Temperatures in domestic refrigerators: an important parameter to consider in shelf-life studies

Listeria monocytogenes (Lm) is a pathogenic bacteria able to grow at refrigerated temperatures, widely distributed in the environment and thus susceptible to contaminate various food products of which Ready To Eat (RTE) foods are a particular high-risk category.

Regulation (CE) 2073/2005 defines food safety criterion for Lm in RTE foods. To comply with these criterion, food business operators (FBOs) could conduct studies to evaluate the growth of Lm during shelf-life under reasonably foreseeable storage conditions.

Thus having knowledge of the temperature of domestic refrigerators (last part of the cold chain of refrigerated products) is a key factor for ensuring food safety.

The goal of this study was to gather available data on domestic refrigerator temperatures and to update the European Technical Guidelines for assessing shelf-life of RTE foods related to Lm.

For this purpose, the European Union Reference Laboratory for Lm launched an inquiry in 2019 to National Reference Laboratories in order to collect data from national surveys or studies conducted on domestic refrigerator temperatures in the EU. In parallel, a review of scientific literature published from 2002 to 2020 was performed.

The 75^th and 95^th percentiles of refrigerator temperatures were determined from raw data using R software, obtained directly from the person in charge of the study, estimated from graphical representations of the temperature’s distribution or calculated using numerous simulations based on a normal distribution of the temperatures (mean and standard deviation).

Data collected from nine national surveys and sixteen scientific publications, show that in EU, domestic refrigerators operate with a mean of 6.2°C and that the mean of the 75^th and 95^th percentiles were respectively 7.6°C and 9.8°C.

Based on these outcomes, the temperature at consumer level integrated in the EURL Lm Technical Guidance Document on challenge tests and durability studies for assessing shelf-life of ready-to-eat foods related to Listeria monocytogenes was revised and decreased from 12°C to 10°C.