Food Protection Trends - October 2008 - (Page 716)

TABLE 3. Total viable counts (TVC) of knives1 and hands before rinsing and after rinsing (hands) and after rinsing and immersion in 82°C water (knives) on a beef slaughter floor — adapted from Bell 1997 (2) Station Mean log TVC/cm2 (SD) Before cleaning After cleaning 3.61 (0.47) 4.74 (0.67) 2.64 (0.44) 3.73 (0.42) Knife blades (n = 20) Knife hands (n = 20) 1 Blades swabbed with cotton gauze swabs; counts at 25°C for 72 h licensed to export to the EU. The world’s largest exporter of beef, Brazil, has over 60 abattoirs licensed for export to the EU. Of interest is the fact that in these two countries, none of these 120 abattoirs reportedly employs a two-knife system. Effectiveness of current practices There are no guidelines and no published information on how to assess whether knives actually are significant sources of contamination of carcasses or how to determine the extent of regular disinfection that is necessary. However, there are studies that can be used as a guide. The effect of washing the knife followed by a momentary dip in 82°C water during sheep and beef processing was investigated in New Zealand abattoirs (Tables 2 and 3). Bell and Hathaway (3) measured the effect of knife cleaning at the work station where opening cuts on the hind legs of lamb carcass are made. Before cleaning, knives had a mean log TVC/cm2 of 5.04, reflecting the heavy soiling that can occur from the fleece. Rinsing the knife in hand wash water at 44°C removed 98.2% of contamination (1.8 log reduction) from the blade and, after subsequent dipping in 82°C water, 99.8% of contamination was removed, to effect a 2.6 log reduction (Table 2). Bell (2) found that on the beef floor, contamination on knife blades approximated that of the hide on the hind legs (mean log TVC/cm2 of 3.61). Cleaning the knife by rinsing it in hand wash water and then dipping it in 82°C water reduced the loading on the blade to mean log 2.64/cm2, a 1 log reduction. The studies of Bell and Hathaway (3) and Bell (2) are also of interest because they indicate that the knife hand was generally one log scale more contaminated than the knife blade after washing of hand and knife. In Australia, Eustace et al. (13) and Reyes-Veliz (pers. comm.) studied the microbiological status of knives pre-rinsed under a warm water spray, before a momentary dip in 82°C water. Knives were tested at a range of stations located along beef, mutton and pig slaughter floors, and E. coli prevalences and total viable counts (TVCs) were obtained. In Table 4 are presented TVCs and E. coli prevalence on cleaned knives used at stations along the beef chain. The overall mean log TVC/ cm2 was 2.18, and E. coli was isolated from cleaned knives on 20/230 (8.7%) occasions, with a mean E. coli count on positive knives of log 0.43/cm2. In general, higher TVCs occurred earlier in the process, when cuts were made through the hide, and particularly when air knives were used or when knives were used at the head stations. In Table 5 are presented TVCs and E. coli prevalence on knives used at stations along the mutton chain. The mean log TVC/cm2 was 1.95, and E. coli was isolated from cleaned knives on 24/130 (18.5%) occasions, with a mean log E. coli on positive knives of 0.90/cm2. Higher TVCs were associated with knives used to incise the brisket, to trim exposed neck tissue, to ring the bung (incise the anus), and to remove the viscera. Total viable counts on knives after cleaning on a pig slaughter floor (Table 6) indicated a mean log of 1.98/cm2. E. coli were found on 7/30 (23.3%) of cleaned knives, and the mean log of positive knives was 0.25/cm2. The results of Bell and Hathaway (3) indicate that most of the reduction in bacteria on the knife blade is attributable to the spray rinse. Similarly, it was found (20) that rinsing the knives under streams of washwater (20–40°C) before immersing them in a sterilizer removed at least 70% of bacteria. From the foregoing, it is clear that the most common knife decontamination process (rinsing in warm water followed by a momentary dip in 82°C water) does not always result in removal of fecal organisms, as evidenced by the E. coli counts on 8.7%, 18.5% and 23.3% of cleaned knives used for beef, sheep and pig dressing, respectively. However, the knives themselves, even after rinses in tepid water, are clearly not major sources of contamination either. The TVCs reported after a spray rinse (log 3.3 / cm 2) and after rinsing in tepid hand wash water (log 1.6/cm2) attest to this (3, 13). Recent national surveys of the microbiological quality of beef and sheep carcasses in Australia (23, 24) indicate low aerobic plate counts and low prevalence of E. coli. There is no reason to conclude that the current procedures for rinsing and dipping knives are contributing in any significant way to contamination of meat. ALTERNATIVE PROCEDURES FOR KNIFE CLEANING Ultrasound and other physical alternatives There is little published research on the efficacy of ultrasound for cleaning knives. Ultrasonic cleaning of knives in water baths was examined at different temperatures (26). It was found that the protein deposition on the knife was much reduced by ultrasound at 82°C. The authors recommended using ultrasonic cleaning at room temperature before disinfection. Midgley and Eustace (20) investigated the use of a prototype commercial ultrasound bath designed for knife cleaning. Reductions in microbial load on knives coated in fat or minced meat were slightly increased when ultrasound was used in conjunction with hot water treatments. Chemical alternatives The European Commission’s Scientific Committee on Veterinary Measures 716 FOOD PROTECTION TRENDS | OCTOBER 2008

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Food Protection Trends - October 2008 Contents Sustaining Members Perspectives from Your President Commentary from the Executive Director Employee Motivators for Following Food Safety Practices: Pivotal Role of Supervision Knife Sanitizing in Abattoirs: The Effectiveness of Current and Alternative Practices Call for Nominations – 2009 Secretary Call for Awards – IAFP 2009 New Members Updates Industry Products Coming Events Advertising Index Journal of Food Protection Table of Contents Audiovisual Library Order Form Booklet Order Form Membership Application

Food Protection Trends - October 2008

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