Short communication Combined antimicrobial activity of reuterin and diacetyl against foodborne pathogens

Abstract

Reuterin (β-hydroxypropionialdehyde) is a broad-spectrum antimicrobial substance produced by some strains of Lactobacillus reuteri during anaerobic fermentation of glycerol. Some of these strains are able to survive and produce reuterin in cheese and yogurt when added as adjuncts to the starter. Similarly, in fermented dairy foods, other inhibitory compounds such as lactic acid and diacetyl are produced during fermentation. In this work, we studied the combined effect of reuterin and diacetyl under different pH conditions against Escherichia coli O157H7, Salmonella Enteritidis, and Listeria monocytogenes. Results from agar spot assays showed that the antimicrobial activity of reuterin-producing strains against the gram-negative bacteria tested was enhanced as the concentration of diacetyl increased to 50. mg/kg, and was higher under acidic conditions (pH 5.0) for the 3 pathogenic strains. The combination of reuterin and diacetyl had an additive effect against L. monocytogenes only at diacetyl concentrations of 50. mg/kg and pH 5.0. In addition, growth kinetics studies showed that the combination of 1 activity unit (AU)/mL of reuterin with 100. mg/kg diacetyl increased the lag time of the 3 pathogens. In milk, synergistic antimicrobial activity was observed with the combination of 1. AU/mL reuterin and 50 or 100. mg/kg of diacetyl on the gram-negative strains tested, and with 1. AU/mL reuterin and 100. mg/kg of diacetyl on L. monocytogenes. The greatest inhibition of the 3 pathogens was achieved in acidified milk at pH 5.0 with reuterin (1. AU/mL) and diacetyl (100. mg/kg). Based on these results, the combination of reuterin and diacetyl in acidified dairy products could be a promising strategy to control food pathogens in these products. © 2014 American Dairy Science Association.