Hygienic processing: Red meat
Hygienic processing: Red meat
Friday, 10 April 2009
Spray washing was originally introduced in the UK as a method of removing visible dirt from carcasses following the abolition of the wiping cloth in 1968. Concern by meat processors that contact with water would damage both the “bloom” and the keeping quality of carcasses led to the MRI undertaking trials to develop an effective system of spray washing. Initial trials investigated the effect of spray washing on beef and lamb carcasses (Bryce Jones, 1969). This study concluded that there the greatest problems would be presented by lamb carcasses because of the high level of contamination of the fleece. Subsequent trials studied the effect of spray washing on lamb carcasses (Bailey, 1971; 1972).
The results showed that hot water sprays were more effective than cold, though overall bacterial counts were not significantly reduced by any of the regimes studied (<1 log reduction). Hot water imparted a slight “milkiness” initially to the surface of the carcass, which diminished on cooling and was virtually undetectable after 24 h. The trials led to the following optimal specifications:
Spray type: Fan jet system
Dynamic line pressure: 690 kNm-2
Surface impact: 1.035 kNm-2
Water supply temperature: 90°C
Surface spray temperature: 60°C
Water flow rate: 8.5 litres/minute
Though the MRI system was adopted by many abattoirs, concern about the keeping quality of spray washed lamb carcasses continued. Subsequent investigations by Bailey & Roberts in 1976 found a wide range of spray washing systems in place in abattoirs, all bearing little resemblance to the MRI specification. Comparisons between lamb carcasses treated using the MRI system and those systems used by the commercial abattoirs found those systems in commercial use to be inferior to the MRI system.
Final trials in a commercial abattoir between the existing procedure and the MRI system, produced carcasses in both cases that were acceptable after 11 days, with the possible exception of the diaphragm area (that could be trimmed before sale). It was concluded that the commercial storage life of lamb carcasses washed with the MRI system was adequate, i.e. 10 days at 2 to 4°C. The Revised Slaughter House (Hygiene) Regulations 1977 extended the legislation banning wiping cloths to prevent carcass wiping in any form (MLC, 1978). Hudson (1985) reported in the 1980s that commercial abattoirs continued to use ineffective spraying systems.
While work continued in the US and Australia looking at automated washing cabinets and chemical washes little work was carried out in the UK. Decontamination studies at Langford started again in earnest following a comprehensive review of the state of the art for MAFF in 1995 carried out by Stephen James and Christian James (James & James, 1995). This review at the time recommended work on hot water, steam and organic acids. In 1998 FRPERC were commissioned to carry out a further review of microbial contamination and control measures in UK red meat abattoirs for MAFF (James, Nicolaon & James, 1999). This report together with the earlier review on meat decontamination has formed the basis of much of the research programme at FRPERC on red meat control measures.
Initial studies looked at treating a variety of foodstuffs using steam at sub-atmospheric pressure and organic acids (James et al., 1998; Evans et al., 1999) as part of separate UK and EU funded projects. It is obvious that many foods are likely to lose some of their desirable organoleptic properties if subjected to steam at 100°C or above. By generating steam under vacuum high rates of heat transfer and surface heating can still be attained whilst limiting surface temperatures. The decontaminating effect of steam under vacuum was investigated on samples of crispy fruit, leafy vegetables, chicken, pork and paté. Since it is critical that all the surfaces of the food receive similar heating treatments, CFD modelling was used to optimise the distribution of steam within the processing vessels. The equipment produced by these projects were used by partners in other European research groups and a variety of other products have been subsequently treated by these partners with FRPERC designed equipment.
Further studies developed atmospheric and pressurised steam systems, which were used to treat beef primals and retail joints (Purnell et al., 2005). Treatments of beef primals to 100 or 120°C showed no significant differences. After 3 weeks of vacuum-packed storage at 0°C, mean aerobic plate count (APC) and Enterobacteriaceae counts for treated primals were approximately 1 log10 cfu cm-2 lower than for un-treated primals. Levels were similar after 6 weeks of vacuum-packed storage. The effects of a second treatment on retail joints cut from treated and un-treated primals that had been stored in vacuum packs for 3 weeks showed TVC and Enterobacteriaceae counts for treated joints were approximately 1 log10 cfu cm-2 lower than for un-treated joints after 4 and 8 days of over-wrapped storage. The results suggest the steam decontamination treatment used can remove small but significant numbers of bacteria from the beef surface.
As well as direct decontamination interventions, joint studies, with our colleges in DFAS, have recently been carried out for the FSA looking at the role of cross-contamination in the lairage (Small et al., 2006; 2007a, b), and we are currently nearing the end of an FSA project to identify novel methods for reducing salmonella contamination during primary pork processing (Wilkin et al., 2007; James et al., 2007; Tinker et al., 2007).
A further recent FSA project, carried out again with DFAS, was to devise a protocol for hygienically producing skin-on singed sheep carcasses (Fisher, Wilkin & Purnell, 2007). There is a demand by certain ethnic consumer groups in the United Kingdom for skin-on, singed carcasses, primarily from older sheep, but their production is illegal under current EU legislation. The most effect protocol was found to be first singeing the carcass, using specially designed gas burner equipment (designed and constructed by FRPERC), followed by pressure washing to clean the carcass and then evisceration. A second heat application, termed ‘toasting’, applied before chilling was then found to significantly reduce Enterobacteriaceae and APC counts on the carcasses. Carcasses produced in this way had significantly lower Enterobacteriaceae and APC counts, before chilling, than conventionally dressed sheep carcasses produced in the same abattoir.