Preliminary investigation on the presence of peptidesinhibiting the growth of Listeria innocua and Listeriamonocytogenes in Asiago d’Allevo cheese

Bacteriocins produced by some strains of lactic acid bacteria or antimicrobial casein fragments can be released into the water-soluble fraction of cheeses during ripening. However, there is a lack of experimental evidence which supports the theory that these peptides can exert an effective antimicrobial effect. The aim of this study was to investigate the anti-listerial activity of such peptides in Asiago d’Allevo cheese. The water-soluble fraction of Asiago was ultrafiltrated through 10 kDa cutoff membranes before being dialyzed (100–500 Da cut-off) to remove proteins, salts, and organic acids, prior to freeze-drying. The growth of Listeria innocua LRGIA 01 and of Listeria monocytogenes strain 162 in Brain Heart Infusion (BHI) at 30 °C in the presence or absence of 5 to 40 mg⋅mL−1 of cheese water-soluble extracts (WSEs) lyophilisate was monitored spectrophotometrically. WSEs lyophilisates from cheeses of different production systems (total mixed-ration-fed cows and cheese-making in a dairy plant in May; alpine-grazing cows and cheese-making in situ in July and September) and ripened for 6, 12, and 18 months were tested. A limited dosedependent inhibition of growth was observed at all the assayed concentrations. The addition of cheese WSEs lyophilisates to BHI broth inhibited the growth of <50% of L. innocua LRGIA 01 and <10% of L. monocytogenes strain 162. Antilisterial activity was only significantly affected by ripening time (it was maximal at 6 months). Quantification of peptides with a sequence similar to the antimicrobial casein fragments αS1-CN f(1–23) (isracidin) and αS2-CN f(183–207) in cheese WSEs suggests that their anti-listerial activity is likely also to be due to other peptides.