Background

Spray-chilling is the intermittent addition of potable water to the surfaces of carcasses during the first stage (initial 8-12 h) of chilling. This process reduces evaporative water losses from carcass surfaces that result in considerable weight shrinkage. Carcass weight loss due to evaporation of water can be reduced by 0.5 to 1.5 % by spray application during the first 24 hours of chilling (Allen et al., 1987; Jones et al., 1988). Although carcass shrink is an important financial factor for the beef industry, scientific research has been conducted (Doyle et al., 2002; Gill et al., 2003; Hippe et al., 1990) to determine if increased water activity on carcass surfaces during chilling has a significant effect on microbial activity. Carcass surface temperature is not the singular, limiting, factor in proliferation of pathogenic bacteria (Doyle et al, 2002). The time required for carcass surfaces to reach a temperature low enough to retard microbial proliferation is also critical, and it is during this window, while surfaces are warm and wet, where it becomes a concern that pathogenic bacterial profiles are being shifted (Cross et al., 2004). 

The microbiological profiles of carcasses exiting the hot box rely heavily on the good manufacturing practices (GMPs) implemented at each individual packing facility, the dedication of its employees and the upkeep of a properly constructed hot box. The final destination of outer surfaces of beef carcasses are often to trimmings destined for ground product, making control of pathogenic bacterial levels on carcasses before and after chilling critical (Schmidt et al., 1998). Multiple intervention hurdles applied before chilling can be nullified by poor hot box GMPs, therefore, it is imperative that a plant implement rigid, yet practical guidelines for the proper handling and storage of carcasses during chilling such as those recommended by Schmidt et al., (1998):

• All overhead surfaces and equipment must be kept free of condensation.
• Stringent regulation of air and water quality.
• Adequate carcass spacing to allow for rapid cooling of entire carcass surface.
• Detours to minimize worker traffic through the hot box should be created.
• All employees and equipment coming in contact with carcass surfaces should sanitize/be sanitized frequently.

Gill (2003) stated that although past research shows little difference between dry-chilling vs. spray-chilling methods, some commercial plants have implemented slower, extended spray-chilling systems to reduce the risk of cold shortening and subsequent decreases in product tenderness. These changes combined with the antimicrobial hurdles being applied at most North American beef processing facilities, could be affecting microbiological integrity of carcasses. Since past research was conducted on carcasses not receiving current antimicrobial intervention strategies (Gill 2003), the effects of microbial decontamination methods and current spray-chilling practices in combination are uncertain and require further investigation (Gill 2003).

The stated objectives for this work were:

• To examine potential introduction of E. coli 0157:H7 to beef carcasses in hotboxes of three commercial plants during chilling.
• To determine the changes in APC, TCC, and ECC and prevalence of E. coli 0157:H7 on beef carcasses chilled using spray-chilling vs. dry-chilling.
• To characterize hot box “best practices” by comparing hot box conditions, carcass handling practices and outcomes in three commercial processing beef packing plants.
• To compare APC, TCC and ECC populations of samples recovered from the upper region of hanging carcasses versus the lower region.

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