Inactivation and attachment of Listeria monocytogenes on beef muscle treated with lactic acid and selected bacteriocins

Cubical pieces (1 cm) of aseptically obtained beef muscle were treated with lactic acid (2%), nisin (4 X 10(4) IU/ml) and pediocin PO2 (a bacteriocin produced by Pediococcus acidilactici PO2: 3.2 X 10(3) arbitrary units/ml). Treated meat was immersed for 1 min in a cell suspension of a mixture of two strains of Listeria monocytogenes and then stored for 48 h at 4 degrees C. Meat cubes were analyzed immediately after immersion in the cell suspension, then after 1, 24, and 48 h of storage. Count of L. monocytogenes per cube and percentage of attached cells were determined. Data indicated that the antimicrobial agents significantly (p = 0.05) decreased the count of L. monocytogenes during the 48-h storage by 1.7, 1.1, and 0.6 log(10) CFU/6 cm2 of meat surface for lactic acid, nisin, and pediocin PO2 treatments, respectively. Lactic acid on the meat surface had an immediate and also a delayed listericidal action, but bacteriocins only inhibited L. monocytogenes immediately, and had little or no delayed antilisterial effect. The percentage of Listeria cell attached to the beef muscle significantly (p = 0.05) increased in the presence of lactic acid, but the value did not change significantly or slightly decreased in the presence of nisin and pediocin PO2, respectively