Effect of NaCl and KCl on fate and growth/no growth interfaces of Listeria monocytogenes Scott A at different pH and nisin concentrations

Abstract

Aims: The fate of Listeria monocytogenes Scott A, was studied in broth, at different aws (by adding NaCl or KCl from 0·0 to 1·4 mol l−1), pHs (from 4·0 to 7·3 by adding lactic acid), and nisin concentrations (from 0 to 100 IU ml−1). Methods and results: Increasing salt and nisin concentrations and decreasing pH resulted in lower growth rates and extended lag phases. At pH 4·5 no growth was observed while in presence of nisin and/or 1 mol l−1 salts of both kinds, L. monocytogenes Scott A was inactivated. Equal‐molar concentrations of NaCl or KCl (similar aw), exerted similar effects against L. monocytogenes in terms of lag phase duration, growth or death rate. The growth boundaries of L. monocytogenes Scott A at 5°C were also estimated by growth/no growth turbidity data, modeled by logistic polynomial regression. The concordance of logistic models, were 99·6 and 99·8% for NaCl and KCl, respectively. Conclusions: The growth interfaces derived by both NaCl and KCl models were almost identical. Hence, NaCl can be replaced by KCl without risking the microbiological safety of the product. Increasing nisin concentrations markedly affected the interface resulting in a more inhibitory environment for L. monocytogenes Scott A. Low to medium salt concentrations (0·3–0·7 mol l−1 of either NaCl or KCl) provided a protective effect against inhibition of L. monocytogenes Scott A by nisin. Significance and impact of the study: Modelling the growth boundaries not only contributes to the development of safer food by providing useful data, but can also be used to study interactions between factors affecting initiation of growth of pathogenic micro‐organisms.

Salt: A Review of its Role in Food Science and Public Health

“…An equivalent reduction in a w to that achievable by salt addition was obtained by addition of KCl. A range from 0 to 1.4mol NaCl and KCl was added and in both cases a w was reduced from 0.999 to ~0.950 [26]. Other salt replacers used include other potassium salts, calcium chloride, magnesium sulphate and metal ions [71].…”

“…In food, L. monocytogenes is capable of growing in cabbage juice containing 5% salt [24], survival was detected in a 30% brine solution stored for > 60 days and in beef immersed in a 22% salt solution stored for 100 days [25]. Lowering a w of the growth media by the addition of salt creates an unfavourable environment for L. monocytogenes, which leads to reduced growth rates, extended lag phases and overall population decline [26]. Growth of L. monocytogenes has been observed at a w of 0.90 in TSB with added salt, and survival has been reported at an a w of 0.83 [25].…”

The effect of nisin and garlic (Allium sativum L.) essential oil separately and in combination on the growth of Listeria monocytogenes

“…This Gram-positive pathogen has the ability to survive under a wide range of conditions such as refrigeration temperatures (2e4 C), acidic pH and high salt concentrations (up to 10 g/100 g) in foods (Gandhi & Chikindas, 2007). Control of L. monocytogenes in various foods usually includes the application of 'hurdle' technology by combining factors such as low temperature, acidification, low a w and chemical or natural preservatives (Boziaris, Skandamis, Anastasiadi, & Nychas, 2006;Hill, Cotter, Sleator, & Gahan, 2002;Valero et al, 2006).…”

The Effect of Thawing and Storage Temperature on the Microbial Quality of Commercial Frozen Ready Meals and Experimental Reduced Salt Frozen Ready Meals

“…The use of salt as a method for food preservation has been well established (Desmond, 2006;Guinee & Fox, 2004). Boziaris et al, (2007) found that salt had a slightly inhibitory affect on bacteria especially at initial exposure but after adaptation, salt may actually stimulate bacterial growth. In contrast to the noted salt tolerance of Listeria spp, Conner et al, (1986) found that cabbage juice containing 1% salt caused an initial decrease in populations of Listeria.…”