Background

In September of 2004, Helps et al. (2004) indicated that a common, commercial beef carcass splitting saw (Jarvis Buster VI, Middletown, CN) provides potential for cross-contamination of beef carcasses with potentially infectious tissue. They determined that debris (CNS tissue) remain inside saws despite attempts to sanitize them between splitting differing carcasses during operation. Consumption of CNS tissue infected with Bovine Spongiform Encephalopathy (BSE) has been linked with variant Creutzfeldt-Jakob Disease (vCJD) in humans (Williams, 1997). Additionally, the USDA Food Safety Inspection Service (FSIS), in an Interim Final Rule issued January 12, 2004, designated tonsils and the small intestine (from all cattle) and the spinal cord, brain, trigeminal ganglia, eyes, skull, and dorsal root ganglia (of animals over 30 months of age)as Specified Risk Material (SRM) and prohibited them from entering the human food chain. Cross-contamination with CNS tissue via the splitting saw without further process interventions could result in a food safety threat. Immunochemical methods to detect presence of CNS tissue in or on meat products have been developed (Schmidt et al., 1999, 2001; Hossner et al., 2004). The favored method uses a fluorometric enzyme-linked immunosorbent assay (f-ELISA) for the detection of glial fibrillary acidic protein (GFAP). Glial fibrillary acidic protein is the major protein constituent of glial filaments in differentiated astrocytes which are restricted to the CNS (Eng and Lee, 1995). The efficacy of the GFAP f-ELISA was examined for detection of CNS tissue in blood and muscle from beef cattle (Schmidt et al., 1999, 2001); the GFAP f-ELISA proved to be a simple, cost effective, safe and efficient method to detect minute quantities of CNS tissue in non-neural tissues of beef. 

The objectives of the study were to determine the effectiveness of commercial spray washing systems to remove central nervous system tissue (CNS) from beef carcasses.

Methodology

Carcass Sampling
Using a 100 cm2 template, carcass samples were collected from the aitch bone and the 4th thoracic vertebra, following carcass splitting but before the carcasses were subjected to final spray washing and rinsing intervention cabinets, at each of the five commercial processing facilities (n=50/plant). Samples (N = 250) were collected from one side of each carcass on the slaughter floor and from the opposite side of the same carcass following final carcass washing systems at each plant. All sampled carcasses were designated as being less than 30 months of age and, therefore, did not actually pose a human food-safety threat when CNS tissue contamination was detected. The aitch bone and 4th thoracic vertebra of the lead side of 50 carcasses in each commercial packing plant were sampled using a cotton swab following carcass splitting. A 100 cm2 template was positioned with the dorsal part of the aitch bone in the center of the template, and sampling was done by making 10 horizontal and 10 vertical passes inside the template with one cotton swab. (One pass is one up and down or side to side motion of the swab.) Individual swab samples were immediately placed into 12 x 75 mm polypropylene tubes and capped. After sampling on the slaughter floor, the opposite side of each swabbed carcass was tagged for identification and swab-sampled following each facility’s final carcass wash cabinet, using the procedure described above. All samples were sent, on ice, overnight to Food Safety Net Services, San Antonio, TX (FSNS) for analysis by the GFAP f-ELISA. 

Sampling on the vertebral column utilized a 100 cm2 template positioned with the 4th thoracic vertebra in the top left corner of the template. Sampling occurred by making 10 horizontal and 10 vertical passes inside the template with one cotton swab (one pass is one up and down or side to side motion of the swab). Individual swab samples were immediately placed into 12 x 75 mm polypropylene tubes and capped. After sampling on the slaughter floor, the opposite side of each swabbed carcass was tagged for identification and swab-sampled following each facility’s final carcass wash cabinet using the procedure described above. All samples were sent, on ice, overnight to Food Safety Net Services, San Antonio, TX (FSNS) for analysis. All samples were analyzed using the GFAP f-ELISA protocol outlined in Schmidt et al. (2001) with the following modifications: samples were agitated in an up/down motion 10-15 times in the sample buffer and, A 320 nm excitation filter was used instead of a 360 nm filter to read plates, as it was found to be more appropriate for this assay.

Findings

To determine the efficacy of commercial carcass wash cabinets, 100cm2 samples were collected from the aitch bone and 4th thoracic vertebra of specific carcasses before and after the final carcass wash at five commercial beef packing facilities. Samples were collected from the aitch bone because previous research (Bowling et al., 2004) has shown that some GFAP material present on the aitch bone was a result of cross-contamination from the carcass splitting saw. Samples were collected from the 4th thoracic vertebra to determine if carcass wash cabinets rinse away GFAP material not removed during the slaughter process. The mean (ng/100cm2) GFAP levels for samples collected from the aitch bone and 4th thoracic vertebra before and after the final carcass washing cabinet combined over the five facilities tested are presented in table 1. Mean (ng/100cm2) GFAP levels increased on the aitch bone (P < 0.05), while mean (ng/100cm2) GFAP levels decreased on the 4th thoracic vertebra (P < 0.05). Carcass washing systems in each facility differed in their ability to reduce GFAP on the aitch bone and 4th thoracic vertebra. 

Aitch Bone Sampling
The aitch bones of carcasses sampled in five commercial beef packing facilities showed low or no GFAP contamination (Table 2). This was expected because GFAP present on the aitch bone is cross-contaminated from the carcass splitting saw. The numbers of GFAP f-ELISA positive samples on the aitch bone from each facility before and after each facility’s final carcass wash system are presented in Table 2. Plant A had no GFAP positive samples on the aitch bone before or after their final carcass wash system. Samples from Plants B and E had a numerical (P > 0.05) decrease in GFAP positive samples on the aitch bone after their final carcass washes. Plants C and D had a numerical increase (P > 0.05) in the number of GFAP positive samples on the aitch bone after their carcass washes (Table 2). Mean GFAP levels on the aitch bone increased (P < 0.05) in Plants C and D after their final carcass wash (Table 3). Plant E had a decrease (P = 0.508) in GFAP concentration on the aitch bone after their final carcass wash. There was no change in GFAP concentration on the aitchbone after the final carcass wash at Plant A (Table 3). At plants A, B, D, and E, there were significantly lower levels of residual GFAP on the aitch bone after final carcass washing than was present on finally washed carcasses at Plant C (Table 3). 

4th Thoracic Vertebra Sampling 
The 4th thoracic vertebra was more highly contaminated with GFAP than the aitch bones of carcasses in the five facilities tested. This high level of contamination was expected because the splitting saw contaminates the carcass with its own spinal cord during the splitting process. Plant A had a numerical (P > 0.05) reduction in the number of GFAP f-ELISA positive samples on the 4th thoracic vertebra following final carcass wash while Plant B had a reduction (P = < 0.05) in the number of GFAP positive samples on the 4th thoracic vertebra after their final carcass wash (Table 4). Plants C and E had an increase (P > 0.05) in GFAP positive samples on the 4th thoracic vertebra after their final carcass wash (Table 4). Plant D had no change in the number of positives on the 4th thoracic vertebra after their final carcass wash (Table 4). Plants A, B, and D had a significant (P < 0.05) reduction in GFAP (ng/100cm2) on the 4th thoracic vertebra after their final carcass wash (Table 5). Plant C had a numerical reduction in GFAP levels on the 4th thoracic vertebra after their final carcass wash (Table 5). Plant E had a numerical increase (P < 0.05) in GFAP levels on the 4th thoracic vertebra after their final carcass wash (Table 5). Plant D had a lower (P < 0.05) level of residual GFAP on the 4th thoracic vertebra than Plant C following final carcass washes at each facility (Table 5). All other plants showed only numerical differences in residual GFAP on the 4th thoracic vertebra after their final carcass washes (Table 5). A description of each facility’s final carcass wash system is presented in Table 6.

Implications

In this study, only 6% of samples tested positive for GFAP on the aitch bone; whereas, a higher level of GFAP contamination (69%) was found on the vertebral column. This higher level of GFAP contamination on the vertebral column was expected because the carcass splitting process redistributes GFAP material, unique to the carcass being split, on the vertebral column. Samples were collected from the 4th thoracic vertebra to determine if carcass wash cabinets rinse away GFAP material not removed during the slaughter process. GFAP levels on the 4th thoracic vertebra were significantly reduced (P < 0.05) by final carcass wash cabinets in 3 of 5 plants. GFAP positive samples on the aitch bone were reduced in 2 of five plants and were zero both before and after in one plant.