Spanish researchers assess shelf life and Listeria risk

Scientists in Spain have assessed the shelf life safety of certain ready-to-eat foods and the risk from Listeria monocytogenes.

The Barcelona Public Health Agency (ASPB) asked for an opinion on the safe shelf life of Listeria monocytogenes in products such as cheeses, cooked meats, including pâtés, and cured meats sliced and prepackaged before retail sale. It was published recently in the Food Risk Assess Europe journal.

In 2019, 72 listeriosis cases were reported in Catalonia. ASPB provided 90 samples (32 in 2020 and 58 in 2021) from four categories of ready-to-eat foods. Food was sliced or cut into portions in retail establishments in Barcelona and packaged in different formats: vacuum-packed, in a heat-sealed or shrink-wrapped tray, or wrapped in film.

The prevalence of Listeria monocytogenes was 6.75 percent, and positive samples were from all food categories. Shiga toxin-producing E. coli (STEC) was also detected in two samples of cheese made from raw milk; one of these was E. coli O145.

Setting a safe shelf life

95 percent of the product display equipment was at temperatures equal to or below 5 degrees C (41 degrees F). Scientists found 44 samples did not include any date on the packaging.

Results showed considerable variability in the growth potential of Listeria monocytogenes due to the different characteristics of the products evaluated.

One scenario assumed an initial concentration of 1 colony forming unit per gram (CFU/g) and storage at 5 degrees C (41 degrees F). In this test, the limit of 100 CFU/g would not be reached during the seven days evaluated. However, in scenarios that include phases at a temperature of 9.5 degrees C (49.1 degrees F), the concentration of the pathogen would exceed 100 CFU/g during or at the end of seven days.

Findings indicated that cheeses, cooked ham, and pâtés required the indication of a use-by date, as handling conditions expose the product to potential Listeria monocytogenes contamination, and the pH and aw (water activity) characteristics of these products support its growth.

In reasonably foreseeable scenarios of temperature abuse by the consumer, the safe shelf life of all product groups evaluated would be less than five days. This was considering storage temperature conditions in retail for two days at 5 degrees C (41 degrees F) and in a domestic refrigerator for five days at 9.5 degrees C (49.1 degrees F).

Scientists said this estimate results from a conservative approach that provides a margin of safety to the evaluation and matches the five days in EU regulation when the operator does not present studies that guarantee a safe, longer shelf life.

Australia meat testing assessment

The European Food Safety Authority (EFSA) has also examined the impact of revising an Australian monitoring program on its ability to detect microbiological contamination. 

In 2010, the European Commission judged the current Australian beef and sheep meat program to be equivalent to EU requirements for microbiological monitoring. In 2021, Australia said it was reforming its meat export system.

The current and proposed programs were described, and the number of alerts was compared using a modeling approach. In the current program, only beef and sheep carcasses are monitored using three‐class moving window sampling plans, while in the planned program, carcass, bulk meat, primal, and offal are checked using four two‐class sampling plans, but Salmonella testing is excluded.

The proposed program leads to an alert when limits in the moving window criteria are exceeded for at least one of the four two-class sampling plans. Previously, any exceedance of limits in the moving window criteria led to an alert, and the establishment was required to take corrective action.

The Salmonella change was made because carcass monitoring data has shown a very low and decreasing prevalence over more than 10 years in Australian production. Salmonella will be monitored in red meat periodically during national baseline surveys. All beef exports to Finland and Sweden will still be checked for Salmonella.

EFSA provided data, including microbial results from 29 beef and 16 sheep slaughterhouses exporting to the EU from October 2017 to November 2022.

Interventions following an alert from APC or E. coli and from Salmonella are different. The latter may extend to the pre-harvest stage of the meat production chain if evidence for poor process hygiene is not identified at harvest level and include a more stringent procedure when alerts are repeated.

Models revealed that the current program provides higher alerts for aerobic plate count (APC), while the proposed setup has more alerts for E. coli. For APC and E. coli, the estimated number of alerts was similar for beef or higher for sheep for the future compared to the current program. This indicates the proposed program performs equivalent or higher in detecting such contamination, said EFSA.

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Source: https://www.foodsafetynews.com/2024/08/researchers-assess-shelf-life-and-listeria-risk/