107 Journal of Food Protection, Vol. 48, No. 2, Pages 107-111 (February 1985) Copyright" International Association of Milk, Food, and Environmental Sanitarians Beef Jerky: Fate of Staphylococcus aureus in Marinated and Corned Beef during Jerky Manufacture and 2.5 C Storage RICHARD A. HOLLEY Food Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario KIA 0C6, Canada Downloaded from http://meridian.allenpress.com/jfp/article-pdf/48/2/107/1656582/0362-028x-48_2_107.pdf by guest on 23 September 2021 (Received for publication April 25, 1984) ABSTRACT MATERIALS AND METHODS A domestic food dehydrator was used to prepare beef jerky Jerky preparation from inside round steak and corned beef brisket slices contami­ Beef jerky was made from fresh or cured beef purchased at retail outlets. In these experiments, inside round steak and vacuum packed nated with Staphylococcus aureus. The number of added corned beef brisket weighing about 500 g each were used. Meats were staphylococci doubled within 2 h after the start of drying corned defatted and placed at -20°C for 10 min before slicing. Samples were beef slices. About 3-3.5 h were required for corned beef and cut into 6.4-mm (0.25 inch) thick slices across the muscle fibers with between 1-2.5 h for inside round slices to reach an aw of 0.86. a meat slicer (Globe Slicing Machine Co. Inc., Stamford, CT). Slices Only 15% of all staphylococci initially present survived 8 h of inside round steak were held 12 h at 4°C in a "Great Jerky" of heated-drying, and this was reduced to 5% after a week of marinade which contained salt, garlic pepper, brown sugar, garlic salt, refrigerated storage of slices. The safety of beef jerky produced soy and Worchestershire sauces (3). Slices of corned beef brisket were in the home is assured when wholesome meats used in its prep­ held at 4°C for 12 h before drying but were not marinated. Strips of aration are rapidly dried. lean meat were placed in the circular (0.38-m diameter) trays of a Har­ vest Maid Dehydrator, (model FD-101, Alternative Pioneering Systems, Inc. Minneapolis, MN), in a single layer and dried. Temperature was set at 155°F for 4 h and reduced to 140°F for an additional 4-h period. The internal temperature of the dehydrator was monitored using a Fluke Jerky can be made from either sliced raw meat or fish model 2100A digital thermometer, (J. Fluke Mfg. Co. Inc., Seattle, which has been salted, spiced and may be smoked before Wash.), equipped with a copper-constantan type T precalibrated ther­ being dried (3). Beef jerky is classifiable as a fully dry mocouple. The temperature probe was placed at 12 sites on the drying trays at each machine operating temperature. shelf-stable product (7, 8). Historically, in North America beef jerky was a very Bacterial analyses important food commodity which substituted for fresh Meat samples (11.0 g) were taken at 2-h intervals, chopped to form beef in areas where dependable refrigeration was not 6-mm cubes, added to 99 ml of phosphate-sulfate buffer (6) and treated 15 s with a Polytron tissue homogenizer, (model PT-35, Kinematica available. Today, jerky is a popular snack meat among GmbH, Lucerne, Switzerland) and analyzed for viable bacteria as indi­ campers and hikers where food stability, protein content, cated below. light weight and expense are keys to dietary choice. Staphylococcus aureus ATCC 27661 was used to contaminate meat Snack sausages are also very popular among this group slices from inside round steak and corned beef brisket. After overnight but are higher in fat. storage of 500 g of marinated steak and 500 g of corned beef slices, meat was dipped into a 24-h-old nutrient broth culture of S. aureus Smith et al. (13) inoculated a non-fermented all beef containing 2.6 x 108 cells/ml. Slices were briefly blotted with paper snack sausage with Salmonella and Staphylococcus, towels, drained in a beaker and placed in 4 trays of the food dehyd­ C which was heated for 3.5 h at 51.1-52.2 C and dried for rator. The latter was operated in a laminar flow biohazard hood, (model 4 d at 21°C and 50-55% RH. At the end of this process, B6-MM-99-T2, Canadian Cabinets Co. Ltd., Montreal, P.Q.). The fol­ the product was not pathogen-free. No viable food- lowing day 500 g of uncontaminated meat was similarly dried. poisoning organisms were found in other sausages that Total bacteria were enumerated using plate count agar (PCA) incu­ bated at 32°C for 48 h; lactobacilli by incubation of MRS agar, 32°C, had been heated at an internal temperature of 53.9-55cC 48 h, anaerobic; coliforms by overlaid violet red bile agar, VRB, 32°C, or 57.8-58.9°C for 3.5 h and dried as above. 48 h; and staphylococci (pre-poured Baird-Parker agar, BP, 37°C, 48 Little technical information was available to assist in ti). One-ml samples were split into three approximately equal portions a safety evaluation of a commercial recommendation (3) and surface-spread on BP agar. Micrococci were counted on BP plates for the use of 4-h drying at 68°C (155°F) plus 4 h at as tellurite-reducing colonies with a typical coagulase-negative reaction. A portion of homogenized sample was heated for 15 min at 80°C and 60°C (140°F) for jerky preparation in the home. This analyzed for the presence of aerobic and anaerobic spores at 32°C study was undertaken to assess the safety of jerky prepa­ (PCA, 48 h). Plates for anaerobic incubation were placed inside either ration plus to examine the effect of brief refrigerated stor­ BBL or Oxoid anaerobic jars and BBL Gaspak C02-H2 generators were age upon surviving bacterial populations. used to create anaerobic conditions. All laboratory media for bacterial JOURNAL OF FOOD PROTECTION, VOL. 48, FEBRUARY 1985 108 HOLLEY growth were obtained from Difco Laboratories, Detroit. Procedures used from 105/g to 103/g in control samples and these or­ for enumeration of bacteria were described by Speck (14) and all sam­ ganisms increased initially in numbers but declined after ples were analyzed in duplicate. 2 h (Figs. 1A and IB). Storage On staphylococci-inoculated inside round, (Fig. 2A), To check survival of microorganisms in dried beef, freshly made the reduction in total aerobic bacteria reached 80%. The samples of jerky with or without added staphylococci, were packed in aerobic bacterial population on inoculated corned beef sterile Whirl-Pak bags (B1020, Nasco, Guelph, Ont.) and placed in a brisket slices seemed to survive better, with about only domestic refrigerator at 2.5°C. Total numbers of bacteria, staphylococci, a 7% loss in viability during 8 h of drying (Fig. 2B). micrococci and water activity (aw) were monitored at 8 and 9 d follow­ ing manufacture. This improved viability did not appear to be due to the presence of the added staphylococci since, in both the Water activity inside round and corned beef, 85% of the staphylococci Samples for aw measurement were taken in duplicate, chopped to initially present were killed during the 8-h drying period form 6-mm cubes, placed in covered sample dishes and equilibrated (Figs. 2A and 2B). to 25±0.1°C. Measurement of aw was made with a Beckman VFB hyg- roline recorder (Beckman Instruments Inc., Cedar Grove, NJ) at 25°C. Downloaded from http://meridian.allenpress.com/jfp/article-pdf/48/2/107/1656582/0362-028x-48_2_107.pdf by guest on 23 September 2021 Saturated aqueous slurries of K2Cr207, KC1, and NaCl were used as standards to represent water activities of 0.980, 0.843 and 0.753, re­ spectively (10). RESULTS Drying temperatures Commercial literature (3) advised that meat strips be dried at 155°F (68.3°C) for 4 h followed by 140°F (60°C) for another 4-h period. When measured, however, tem­ peratures inside the dehydrator at 12 loci were only 52.9±0.8°C (mean ±SD) when set at 68.3°C and were 48.2±0.4°C when set at 60°C. Although actual tempera­ tures were 15.4°C and 11.8°C lower than the desired high and low temperatures, the deviation from the mean tem­ perature was small among all test locations on the four trays. It was decided during these experiments to incorpo­ rate the temperature discrepancy of the machine set- pointer to fully represent the hazard to a consumer pre­ paring beef jerky in his home who would not have access to accurate temperature measuring devices. Meat drying experiments reported here were conducted using a 4-h drying period at 52.9±0.8°C (127.2°F) followed by an additional 4 h at 48.2±0.4°C (118.8°F). Bacterial analyses An immediate decrease in coliform number was noted from the start of drying meat slices (Figs. 1 and 2). Sporeformers on both inside round and corned beef slices generally increased within the first 2 h of drying (Figs. 1 and 2) but those on uninoculated corned beef slices increased only after the initial 4-h drying period (Fig. IB). Total numbers of bacteria recoverable on PCA agar were reduced during drying of uninoculated beef slices longer than 4 h. Almost half the organisms present in­ itially on inside round slices and greater than 75% of the total organisms present on corned beef brisket were not recoverable following 8 h of drying (Fig.