Influence of Zn2 + , Sodium Bicarbonate, and Citric Acid on the Antibacterial Activity of Ovotransferrin against E. coli O157:H7 and L. monocytogenes in Model Systems and Ham

The antibacterial activity of natural apo-ovotransferrin against E. coli O157:H7 and L. monocytogenes in model systems increased as the concentration of sodium bicarbonate increased. NaHCO3 at 100 mM markedly increased antibacterial activity of ovotransferrin against E. coli O157:H7 and L. monocytogenes. Citric acid at 0.5% enhanced antibacterial activity of apo-ovotransferrin against E. coli O157:H7, but 0.5% citric acid alone also showed a strong bactericidal activity against L. monocytogenes. Addition of NaHCO3 negated the strong antibacterial activity of ovotransferrin plus citric acid against the two pathogens. The antimicrobial activity of ovotransferrin was greatly enhanced by acidic pH conditions. Zn-bound ovotransferrin produced a bacteriostatic effect against L. monocytogenes, but Fe-bound ovotransferrin had little or no antibacterial activity against E. coli O157:H7 and L. monocytogenes. Considering these results, iron bind capacity of ovotransferrin is not the major cause of antibacterial action of ovotransferrin. Previous studies indicate that ovotransferrin directly interacts with bacterial membranes causing a variety of physiochemical changes which affect the survival of microorganisms. Ovotransferrin plus 100 mM NaHCO3 did not exhibit any antibacterial activity against two pathogens in commercial hams, whereas ovotransferrin + 0.5% citric acid suppressed L. monocytogenes in irradiated hams but not in non-irradiated hams. There are some limitations of using ovotransferrin to control pathogens in meat or meat products. To overcome these problems, further studies are needed to determine the mechanisms of antibacterial activity of ovotransferrin and to identify various factors that can improve the antibacterial activity of ovotransferrin.