ABSTRACT
This study evaluated the combined effects of pH, NaCl, incubation temperature, and sublethal concentrations of monolaurin on the survival of Listeria monocytogenes using the double-gradient diffusion technique. L. monocytogenes tolerance to NaCl was greatest (>78 g/liter) at neutral pH (6.8 to 7.2) and increased in the pH range 7.0 to 5.4 as the incubation temperature was lowered. Monolaurin at 2 µg/ml lowered the salt tolerance of L. monocytogenes to 60 g/liter independently of pH. At 4 µg of monolaurin per ml, salt tolerance was reduced to approximately 40 g/liter with no growth occurring at pH 6.0 to 5.4 and 25 g of NaCl per liter. At 8 µg of monolaurin per ml, only a subpopulation of the initial inoculum tolerated 25 g of NaCl per liter at neutral pH (6.5 to 7.5). Monolaurin reduced the tolerance of L. monocytogenes to NaCl and low pH.
