Microbial effect of steam vacuum pasteurisation implemented after slaughtering and dressing of sheep and lamb

• We assessed the effect of steam vacuum pasteurisation on microbial contamination of ovine carcasses.
• We investigated the effect of tryptone soy agar (TSA) for resuscitation of Enterobacteriaceae after steam vacuum pasteurisation.
• Steam vacuum pasteurisation on the surface of ovine carcasses is efficient in reducing the microbial number.
• 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 carcass 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 > 82 °C for a duration of 10 s on sheep and lamb carcasses (n = 120). 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 significant for all of the three microorganisms (p < 0.05). For 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% of the figures ranging from a 0.24 to 1.62 log10 CFU/cm2 reduction and a 10–90% range of 0–2.1. The number of positive carcasses with Enterobacteriaceae after steam vacuum pasteurisation was higher in samples where TSA + violet red bile glucose agar (VRBGA) was used compared to samples where only VRBGA was used (p < 0.01). Steam vacuum pasteurisation was found efficient in reducing the total count, read as TPC, as well as the level of E. coli and Enterobacteriaceae.