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Steam Vacuum Pasteurisation on Sheep Carcases

23 October 2014

Steam vacuum pasteurisation on the surface of sheep and lamb carcases is efficient in reducing the microbial number.

In a study on the microbial effect of steam vacuum pasteurisation implemented after slaughtering and dressing of sheep and lamb the Norwegian research team also investigated the effect of tryptone soy agar (TSA) for resuscitation of Enterobacteriaceae after steam vacuum pasteurisation.

The team of Ammar Ali Hassan, Eystein Skjerve, Claus Bergh and Truls Nesbakken from the Department of Food Safety and Infection Biology, Section for Food Safety in the Faculty of Veterinary Medicine and Biosciences at the Norwegian University of Life Sciences and the Department of Community Medicine in the Faculty of Health Sciences at UiT The Arctic University of Norway showed the use of tryptone soy agar (TSA) is recommended for growth of Enterobacteriaceae that need resuscitation.

The main objective of the study was to assess the effect of steam vacuum pasteurisation on carcase contamination with focus on Escherichia coli, Enterobacteriaceae and total plate count (TPC).

Additionally, the effect of an additional tryptone soy agar (TSA) step for resuscitation of Enterobacteriaceae after steam vacuum pasteurisation was investigated.

Steam vacuum pasteurisation was applied at a temperature of more than 82°C for a duration of 10 seconds on 120 sheep and lamb carcases.

Samples were taken immediately:
i) after trimming just before the use of steam vacuum and
ii) after use of steam vacuum. Nordic Committee on Food Analysis methods were used in microbial analyses.

The differences in log reduction were found to be significant for all of the three microorganisms (p < 0.05).

For the total plate count (TPC), the general reduction was a 0.65 log10 in the number of colony forming units (CFU) per cm2.

For E. coli, the median reduction effect on carcasses positive before decontamination was 1.1 log10 CFU/cm2.

A large variability of the effect was however found, with 50 per cent of the figures ranging from a 0.24 to 1.62 log10 CFU/cm2 reduction and a 10–90 per cent range of 0–2.1.

The number of positive carcases with Enterobacteriaceae after steam vacuum pasteurisation was higher in samples where tryptone soy agar (TSA) + violet red bile glucose agar (VRBGA) was used compared to samples where only VRBGA was used (p < 0.01).

The researchers said that steam vacuum pasteurisation was found efficient in reducing the total count, read as total plate countTPC, as well as the level of E.coli and Enterobacteriaceae.

The study has been published in the January 2015 issue of Meat Science.

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October 2014

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