Purpose: The aim of this study was to evaluate the growth capacity of L. monocytogenes in brain heart infusion agar (BHIA), considered as a simulated cured meat system, with different awvalues.
Methods: A factorial design consisting on the addition of different concentrations of glycerol (0, 5.0, 10.0, 15.0, 20.0 % v/v) and NaCl salt (0, 2.5, 5.0, 7.5, 10.0 % w/v) to BHIA was conducted in order to adjust the aw values. The culture mediums prepared according to the factorial design were pour plated in petri dishes previously inoculated with one ml of a four-strain L. monocytogenes cocktail at a concentration of nearly 10 CFU/ml. The plates were incubated at 37°C and the incubation time varied according to the lag phase observed in each case. The number of cells were determined by count in plate methodology.
Results: The aw values of BHIA ranged from 0.99 to 0.83 and decreased with the increase in salt and glycerol concentrations. In general, L. monocytogenes was able to grow in BHIA with aw values higher than 0.92. The lag time increased with the increase in salt and glycerol concentrations, varying between 24 and 96 h. Salt concentrations higher than 7.5% did not allow L. monocytogenes growth probably due to cells osmotic stress. In BHIA plates with 20% of glycerol, growth was verified only when salt was not added.
Significance: The data presented in this study may help to stablish and evaluate the growth/no growth boundaries of L. monocytogenes in agar simulating meat systems, as a function of aw and salt concentrations.