently dialysed with 100–500-g.mol−1 cut-off membranes to remove salt and organic acids. A decrease from 53±2% to 68±1% of Listeria innocua LRGIA01 cells growth after 12-h incubation at 30 °C was observed in the presence of lyophilised extracts of the four cheese samples which were analysed. A less pronounced inhibition of L. monocytogenes 162 strain cells growth by cheese extracts was observed under the same conditions. After ultrafiltration onto 1,000 g.mol−1 cut-off membranes, all the extracts had almost the same anti-L. innocua activity, suggesting that most of antibacterial peptides had a molecularmass between 100–500 and 1,000 g.mol−1. The assay of the anti-L. innocua activity of fractions of Asiago cheese extracts separated by cation-exchange chromatography indicated that non-cationic peptides had a lower antibacterial activity. Taken together, these data suggest that most of antibacterial peptides present in Asiago cheese are low molecular mass and cationic peptides. A significant contribution of intact bacteriocins is thus unlikely; a contribution of either antimicrobial fragments of bacteriocins or caseins released by proteolytic enzymes during cheese ripening is more likely.