Microbial evaluation of steam pasteurization and comparison of Microbial evaluation of steam pasteurization and comparison of excision versus sponge sampling recovery excision versus sponge sampling recovery

The use of steam pasteurization (SPS400TM; Frigoscandia, Bellevue, WA) as a viable commercial-scale intervention method to treat pre-rigor beef carcasses uniformly hasbeen evaluated for temperatures from 180E to 201 ÌŠF. Effectiveness at lower temperatures(minimum atmospheric temperature of 170 ÌŠF) has not been evaluated. Previous studies of steam pasteurization used excision sampling. However, the USDA-FSIS has suggested use of nondestructive sampling of chilled beef carcasses for generic Escherichia coli, so we compared excision and sponge sampling in a commercial slaughter facility. Twenty-eight beef carcasses were monitored to determine the effectiveness of steam pasteurization and to compare the two sampling methods. Total aerobic mesophilic bacteria, E. coli, and coliform counts were all reduced (P≤0.01) by steam pasteurization. Sponge sampling of carcasses for E. coli. provided lower recovery (P≤0.01) than excision sampling. None of 28 carcasses tested positive by sponge sampling; however, six of the same microbial carcasses were positive (0.39-23.6 CFU/cm2) by excision sampling immediately adjacent to the sponged area. The SPS 400TM steam pasteurization unit, operating at a minimum atmospheric temperature of 170 ÌŠF reduced (P≤0.01) all bacterial populations on prerigor beef carcasses. Excision data, compared to previous commercial evaluations of the SPS 400TM at a slightly higher operating atmospheric temperature, provided comparable total reductions, but a few more E. coli survived at 170 F.


Summary
The use of steam pasteurization (SPS 400™; Frigoscandia, Bellevue, WA) as a (Key Words: Steam Pasteurization, Microbial viable commercial-scale intervention method Evaluation, Carcasses.) to treat pre-rigor beef carcasses uniformly has been evaluated for temperatures from 180E to 201EF.Effectiveness at lower temperatures (minimum atmospheric temperature of Microbiological safety of the food supply 170EF) has not been evaluated.Previous has been under intense scrutiny.Foodborne studies of steam pasteurization used excision disease outbreaks and large food recalls are sampling.However, the USDA-FSIS has causing increased concerns by consumers and suggested use of nondestructive sampling of producers.New regulations have been implechilled beef carcasses for generic Escherichia mented by the USDA-FSIS to minimize coli, so we compared excision and sponge contamination and proliferation of pathogens sampling in a commercial slaughter facility.
in food.Twenty-eight beef carcasses were monitored to determine the effectiveness of steam pas-Steam pasteurization, an intervention teurization and to compare the two sampling method that has been tested and verified in methods.Total aerobic mesophilic bacteria, commercial slaughter facilities, has reduced E. coli, and coliform counts were all reduced both indigenous flora and pathogens on (P#0.01) by steam pasteurization.Sponge freshly slaughtered beef carcasses.sampling of carcasses for E. coli.provided lower recovery (P#0.01)than excision sam-Our study evaluated the effectiveness of pling.None of 28 carcasses tested positive a steam pasteurization system (SPS 400™) by sponge sampling; however, six of the same operating at 170EF, based on microbial enucarcasses were positive (0.39-23.6 CFU/cm ) meration at several steps.Microbial recover-

Introduction
Experimental Procedures the cooler.All carcasses were surface sam-Counts were lower (P#0.01)with sponge pled using a circular coring device to excise samples than excision samples for all bacteria.21.2 cm of tissue at three locations (rump, Detection limits were 0.39 CFU/ cm for the 2 flank, and brisket) to create a composite excision method and 0.04 CFU/cm for the sample of 63.6 cm .All chilled carcasses sponge method.This means that the sponge 2 (18-24 hour) were surface sampled using method should detect bacterial colony formboth the coring device (excision) and the ing units, including E. coli colonies, more USDA-FSIS sponge sampling method at often than the excision method.However, in adjacent locations on the same carcass.All this study no E. coli colonies were detected samples were shipped overnight to the Kan-with sponge sampling, whereas E. coli colosas State University Food Microbiology nies were detected on some of the same Laboratory (Manhattan, KS) in insulated carcasses using the excision sampling coolers with cold-packs.During shipment, method.temperatures were monitored by data loggers and remained below 45EF.
Escherichia coli counts were compared All samples were enumuated within 1 day lished in the Federal Register, July 25, 1996. of collection for total aerobic mesophilic Only three unacceptable results were identibacteria, Escherichia coli, and coliforms, fied and were from carcasses sampled before using appropriate Petrifilm™ plates.The steam pasteurization.Using the excision excision samples were diluted with 0.1% method, one chilled carcass had a marginal peptone diluent.Sponges were rehydrated level of E. coli.All chilled carcasses had according to USDA-FSIS methods using acceptable test results for E. coli with sponge Butterfield's phosphate buffered dilution sampling.In conclusion, steam pasteurizawater (FDA Bacteriological Analytical tion decreased (P#0.01)all bacterial counts.Method).All plates were incubated 48 hours All excision samples from chilled carcasses at 95EF.Data were converted to log col-indicate that the slaughter process was in 10 ony forming units (CFU) per cm and mean compliance with FSIS E. coli criteria.How-2 values determined at each sampling step.A ever, reduction in SPS 400™ operating value one-half the detection limit was re-temperatures should be avoided if possible, as ported for samples with no colonies on the a margin of safety.lowest dilution, in order to be able to perform statistical analysis.Statistical significance The sponge sampling method revealed (P#0.01) was determined using Proc GLM in lower (P#0.01)counts for all bacterial types, the Statistical Analysis System (SAS) for compared to excision sampling.each bacterial type.

Results and Discussion
Total aerobic mesophilic bacteria, E. coli, and coliform counts were lower (P#0.01)after than before steam pasteurization and remained lower after a 18-24 hour chill.Bacterial counts after 18-24 hours in the cooler and immediately after steam pasteurization were similar (P>0.01).