Anti-listeria effect of water-soluble extracts of Asiago cheese

Cheese ripening involves a complex series of biochemical events that leads to the characteristics taste, aroma and texture of each cheese variety. The most complex of these biochemical events, proteolysis, is caused by milk, milk-clotting, starter and secondary flora enzymes. During cheese ripening, peptides generation mainly results from caseinolysis. Some of these peptides are bioactive: they exert biological activities such as immunomodulatory, antithrombotic and antibacterial activities. Asiago is a “Protected Denomination of Origin” (PDO) cheese of the North-Eastern region of Italy produced in two different varieties according to the length of ripening. Asiago d’Allevo is the variety produced with skimmed raw milk and ripened for periods varying from 6 to 18 months. The main goal of this research was to evaluate the presence of antibacterial peptides in Asiago d’Allevo cheese toward two bacterial strains. The samples analysed were produced in alpine farms of Asiago plateau (Vicenza, Italy). The presence of antimicrobial peptides was assessed in water-soluble extracts (WSE) of Asiago cheese ultrafiltrated onto 10 kDa cut-off membranes to remove proteins and dialysed in 100 Da cutoff dialysis bags to remove salt and organic acids. The antimicrobial activity of these WSEs was tested on Listeria innocua first. The samples that presented an inhibition were subsequently tested on Listeria monocytogenes. Antimicrobial activity was assayed by a micro-method using 96-well microplates and a microplate reader to determine microbial growth inhibition.