Modeling the combined effect of NaCl and pH against Cronobacter spp. using response surface methodology

The growth response of Cronobacter spp. to different levels of NaCl and pH was investigated using response surface methodology. Brain heart infusion (BHI) broth containing 0 to 10% (w/v) NaCl at pH values of 4.5 to 8.0 was inoculated with a cocktail of 5 Cronobacter spp. The mixtures were incubated at 37°C and were sampled at intervals of 0, 2, 4, 6, 8, and 24 hr. Cronobacter spp. were recovered on tryptose soy agar and response surface methodology was employed to investigate the effect of NaCl, pH or their combination on growth and viability. At pH ≤ 5.0, the viability of Cronobacter spp.was reduced below the detection limit after 4 h. In addition, ≥6% NaCl significantly affected Cronobacter spp. growth. However, the interactive effects of pH at 5.5 and 2 to 4% NaCl reduced Cronobacter growth. The response surface analysis indicated that combining NaCl with pH would cause a significantly greater reduction in Cronobacter viability than would be caused by each factor alone. These results showed that Cronobacter may be controlled in food products by concentrations of NaCl ≤4% at pH values ≤5.5. Practical applications: Cronobacter spp. have been isolated from a wide range of foods including cheese, meat, grains, herbs, spices, fermented bread, tofu, infant foods, and fermented beverages Cronobacter spp. have a remarkable ability to survive under a variety of environmental stresses including those involving low water activity (a_w), acidic pH, osmotic challenge, and mild heating. In the current study, the results showed that the growth of Cronobacter in food products could be controlled by the combined effect of NaCl and pH at concentrations of NaCl ≤ 4% at pH values ≤ 5.5.