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Hot Water Rinses as a Bacteriological Intervention Strategy on Swine Carcasses



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Iowa State University Food Safety Hot Water Rinses as a Bacteriological Intervention Strategy on Swine Carcasses J S Dickson professor Department of Microbiology ASL R1606 Summary and Implications Hot water rinses were applied to the forelegs of hog carcasses intentionally contaminated with manure The water temperature varied from ambient temperature 25oC to 82oC The hot water washes were followed by a 1 5 acetic acid rinse and the carcasses were sampled before the hot water rinse after the rinse and after the acid rinse The hot water rinses reduced the total aerobic population by approximately 2 log10 cycles and the population of Enterobacteriaceae by approximately 2 5 log10 cycles The acid rinses reduced the total aerobic population by an additional 0 3 log10 cycle total of 2 3 log10 cycles and the population of Enterobacteriaceae to below detectable limits total of 4 log10 cycles The experiments were repeated in a commercial slaughter operation with similar results Introduction Microbial contamination of animal carcasses during slaughtering is an unavoidable problem in the conversion of live animals to meat for consumption Much of the initial contamination comes from the hide during removal The exposed surface of the hide and the hair accumulates dust dirt and fecal material 3 It has been demonstrated that slaughter instruments could spread contamination into the internal organs of beef cattle for instance The workers in slaughter operations also can be a source of contamination as Salmonella spp and Escherichia coli has been isolated from the hands of workers even after thorough washing A variety of methods have been developed to reduce the levels of contaminating bacteria on carcasses although most of the current methods focus on washing and sanitizing procedures 4 Decontamination of carcasses with hot water could have several advantages over the use of chemicals Paterson 1969 reported that beef carcasses treated with a steam and hot water spray 80oC 96oC for 2 min contained significantly lower bacterial number Even though some discoloration on the carcass surface occurred initially the normal color returned after cooling for 24 hours 1 Hot water treatments also have resulted in significant reductions in bacterial populations on hog carcasses 5 Animal carcasses are known to be contaminated with a variety of pathogenic bacteria including Salmonella Campylobacter E coli and Listeria High pressure washing with only water has found to reduce the total aerobic and Enterobacteriaceae counts by 1 and 1 5 log cycles respectively 2 Immersion in water at 80oC for 10 seconds of whole sheep carcasses taken off the end of the slaughter line in a commercial abattoir destroyed 99 of the contaminating coliform organisms and 96 of the total number of aerobic bacteria initially present on the surface tissues 6 Because much of the laboratory data was reported previously this report focuses on the research conducted in the slaughter establishment Materials and Methods Market weight hogs were intentionally contaminated with fresh manure on their jowls One jowl on each carcass was skinned whereas the other was scalded The jowls were washed with 82oC water which reached the carcass at approximately 65oC The water was applied with a low pressure applicator operating at 25 psi Following the water rinse the carcasses were sanitized with acetic acid 1 8 vol vol by using a commercial acid rinse cabinet Microbiological samples were taken by swabbing an area of the inoculum equivalent to 20 cm2 The samples were sent to a commercial testing laboratory where they were analyzed quantitatively for total mesophilic aerobic bacteria total coliforms generic E coli and qualitatively for Salmonlellae Iowa State University Results and Discussion Figure 1 shows the effects of hot water and acid rinses on the populations of aerobic mesophilic bacteria total coliforms and generic E coli on scalded hog carcasses The combination treatment of hot water and organic acid reduced the aerobic mesophilic populations by approximately 2 log10 cycles and the total coliform populations by approximately 2 4 log10 cycles The population of generic E coli was reduced from log10 2 4 to levels that were at the limit of detection for the methods used Figure 2 shows the effects of hot water and acetic acid rinses on skinned hog carcasses The patterns of reduction were similar to those seen with scalded hogs although the final populations of total coliforms and generic E coli were slightly higher Food Safety References Barkate M L G R Acuff L M Lucia and D S Hale 1993 Hot water decontamination of beef carcasses for reduction of initial bacterial numbers Meat Sci 35 397 401 2 Dickson J S 1988 Reduction of bacteria attached to meat surfaces by washing with selected compounds J Food Prot 51 869 873 3 Dickson J S and M E Anderson 1991 Control of Salmonella on beef tissue surfaces in a model system by pre and post evisceration washing and sanitizing with and without spray chilling J Food Prot 54 514 518 4 Dickson J S and M E Anderson 1992 Microbiological decontamination of food animal carcasses by washing and sanitizing systems a review J Food Prot 55 133 140 5 Eggenberger Solorzano L and J S Dickson 1996 Hot water rinses as a bacteriological intervention strategy on swine Proceedings of the Tri State Food Safety Consortium Annual Meeting Kansas City MO 20 22 Oct 6 Smith M G and A Graham 1978 Destruction of Escherichia coli and Salmonellae on mutton carcasses by treatment with hot water Meat Sci 2 119 128 1


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