Effect of Sodium Reduction on Listeria monocytogenes in Mozzarella Cheese Stored at 4 and 12°C

Introduction: Salt (NaCl) is added to foods to help inhibit microbial growth and improve flavor.  However, a diet high in sodium has been associated with high blood pressure, leading to an increased risk for cardiovascular disease and stroke.  While lowering the amount of salt in processed food products could decrease these risks, the microbial stability of reduced sodium products may be altered.  

Purpose: The purpose of this study was to determine the fate of Listeria monocytogenes in artificially inoculated full sodium and low sodium mozzarella cheese stored at 4 and 12ºC.

Methods: Low sodium (0.65% NaCl) and full sodium (1.80% NaCl) Mozzarella cheese were cut into 15 g pieces and inoculated with approximately 2 log CFU/g of a L. monocytogenes cocktail.  The Mozzarella cheese was tested for L. monocytogenes, coliforms, yeast, mold, psychrotrophs, pH and water activity after 0, 1, 7, 15, 35, 60 and 90 d and after 0, 1, 3, 7, 15 and 35 d when stored at 4 and 12°C, respectively.  Counts were compared using ANOVA.

Results: The initial water activities were 0.9854 ± 0.0036 and 0.9796 ± 0.0089 for the low and full sodium Mozzarella cheeses, respectively.  There was no statistical difference (P < 0.05) in the pH or in the recovery of L. monocytogenes, coliforms, yeast, mold or psychrotrophs between the full and low sodium Mozzarella cheese at both 4 and 12°C.  Under all test conditions, L. monocytogenes decreased by an average of 0.62 ± 0.35 log CFU/g at the end of incubation.

Significance: These data suggest that sodium could be reduced in Mozzarella cheese without altering the microbial stability.