Listeria survives better at low temperatures in cured and soft cheeses than at room temperature

A study carried out by the University of Cordoba and the University of Burgos to understand the food safety of soft and cured cheeses found that storage at room temperature does not compromise food safety with respect to the presence of Listeria monocytogenes in both types of cheeses, compared to refrigeration, nor does the reduction of salt in soft cheeses in the range studied.

Listeria monocytogenes is a bacterium of great relevance to the food industry, and can pose a problem for the population, as it is the cause of listeriosis, especially in ready-to-eat products that are not subjected to any previous cooking processes. Guaranteeing food safety is key. Therefore, the "Bromatological Hygiene" and "One Health Microbiology" research groups at the University of Cordoba and the University of Burgos, respectively, carried out a study to evaluate two essential factors in the preservation of cheeses - storage temperature and salt regulation - and verify how the pathogen L. monocytogenes behaves.

To study how temperature could affect the behavior of the bacteria in cured and soft cheeses, the two research groups analyzed the products at two different temperatures: one that reflected the refrigeration of the product (4ºC), and the other, its storage at room temperature (22ºC). The results were striking, as the bacteria actually survived better at lower storage temperatures.

Regarding salt concentration, they found that its reduction in soft cheeses, between 1.17% and 0.30%, did not affect the behavior of the microorganism, therefore not compromising the safety of the product with respect to the presence of L. monocytogenes. As the researcher at the University of Cordoba Arícia Possas points out, "this isquite a positive result, taking into account the recommendations of the World Health Organization to reduce salt consumption by 30% by 2025" as a strategy to reduce the risk of cardiovascular disease.

As UCO researcher Antonio Valero explains: "the results are valuable for the food industry, for health authorities, and for the population, in general, as they make it possible to improve labelling and establish, on a scientific basis, the useful life of the products, as well as giving us a tool to verify the control of the manufacturing process." As stated in the article, this is particularly relevant considering that, between 2016 and 2021, 46 alerts were reported on the presence of L. monocytogenes in cheeses produced and distributed in EU countries.

Although the danger of the bacterium still exists, in the event of cross-contamination, for example, the monitoring of good practices in the manufacture of cheeses, adds Valero, makes them safe foods. It must be borne in mind, however, that each type of cheese is different, so the bacteria's behavior can also vary. For example, it is necessary to pay attention to fresh cheeses, where L. monocytogenes could be able to proliferate during storage at room temperature, even reaching high levels if handling and storage conditions are not adequately monitored.

Reference:
Possas A., Hernández M., Esteban-Carbonero Ó., Valero A., Rodríguez-Lázaro D., "Listeria monocytogenes survives better at lower storage temperatures in regular and low-salt soft and cured cheeses", Food Microbiology, Volume 104, June 2022. https://doi.org/10.1016/j.fm.2022.103979.