Inhibition of Listeria monocytogenes and Salmonella by Combinations of Oriental Mustard, Malic Acid, and EDTA

The antimicrobial activities of oriental mustard extract alone or combined with malic acid and EDTA were investigated against Salmonella spp. or Listeria monocytogenes at different temperatures. Five strain Salmonella or L. monocytogenes cocktails were separately inoculated in Brain Heart Infusion broth containing 0.5% (w/v) aqueous oriental mustard extract and incubated at 4 degrees C to 21 degrees C for 21 d. For inhibitor combination tests, Salmonella Typhimurium 02:8423 and L. monocytogenes 2-243 were individually inoculated in Mueller Hinton broth containing the mustard extract with either or both 0.2% (w/v) malic acid and 0.2% (w/v) EDTA and incubated at 10 degrees C or 21 degrees C for 10 to 14 d. Mustard extract inhibited growth of the L. monocytogenes cocktail at 4 degrees C up to 21 d (2.3 log(10) CFU/mL inhibition) or at 10 degrees C for 7 d (2.4 log(10) CFU/mL inhibition). Salmonella spp. viability was slightly, but significantly reduced by mustard extract at 4 degrees C by 21 d. Although hydrolysis of sinigrin in mustard extract by both pathogens was 2 to 6 times higher at 21 degrees C than at 4 degrees C to 10 degrees C, mustard was not inhibitory at 21 degrees C, perhaps because of the instability of its hydrolysis product (allyl isothiocyanate). At 21 degrees C, additive inhibitory effects of mustard extract with EDTA or malic acid led to undetectable levels of S. Typhimurium and L. monocytogenes by 7 d and 10 d, respectively. At 10 degrees C, S. Typhimurium was similarly susceptible, but combinations of antimicrobials were not more inhibitory to L. monocytogenes than the individual agents. Practical Application The bactericidal effects of oriental mustard plus EDTA against Salmonella Typhimurium at 21 degrees C or 10 degrees C and mustard plus malic acid against Listeria monocytogenes at 21 degrees C observed during in vitro tests may be of value in formulating foods to reduce the risk associated with these foodborne pathogens.