Growth potential of Listeria monocytogenes in probiotic cottage cheese formulations with reduced sodium content

• Growth of Listeria monocytogenes in probiotic reduced-sodium cottage cheeses (PRSC) was studied.
• Six formulations of PRSC containing different combinations of NaCl, KCl and MgCl2 were studied.
• Salt types/concentrations in cottage cheeses affected the survival of probiotics.
• L. monocytogenes growth was affected by salts depending on the storage conditions.

In this study the growth potential (δ) of Listeria monocytogenes in six formulations of probiotic (Lactobacillus acidophilus and Bifidobacterium lactis) reduced-sodium cottage cheese containing or not NaCl, combined with KCl and/or MgCl2 stored under different temperature conditions was assessed. Reduced-sodium cottage cheeses were inoculated with L. monocytogenes (approximately 103 CFU/g) and then stored at 4 °C (I), 30% of the shelf life at 4 °C and the remaining 70% at 12 °C (II) and 12 °C (III) for 28 days. A growth potential (δ) above 0.5 log CFU/g indicated that the formulation was capable of supporting the growth of L. monocytogenes. The growth potential (δ) of L. monocytogenes at 4 °C (I) was between 0.5 and 0.8 log CFU/g. Higher growth potentials (1.1–1.6 log CFU/g) were observed when the cottage cheeses were stored for 30% of the shelf life at 4 °C followed by storage for 70% at 12 °C (II). In the scenario III (28 days at 12 °C), L. monocytogenes was only able to grow in the formulation with 100% NaCl and no probiotics (F1), while in F2–F6 (probiotic formulations with different combinations of NaCl, KCl, MgCl2) the populations of this bacterium were below the quantification level (< 1 log CFU/g). Independent of the storage scenarios studied, strict conditions of hygiene during processing and use of raw materials of excellent microbiological quality are key-factors for ensuring the safety of this product as L. monocytogenes will be able to grow at low storage temperature.