Spoilage bacteria grow faster than pathogenic organisms, finds EFSA analysis
EFSA assessed the impact of time and temperature on growth using predictive models to compare spoilage and pathogenic bacteria.
The EFSA Panel on Biological Hazards (BIOHAZ) has already published two scientific opinions on the public health risk related to the maintenance of the cold chain during storage and transport of meat (see related news).
Spoilage bacteria
Pseudomonads and lactic acid bacteria (LAB) are the most relevant organisms for looking at the effect of specific chilling time–temperature scenarios on growth of spoilage bacteria under aerobic and anaerobic (vacuum packs) conditions.
In both cases, a population of 107 CFU/cm2 was considered as the level at which spoilage occurred (end of shelf-life).
A comparison of predicted growth of spoilage bacteria (pseudomonads) with that of pathogens (L. monocytogenes and Y. enterocolitica), suggests the spoilage bacteria grow more rapidly and will limit the target carcass surface temperature and transport time–temperature combinations.
Pseudomonad growth was modelled on beef, pork and lamb carcasses, chilled to target surface temperatures and compared with growth if the carcasses were chilled to a core temperature of 7°C, according to the scientific opinion.
Regulation (EC) No 853/2004 requires that carcasses are immediately chilled after post-mortem inspection to ensure the temperature throughout the meat is not higher than 7°C for meat and not above 3°C for offal but there is no provision on the time limit to achieve this temperature.
Beef and lamb carcasses are usually not chilled to below 10°C (core temperature) within the first ten hours to avoid cold shortening and toughening. Bacteria will grow on the surface of the carcass until the temperature is reduced sufficiently to slow bacterial activity.
Factors affecting meat spoilage include temperature, pH, water activity and storage atmosphere.
Levels of bacterial contamination, including pseudomonads on beef, pork, lamb and poultry carcasses will depend on factors including season, animal/bird cleanliness, abattoir prerequisite activities such as good hygiene practices (GHP) and sampling stage.
Results summary
The results suggest that pseudomonad growth on red meat ranges from 0.4 log10 CFU/cm2 (stored aerobically at 1°C for 1 day) to 9.5 log10 CFU/cm2 (stored aerobically at 7°C for 12 days, assuming the initial concentration was 1 CFU/cm2).
The equivalent values on poultry were 0.8 log10 CFU/cm2 and 9.5 log10 CFU/cm2, respectively.
Predicted LAB growth (under anaerobic conditions) was lower, with the equivalent values of 0.2 log10 CFU/cm2 and 7.8 log10 CFU/cm2, respectively.
The time required for pseudomonads to reach 10 CFU/cm2 on red meat was 15 days when stored at 1°C and the initial count was 1 log10 CFU/cm2 and 7.1 days on poultry. The equivalent time for LAB on red meat stored anaerobically was 35.5 days.
Chilling bovine or ovine carcasses to between 4 and 10°C surface temperature results in similar or lower predicted pseudomonad growth as compared to chilling to a core temperature of 7°C.
Results for porcine carcasses depended on the target surface temperature and chilling curve applied.
Lower initial carcass counts mean greater flexibility in the time–temperature combinations in the abattoir chilling rooms and during transportation, said the panel.
“A slaughterhouse with effective prerequisite programmes (good manufacturing practice (GMP)/GHP) can significantly reduce the contamination with spoilage bacteria and thus carcasses can be transported for longer times, at a given temperature, before spoilage occurs.
“In contrast, lack of hygiene control usually leads to high levels of spoilage bacteria limiting the transportation time before spoilage.”
