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Abstract
Aims. This paper compares changes in visible and microbiological contamination on lamb carcasses dressed using one system which includes process factors previously identified as potential critical control points for HACCP-based approaches to hygienic slaughter and dressing, and another system which excludes those factors.
Methods. Longitudinal changes in microbiological and visible contamination of lamb carcasses were quantified in two slaughterhouses, one utilising clean, shorn, unwashed lambs in an inverted dressing system, the other utilising dirty, woolly, washed lambs in a traditional dressing system. Excision samples (5 cm2 each) for microbiological analyses were taken from two sites on 25 carcasses per treatment group immediately after pelting, at the completion of dressing, after overnight chilling and after boning and packaging. Visible contamination on the surface of 300 carcasses per treatment group was assessed after pelting and after overnight chilling.
Results. Mean aerobic plate counts and Escherichia coli counts on the leg and loin in the inverted dressing system were low after pelting (log10/cm2 1.86 and 1.71; log10/cm2 0.13 and 0.05 respectively) but generally showed statistically significant increases through to final packaging. In the conventional dressing system, there were much higher counts on the leg and loin after pelting (log10/cm2 4.66 and 2.71; log10/cm2 2.21 and 0.24 respectively), but subsequent handling of the carcass by slaughterline workers had no measurable deleterious effects. The inverted dressing system resulted in final mean aerobic plate counts on meat at packaging that were 1.38% (leg) and 48.98% (loin) of those derived from the conventional dressing system. Mean E. coli counts from the inverted system were 21.37% (leg) and 67.61% (loin) of those from the conventional system. There was an inverse relationship between the prevalence of carcasses with visible faecal contamination and their microbiological status.
Conclusion. Significant reductions in microbiological contamination of sheep carcasses can be brought about by HACCP-based systems. Possible critical control points are pre-slaughter presentation status (including avoidance of pre-slaughter washing), inverted dressing, handling by slaughterline workers and meat inspectors, and chilling. Use of levels of visual faecal contamination as an on-line monitoring parameter for slaughter hygiene can give erroneous results. Interactions between different process steps may alter the effectiveness of the HACCP plan, and successful design and application depends on a detailed knowledge of the specific process utilised in each slaughterhouse.