• bactericidal activity;
  • dietary supplements;
  • olive;
  • oregano;
  • tea


We evaluated the relative bactericidal activities (BA50) of 10 presumed health-promoting food-based powders (nutraceuticals) and, for comparison, selected known components against the following foodborne pathogens: Escherichia coli O157:H7, Salmonella enterica, Listeria monocytogenes, and Staphylococcus aureus. The relative activities were evaluated using quantitative bactericidal activity [(BA50 value, defined as the percentage of the sample in the assay mixture that resulted in a 50% decrease in colony forming units]. The BA50 values were determined by fitting the data to a sigmoidal curve by regression analysis using concentration–antimicrobial response data. Antimicrobial activity is indicated by a low BA50 value; meaning less material is needed to kill 50% of the bacteria. Olive pomace, olive juice powder, and oregano leaves were active against all 4 pathogens, suggesting that they behave as broad-spectrum antimicrobials. All powders exhibited strong antimicrobial activity against S. aureus. The following powders showed exceptionally high activity against S. aureus (as indicated by the low BA50 values shown in parentheses): apple skin extract (0.002%); olive pomace (0.008%); and grape seed extract (0.016%). Listeria bacteria were also highly susceptible to apple skin extract (0.007%). The most active substances provide candidates for the evaluation of antimicrobial effectiveness in human food and animal feed.

Practical Application: Plant-derived health-promoting food supplements, high in bioactive compounds, are candidates for use as antimicrobials in food.