Food Protection Trends - October 2008 - 720

TABLE 9. Combinations of temperature and time providing a minimum 2-log reduction in E. coli on knife blades after a pre-rinse at 40°C — adapted from Goulter et al. (14) Temperature (°C) 60 65 70 75 80 82 1 Time (s) 20 20 5 1 1 1 Log reduction E. coli (SD) 2.72 (0.48) 3.50 (1.11) 3.46 (0.47) 2.70 (0.39) 3.41 (1.20) 3.44 (0.34) Blades swabbed with Whirlpak sponges; E. coli enumerated on E. coli/Coliform Petrifilm at 37°C for 2 days On the sheep floor (Table 8), the mean log TVC/cm2 of knives was 1.95 after the current knife sanitizing process and 1.7 after the alternate procedure. This constituted a significant overall difference in average log TVC/cm 2 (P = 0.014). However, this reduction was not consistent for all work stations, with significantly larger falls being observed at the forequarter, pluck removal and pluck table stations compared with sticking, ventral cut or evisceration. No significantly higher average log TVC/cm2 values were observed with the alternative procedure at any of the 13 work stations. With use of the current system, E. coli was isolated from sanitized knives on 24/130 (18.5%) occasions, compared with 29/130 (22.3%) occasions with the alternative system. The mean log E coli count of positive knives was 0.90/ cm2 and 0.76/cm2 with use of the current and alternative systems, respectively. In the alternative system used in the investigation reported above, rinsing knives in hand wash water was followed by a 2-knife sanitizing system with 60°C water so that knives had a longer residence time. Residence time varied according to work station, from more than 30 seconds at legging on the beef floor to 1–2 seconds at the heads off and ventral cut (teats removal) station on the mutton floor (data not included). In Australia, regulatory aspects of implementing an alternative knife sanitizing regime at temperatures below 82°C on the slaughter floor were considered by the Meat Standards Committee (MSC) of the Australia and New Zealand Food Regulation Ministerial Council. The MSC set conditions for approval of an alternative procedure that involved an establishment using a model that integrated temperature, time and reduction of E. coli to demonstrate a reduction of E. coli of at least 99% (2 log reduction) at each work station (19). For establishments wishing to export, a further condition was that the alternative should meet importing country requirements. The 2-log reduction was based on industry performance as reported for beef and sheep slaughter establishments (2, 3, 13). To provide scientific underpinning for temperature and time regimes for cleaning knives, a study was undertaken of the response of E. coli on meat-soiled knives to time-temperature combinations ranging from 1 to 60 s and 60° to 82oC (14). Combinations providing a minimum 2-log inactivation of E. coli are presented in Table 9. The work of Goulter et al. (14) can be used by companies intending to install an alternative procedure based on a twoknife system. From a regulatory viewpoint, it will be necessary to demonstrate that, at each work station, the knife is resident in water of a specified temperature for at least the time specified by the model. For example, a company wishing to use 60°C water would need to have the knife that is not in use immersed for a minimum of 20 s, which will not be sufficient for all work stations on a sheep chain processing 10 animals per minute. However, 70°C immersion would probably satisfy requirements at all work stations on beef and sheep slaughter floors in Australia, where average line speeds are around 75 and 480 head per hour, respectively. Midgley and Eustace (13) document other potential benefits of using temperatures below 82°C for cleaning knives, including: • Reduced risk of operator injury through scalding; • Reduced hot water consumption during knife and equipment cleaning; • Reduced impact of hot water on effluent treatment; • Reduced fogging and condensation; • Potential reduction in maintenance requirements. CONCLUSIONS Earlier in this review we commented that ‘sterilize’ is an inappropriate term when used in relation to treating knives during production. We also commented that because no process criteria have been set for the performance of the tool “sterilizers” in meat production plants, it is moot whether “sanitize” or “disinfect” are appropriate terms, since both imply elimination or reduction to an acceptable level of microorganisms of public health importance. The 2005 EU guidance document (11) makes the important statement, “The requirement [for disinfecting tools] is to ensure that meat is not contaminated through knives and equipment”. Recent available evidence suggests that the numbers of bacteria on knives in abattoirs are reduced by 1 to 2.5 log units by the current rinsing and sanitizing 720 FOOD PROTECTION TRENDS | OCTOBER 2008

Food Protection Trends - October 2008

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