Iowa State University Food SafetyHot Water Rinses as a Bacteriological Intervention Strategy onSwine CarcassesJ S. Dickson, professorDepartment of MicrobiologyASL-R1606Summary and ImplicationsHot water rinses were applied to the forelegs ofhog carcasses intentionally contaminated with manure.The water temperature varied from ambient temperature(25oC) to 82oC. The hot water washes were followed by a1.5% acetic acid rinse, and the carcasses were sampledbefore the hot water rinse, after the rinse and after the acidrinse. The hot water rinses reduced the total aerobicpopulation by approximately 2 log10 cycles and thepopulation of Enterobacteriaceae by approximately 2.5log10 cycles. The acid rinses reduced the total aerobicpopulation by an additional 0.3 log10 cycle (total of 2.3log10 cycles) and the population of Enterobacteriaceae tobelow detectable limits (total of 4 log10 cycles). Theexperiments were repeated in a commercial slaughteroperation, with similar results.IntroductionMicrobial contamination of animal carcasses duringslaughtering is an unavoidable problem in the conversionof live animals to meat for consumption. Much of theinitial contamination comes from the hide duringremoval. The exposed surface of the hide and the hairaccumulates dust, dirt, and fecal material (3). It has beendemonstrated that slaughter instruments could spreadcontamination into the internal organs of beef cattle, forinstance. The workers in slaughter operations also can bea source of contamination, as Salmonella spp. andEscherichia coli has been isolated from the hands ofworkers even after thorough washing. A variety ofmethods have been developed to reduce the levels ofcontaminating bacteria on carcasses, although most of thecurrent methods focus on washing and sanitizingprocedures (4).Decontamination of carcasses with hot water couldhave several advantages over the use of chemicals.Paterson (1969) reported that beef carcasses treated with asteam and hot water spray (80oC-96oC) for 2 mincontained significantly lower bacterial number. Eventhough some discoloration on the carcass surface occurredinitially, the normal color returned after cooling for 24hours (1). Hot water treatments also have resulted insignificant reductions in bacterial populations on hogcarcasses (5). Animal carcasses are known to becontaminated with a variety of pathogenic bacteria,including Salmonella, Campylobacter, E. coli andListeria. High-pressure washing with only water hasfound to reduce the total aerobic and Enterobacteriaceaecounts by 1 and 1.5 log cycles, respectively (2).Immersion in water at 80oC for 10 seconds of whole sheepcarcasses taken off the end of the slaughter line in acommercial abattoir destroyed 99% of the contaminatingcoliform organisms and 96% of the total number ofaerobic bacteria initially present on the surface tissues (6).Because much of the laboratory data was reportedpreviously, this report focuses on the research conductedin the slaughter establishment.Materials and MethodsMarket weight hogs were intentionally contaminatedwith fresh manure on their jowls. One jowl on eachcarcass was skinned, whereas the other was scalded. Thejowls were washed with 82oC water, which reached thecarcass at approximately 65oC. The water was appliedwith a low-pressure applicator operating at 25 psi.Following the water rinse, the carcasses were sanitizedwith acetic acid (1.8 % vol: vol) by using a commercialacid rinse cabinet.Microbiological samples were taken by swabbing anarea of the inoculum equivalent to 20 cm2. The sampleswere sent to a commercial testing laboratory, where theywere analyzed quantitatively for total mesophilic aerobicbacteria, total coliforms, generic E. coli and qualitativelyfor Salmonlellae.Iowa State University Food SafetyResults and DiscussionFigure 1 shows the effects of hot water and acid rinseson the populations of aerobic mesophilic bacteria, totalcoliforms, and generic E. coli on scalded hog carcasses.The combination treatment of hot water and organic acidreduced the aerobic mesophilic populations byapproximately 2 log10 cycles, and the total coliformpopulations by approximately 2.4 log10 cycles. Thepopulation of generic E. coli was reduced from log10 2.4to levels that were at the limit of detection for themethods used.Figure 2 shows the effects of hot water and acetic acidrinses on skinned hog carcasses. The patterns of reductionwere similar to those seen with scalded hogs, althoughthe final populations of total coliforms and generic E. coliwere slightly higher.References1. Barkate, M L., G R. Acuff, L M. Lucia and D S.Hale. 1993. Hot water decontamination of beefcarcasses for reduction of initial bacterial numbers.Meat Sci. 35:397-401.2. Dickson, J.S. 1988. Reduction of bacteria attachedto meat surfaces by washing with selectedcompounds. J. Food Prot. 51:869-873.3. Dickson, J S., and M E. Anderson. 1991 Control ofSalmonella on beef tissue surfaces in a model systemby 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. 1992Microbiological decontamination of food animalcarcasses by washing and sanitizing systems: areview. J. Food Prot. 55: 133-140.5. Eggenberger-Solorzano, L, and J S. Dickson. 1996.Hot water rinses as a bacteriological interventionstrategy on swine. Proceedings of the Tri-State FoodSafety Consortium Annual Meeting, Kansas City,MO. 20-22 Oct.6. Smith, M G., and A. Graham. 1978. Destruction ofEscherichia coli and Salmonellae on muttoncarcasses by treatment with hot water. Meat