Development and Evaluation of an On-Line Hide Decontamination Procedure for Use in a Commercial Beef Processing Plant†

The hides of cattle are the source of Escherichia coli O157:H7 that contaminates beef carcasses during commercial beef processing. Therefore, effective interventions that reduce hide contamination should reduce subsequent carcass contamination. The first objective of this study was to identify the most effective reagents for decontamination of beef hides. Cattle hides draped over barrels were used for in vitro experiments to compare the efficacy of washes using 1.6% sodium hydroxide, 4% trisodium phosphate, 4% chlorofoam, or 4% phosphoric acid, each followed by a rinse step using either water or acidified (pH 7.0) chlorine at 200 or 500 ppm. All treatments using a water rinse reduced hide coliform counts by 1.5 to 2.5 log CFU/ 100 cm2. Compared with water rinses, 200 and 500 ppm acidified chlorine rinses increased efficacy by approximately 1.0 and 2.0 log CFU/100 cm2, respectively. Vacuuming of the treated areas to remove excess liquid improved hide cleanliness by an average of an additional 1.0 log CFU/100 cm2. The second objective was to evaluate the use of an on-line hide-wash cabinet that used a sodium hydroxide wash and a chlorinated (1 ppm) water rinse. Hides sampled before entering and after exiting the cabinet had aerobic plate counts and Enterobacteriaceae counts that were reduced by 2.1 and 3.4 log CFU/100 cm2, respectively, and the prevalence of E. coli O157 on hides was reduced from 44 to 17% when the cabinet was in use. Preevisceration carcass aerobic plate counts and Enterobacteriaceae counts were both reduced by 0.8 log CFU/100 cm2, and the prevalence of E. coli O157 on preevisceration carcasses was reduced from 17 to 2% when the cabinet was in use. These results support decontamination of hides as an effective means to reduce pathogen contamination of cattle carcasses during processing. Cattle hides are major sources of beef carcass contamination that occurs during processing (3, 5, 16). During the hide removal process, pathogens such as Escherichia coli O157:H7 and Salmonella are transferred from the hide, which carries high concentrations, to the carcass (1, 3, 5, 16). The current hazard analysis and critical control point plans (25) implemented in most beef processing plants in the United States focus on decontamination of the carcass by a combination of intervention strategies, including steam vacuuming, acid rinses, steam, and hot water spray (11). Such antimicrobial interventions combined with strict hygiene practices have significantly improved the microbial quality of beef carcasses in processing plants (1–3, 10). However, occasional process failures result in higher levels of contamination that cannot be effectively removed with current carcass interventions. Processes that effectively clean the hides before hide removal are successful in lowering carcass microbial contamination (5, 16). In an evaluation of chemical dehairing, * Author for correspondence. Tel: 402-762-4225; Fax: 402-762-4149; E-mail: [email protected]. † Names are necessary to report factually on available data; however, the U.S. Department of Agriculture neither guarantees nor warrants the standard of the product, and the use of the name by the U.S. Department of Agriculture implies no approval of the product to the exclusion of others that may also be suitable. Nou et al. first showed that the prevalence of E. coli O157: H7 on the carcass was almost eliminated when bacterial contamination of the hide was greatly reduced before hide removal (16). In subsequent studies with cetylpyridinium chloride (CPC), water washing followed by antimicrobial washes prior to slaughter also was highly effective in reducing carcass contamination during hide removal (5). CPC, however, is not yet approved for use inside beef processing plants. Other chemicals and antimicrobial compounds such as sodium hydroxide, trisodium phosphate, acidified chlorine, and phosphoric acid are approved for use in processing plants and are effective for carcass and boneless beef trim decontamination (2, 9, 12, 18–20). The use of these compounds on hides has not been evaluated. Therefore, the first objective of the present study was to evaluate the use of these antimicrobials as wash steps to reduce hide contamination in vitro. Because these materials do not have a neutral pH, a rinse also was needed to remove the residual antimicrobial to minimize exposure risks for plant personnel. Rinse compounds evaluated were water and acidified chlorine, which also has antimicrobial effects. Wash and rinse steps left excess liquids on the hides that could easily run onto the carcass when the hide was opened. To prevent excess liquid on the hide from contaminating the carcass, a vacuuming step to remove liquids also was J. Food Prot., Vol. 68, No. 2 266 BOSILEVAC ET AL. TABLE 1. Effect of various wash and rinse combinations and vacuuming on coliform counts of hidesa Washb Rinsec n Coliform countd Control Treated Treated 1 vacuumede Water Chloroform Phosphoric acid Sodium hydroxide Trisodium phosphate Water Water Water Water Water 30 30 30 30 30 5.9 6.2 5.8 5.7 5.9 4.3 2.6 3.3 4.2 4.4 2.3 2.6 2.3 1.8 3.4 Water Chloroform Phosphoric acid Sodium hydroxide AC-200 AC-200 AC-200 AC-200 30 24 24 24 5.7 5.9 5.9 6.0 2.8 3.2 2.3 3.2 2.8 2.0 1.6 2.2 Chloroform Phosphoric acid Sodium hydroxide AC-500 AC-500 AC-500 21 21 21 5.9 5.6 5.9 2.0 1.5 2.2 1.5 0.2 2.0 a Values represent the mean log CFU/100 cm2. Standard error of the mean ranged from 0.16 to 0.20. The minimum significant difference (P , 0.05) between any two values was 0.5 log CFU/100 cm2 (i.e., when the difference between any two values is $0.5, the difference is significant). b Wash steps consisted of 20-s end-to-end passes using high pressure (1,200 lb in22) application of water, 4% chloroform, 4% phosphoric acid, 1.6% sodium hydroxide, or 4% trisodium phosphate. c Rinse steps consisted of water or acidified chlorine at 200 ppm (AC-200) or 500 ppm (AC-500) applied at high pressure in 20-s endto-end passes. A 10-s dwell time occurred between wash and rinse applications. d Samples were serially diluted to a predetermined range in buffered peptone water and plated to Petrifilm E. coli or coliform count plates. e Alternating halves of each treated hide were vacuumed to remove excess liquid and visible contamination before the sample was collected. evaluated to determine whether it increased or decreased the effectiveness of the decontamination procedure. The second objective of this study was to evaluate the practical application, inside the processing plant, of a hide wash and rinse using a specially designed on-line hide decontamination wash cabinet. The efficacy of the hide-wash cabinet was determined by measuring the reduction in bacterial indicators and the prevalence of E. coli O157 on hides and preevisceration carcasses before any carcass interventions were applied. MATERIALS AND METHODS Experiment 1: comparison of wash and rinse chemicals for reducing hide contamination. At a beef processing plant, whole pulled hides were draped over barrels to simulate hide-on carcasses for evaluation of hide decontamination treatments. Sample sponges do not pick up the same level of bacteria from dry hides as they do from wet hides (21). Therefore, a low-pressure hand pump sprayer was used to briefly (3 s) spray water on control sample sites to prevent controls from underrepresenting counts. After control samples were obtained, the appropriate wash and rinse combinations were applied to the hides. Twelve treatment combinations were evaluated with and without an additional vacuuming step in an incomplete block design. Wash steps used one of the following: water, 1.6% sodium hydroxide (Birco Corporation, Henderson, Colo.), 4% chlorofoam (Tergo Industries Limited, New Lynn, Auckland, New Zealand), 4% trisodium phosphate (Simple Green, Huntington Harbour, Calif.), or 4% phosphoric acid (Birco). Rinse steps used either water or acidified chlorine at concentrations of 200 or 500 ppm. The wash plus rinse combinations evaluated are shown in Table 1. Water used for washing and for diluting the antimicrobials was from a local potable water tap. The sodium hydroxide, trisodium phosphate, and phosphoric acid were diluted to working concentrations according to the directions from the manufacturers. Chlorofoam is a chlorinated alkaline detergent. According to the specification of the manufacturer, when prepared at 4%, chlorofoam has a pH of 12 and 1,200 ppm free chlorine. The acidified chlorine used in the rinse steps was prepared by diluting sodium hypochlorite (household bleach) and adjusting it to a pH of 7.0 with glacial acetic acid. The total chlorine content of the acidified chlorine was calculated to be 200 or 500 ppm. The free chlorine of the acidified chlorine solutions