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Since 1995, over 140 patients with variant Creutzfedt-Jakob disease (vCJD) have died as a probably result of having consumed processed meat products contaminated with bovine spongiform encephalopathy (BSE). Although almost all cases have occurred in Great Britain, France and Italy, future cases may occur in any country where BSE exists. In the United States, the danger might come from chronic wasting disease (CWD) crossing over from deer, elk, moose or antelope to cattle. Given the multiple forms of CWD prions and the possibility of mutations, there is a very real danger of cross-over contamination. In addition, in-vitro studies conducted by Dr. Byron Caughey (NIH Labls, Hamilton, Montana) have shown cross-conversion of prions from deer, cattle, and humans.
There are presently two methods for inactivating prions: exposure to strong alkali or hypochlorite solutions and retorting. Chemical treatment of meat is unacceptable, and retorting under conditions that inactivate prions leaves meat products with a mushy texture and scorched flavor. However, high pressure (above 690 MPa) with an initial temperature between 80°C and 90°C at several short pulse exposures (1 minute each) inactivate 103 to 106 LD50 infectious prions per gram. The estimated maximum concentration of infectivity that could occur in processed meat from BSE-infected cattle is less than 10 LD50 per gram, so the conditions used in this study would ensure a high degree of safety from accidentally transmitted prion disease. In addition, this process will render the meat product free from conventional pathogens. The cost of the process is about $0.03 to $0.045 per pound, which is comparable to freezing and canning.
The stated objectives for this work were: Determine the organolyptic changes in selected beef products due to high pressure processing to inactivate pathogenic prions.
High-pressure test experimental design. Each meat product was pre-cooked if not already purchased pre-cooked (hot dogs and deli, sliced roast beef). The rib eye steaks, chuck roasts and hamburgers/seasoned hamburgers were fried on a commercial grill for 5 minutes per side at 375F (190°C). The hot dogs in the first sensory test were purchased at Sam’s Club (Albert Lee™ beef franks). The sausages in the second sensory test were made at a local meat shop (Blue Max, Puyallup, WA). The sausages were seasoned with German sausage seasoning (Newlywed Foods) with the following formula: 80.8% lean, ground chuck roast (15% fat) using a _inch grind, 8% water, 5% Betty Crocker™ dry potato buds, 1% TIC gum blend #881M, 3% NFDM, 2% seasoning blend and 0.2% nitrite-salt blend. The sausage was processed to 160°F (71°C). The hamburger in the first sensory test was purchased as preformed patties (1/3 pound) from Sam’s Club (Northern Plains™ Beef Sirloin and Beef Patties) at 15% fat. The hamburger patties in the second test were made from lean hamburger (7% fat) with 1% TIC gum blend colloid BIND # I 96 and 1 pouch of Lipton’s Beefy Onion soup mix (31 grams) per 454 grams of ground beef.
Each meat sample (300 grams per pouch except the sliced roast beef and hamburgers were at 100 grams per pouch) was vacuum packed into a 12 cm by 15 cm plastic pouch (0.75 mm nylon+ 2.25 mm polyethylene), sealed then repacked into another 12 cm by 15 cm plastic pouch (0.75 mm nylon + 2.25 mm polyethylene) with vacuum and sealed with an impulse sealer. Samples were preheated using a microwave oven until they achieved 95°C (about 4 to 6 minutes). The pouches were placed in a hot water bath (95°C). The samples destined for pressurizing were transferred to the high-pressure vessel plastic insert, which was placed in the pressure vessel. A duplicate set of samples from the 95°C water bath was chilled and labeled as untreated, control samples. The water in the high pressure vessel was checked to make sure that is was at the target 95°C prior to inserting test product. The vessel was closed and the process was then executed (3 one minute 690 MPa pulses with a one second, ambient pressure between the pulses). The process pressure, temperature and time were monitored and recorded by a computer. After processing, the samples were removed from the high-pressure vessel and placed in an ice bath. Samples were kept chilled until sensory tested.
Sensory testing experimental design. All the meat products were preheated to 110°F (43°C) in an oven set at 250°F (121°C) for a period of 60 to 120 minutes depending on the meat product. The meat was placed on a broiler tray with pre-heated water below and covered with foil to prevent drying. Each meat product was cut into 30 gram portions and presented to tasters as a paired comparison. The tasters were in separate tasting booths and were given rating sheets to fill out for each product. The tasters were from the local Portland area with 50 to 55 participating at each tasting. One panel was conducted in the morning and another conducted in the afternoon at the “Western Family Foods” test facilities in Portland, Oregon.
Two sensory tests were conducted: in the first test, hot dogs and hamburgers lost to the non-pressure treated samples while the pressure treated sliced roast beef, chuck roast and rib eye steak beat or equaled the non-pressure treated samples; in the second test, using reformulated hamburger and hot dog (German sausage) mixes, the pressure treated hamburger won and the pressure treated sausage tied with the non-pressure treated sample. The final sensory results are summarized below: (details are provided in Appendix A):
High pressure was expected to tenderize meat and enhance the flavor. The chuck roast was preferred by a 4 to 1 margin with a very desirable, tender texture and “roasted flavor” most often cited as the reason for preference. The same was true for the rib eye steaks except the margin for preference for high pressure processed steaks was 2 to 1. These rib eye steaks were USDA choice and were already tender. They were pre-grilled prior to the pressure treatment and had excellent flavor and texture. High pressure enhanced both flavor and texture. The pressure treated, deli-style, pre-cooked, pre-sliced roast beef was preferred by a 3 to 2 margin over the untreated control. Again the preference was due to increased tenderness and enhanced roasted flavors.
In the first sensory test, pressure treated, pre-grilled hamburgers became drier, tougher and lost to the untreated hamburgers by a 2 to 1 margin. However, the hamburger was reformulated to retain a moist, tender texture after pressure treatment by adding a USDA approved gum blend (carrageenan gum blend) and salt with seasonings. The pressure treated, reformulated hamburger was very tender and moist.
Pressure treated hot dogs had mushy textured centers and tasted more salty compared to the untreated hot dogs and lost by a 10 to 1 margin. Hot dogs are least-cost formulated to have sufficient bind to hold 30% fat and produce a suitable texture, but not to survive the stress of a high pressure treatment. The finely ground meat emulsion is denatured by high pressure which gives the hot dog a very soft, mushy texture. The hot dogs (German sausage formula) were reformulated by first using a lean meat blend (15% fat), using a coarse grind (1/2 inch plate) and drying to a lower moisture content by holding in the smokehouse until the internal temperature hit of 160°F (71°C). In addition, 5% dry potato buds were added to soak up free moisture and simulate fat texture. The pressure treated, reformulated hot dogs (German sausage formula) equaled the non-pressure treated version.
High pressure can be used to treat meat products to inactivate infectious prions such as bovine spongiform encephalopathy (BSE) and chronic wasting disease (CWD) without adversely affecting sensory characteristics. The process is economical, and in most instances improves the meat flavor and texture.