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mocouples at their geometric center and heated in the controlled vapor oven set at 130°F (54.4°C) Twb. When the roasts reached a temperature of 130°F (54.4°C), they were removed from the oven and placed in a refrigeration unit set at 38°F (3.3°C) and with a restricted airflow to allow slow cooling. One roast was uncovered, and one was covered with aluminum foil. This trial indicated that the roasts without a foil cover cooled from 130 to 41°F (54.4 to 5°C) in about 24 hours, thus assuring the germination and multiplication of surviving C. perfringens.

ings. The processing and sampling steps for the beef roasts were as follows: 1. At time-zero, 1 roast was surface inoculated with only Salmonella; 3 roasts were surface inoculated with Salmonella and contained 3 inserted dialysis sample units of both Salmonella and C. perfringens; 3 roasts contained only inserted dialysis sample units of C. perfringens. The first inoculated roast, the control, was immediately surface sampled for Salmonella and center sampled for C. perfringens. 2. The controlled vapor oven was set at 130°F (54.4°C) Twb and 170°F (76.7°C) Tdb and preheated. 3. Three roasts were placed on a 18 × 26 inch sheet pan on the bottom rack of the controlled vapor oven, and 3 roasts were placed on a pan on the middle rack in the oven. 4. The roasts were set to cook for 6 hours to achieve a center temperature of 130°F (54.4°C). At the end of the 6 hours, 1 roast was removed from the oven. The 3 internal Salmonella samples in dialysis tubes were recovered and removed, along with the 3 C. perfringens samples in dialysis tubes. The presence of Salmonella on the roast surface was determined by excising the 10 cm2 surface sample for Salmonella recovery and enumeration. 5. After the 6-hour cook, the Twb of the oven was left at 130°F (54.4°C), and the Tdb was set at 131°F (55°C). These settings were used to hold the beef at a center temperature of 130°F (54.4°C) and a surface temperature of 131°F (55°C) at 90% relative humidity for 121 minutes, to meet the FDA Salmonella reduction requirement (8). At the completion of this 121-minute holding step #1 (i.e., 8 hours and 1 minute after start of cook), one inoculated roast was removed from the oven for dialysis sample tube recovery and determination of Salmonella and C. perfringens.

Processing and physical data recording
Each of the 6 roasts that contained the dialysis sample units was fitted with 2 thermocouples (one internal thermocouple at the geometric center adjacent to the inserted dialysis units and a second thermocouple at 1.6 mm below the surface), for a total of 12 thermocouples. Internal and near-surface temperatures of the designated roasts were recorded at 5-min. intervals throughout the cooking, holding, cooling, and reheating procedures. Oven temperature was also monitored. The Tdb temperature and relative humidity in the controlled vapor oven were electronically recorded (5- or 10-min. intervals) during all processing steps, using type K thermocouples, an Omega OMB-DAQ-55 USB data acquisition system with a OMB-PDQ1 expansion module (Omega Engineering, Stamford, CT) and a humidity probe (Global Sensors’ Humidity Logger DWHS-B-16, Mt. Holly, NC – Accuracy of 3% to 60°C and 5% to 77°C). The temperature in the refrigerator was also electronically monitored and recorded during the cooling cycle and subsequent refrigerated holding. The temperature and relative humidity display readings on the controlled vapor oven were manually recorded from the oven display panel at approximately 1-hour intervals and whenever samples were collected during processing (i.e., initial cook-hold and retherm (reheating)). Additionally, 1 roast was fitted with an internal temperature probe that was integral with the controlled vapor oven for manual record-

6. Holding continued at 130°F (54.4°C) Twb and 131°F (55°C) Tdb for 28 hours to simulate restaurant hot holding. At the completion of this step, about 36 hours after start of cooking, one inoculated roast was removed, and Salmonella was recovered and enumerated from the surface of the roast. Salmonella and C. perfringens were recovered and enumerated from the dialysis tube samples within the center of the roast. 7. The remaining 3 roasts (which contained only C. perfringens dialysis tube samples) were placed in a refrigerator and cooled from 130°F (54.4°C) center temperature to 41°F (5°C) in about 24 h. After cooling to 41°F (5°C) center temperature, 1 roast was removed, and the 3 C. perfringens dialysis tubes from the center of the roast were removed for C. perfringens recovery and enumeration. 8. The remaining 2 roasts were held refrigerated at 38 to 41°F (3.3 to 5°C) for about 24 h. After this refrigerated hold, 1 roast was removed, and the 3 dialysis tubes were extracted for C. perfringens recovery and enumeration. 9. For the final step, the remaining refrigerated roast was reheated for 6 hours in the controlled vapor oven set at 130°F (54.4°C) Twb and at 170°F (76.7°C) Tdb. At 6 hours, the Tdb was changed to 131°F (55°C) and the roast was held for an additional 4 hours. The roast was then removed from the oven, the dialysis tube samples were removed from the roast, and C. perfringens was recovered and enumerated.

Recovery
For recovery of inoculated samples, the 10-g contents of a dialysis tube were placed in a Stomacher bag with BPB to obtain a 1:10 dilution. Samples were stomached for 1 minute and the homogenate serially diluted in BPB. For the surface Salmonella inoculated samples, the designated inoculation sites (10

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Food Protection Trends - April 2010

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