Influence of zinc, sodium bicarbonate, and citric acid on the antibacterial activity of ovotransferrin against Escherichia coli O157:H7 and Listeria monocytogenes in model systems and ham.
The influence of NaHCO(3) and citric acid on the antibacterial activity of apo-ovotransferrin in model systems and ham was investigated. The antibacterial activity of 20 mg/mL of ovotransferrin solution with added NaHCO(3) (0, 25, 50, or 100 mM) or citric acid (0.25 or 0.5%) was evaluated against Escherichia coli O157:H7 and Listeria monocytogenes in brain heart infusion broth. The antimicrobial activity of ovotransferrin saturated with Fe(2+) or Zn(2+) against both pathogens was also measured. In addition, ovotransferrin solutions containing either 100 mM NaHCO(3) or 0.5% citric acid were applied to commercial hams inoculated with E. coli O157:H7 or L. monocytogenes and stored at 4 degrees C for 4 wk. The antimicrobial activity of ovotransferrin increased as the concentration of added NaHCO(3) increased. Sodium bicarbonate (100 mM) significantly improved the antibacterial activity of ovotransferrin against E. coli O157:H7 and L. monocytogenes. Citric acid (0.5%) combined with ovotransferrin resulted in a synergistic antibacterial effect against E. coli O157:H7, and L. monocytogenes was susceptible to 0.5% citric acid alone. Sodium bicarbonate diminished the strong antibacterial activity of ovotransferrin + citric acid against E. coli O157:H7, and use of sodium citrate instead of citric acid did not produce any antibacterial activity against the pathogens. The antimicrobial activity of ovotransferrin increased significantly under acidic conditions. The Zn-bound ovotransferrin prevented the growth of L. monocytogenes as detected in the apo-ovotransferrin combined with 100 mM NaHCO(3) treatment, but Fe-bound ovotransferrin had little or no inhibitory activity against E. coli O157:H7 and L. monocytogenes. Ovotransferrin + 100 mM NaHCO(3) did not exhibit any antibacterial activity against the 2 pathogens in commercial hams, whereas ovotransferrin + 0.5% citric acid suppressed the growth of L. monocytogenes in irradiated hams. In conclusion, combinations of ovotransferrin with NaHCO(3), citric acid, or Zn(2+) enhanced the antibacterial activity of ovotransferrin against E. coli and L. monocytogenes, but there are some limitations as discussed for applying ovotransferrin to meat or meat products.
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Department of Animal Science, Iowa State University, Ames 50011, USA.
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D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D019343:Citric Acid / Q000008:administration & dosage / Q000494:pharmacology*; D003207:Conalbumin / Q000494:pharmacology*; D019453:Escherichia coli O157 / Q000187:drug effects*; D005516:Food Microbiology; D007928:Lethal Dose 50; D008089:Listeria monocytogenes / Q000187:drug effects*; D008460:Meat / Q000382:microbiology; D017693:Sodium Bicarbonate / Q000494:pharmacology*; D013552:Swine; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D003207:Conalbumin; D019343:Citric Acid; D017693:Sodium Bicarbonate; D015032:Zinc