The Ohio State University Meat Laboratory supplied the stimulated meat. A low voltage (40 volts) was used to stimulate one half of the carcass and other half was non-electrically stimulated. The electrodes of the stimulator were placed in the carcass round and in the atlas on the neck. Stimulation was done 45 times, each by 2.5 s on and 1.5 s off. The primal cuts were vacuum packaged for 10 d. Then, the beef round primal cuts were trimmed of visible fat and connective tissue. All beef bottom rounds were cut into uniform cubes of roasts (8×8×8 cm dimensions). The muscles were roasted in a hot-air convection oven (Type EFIII, The GS Blodgett Co Inc., Burlington, Vermont) at 168° C until the internal temperature (IT) of the roasts reached 71°C. After roasting, the meat products were chilled in a cooler (Model 7030 S/N 75368, Forma Scientific, Division of Mallinckrodt, Inc., Ohio, USA) until the internal temperature of the products reached 4°C. These meat products were separately placed into unsealed plastic bags for refrigerated storage (4°C) until being tested. Samples were reheated in a microwave (Model M312, 2450 Hz, Hobart Corp., Troy, Ohio, USA) to an IT of 60°C before conducting all evaluations, except for the microbiological test that was performed on non-reheated tissue.

Moisture content, pH values and crude fat contents were evaluated for compositions of raw material (Ockerman, 1985). A modified extraction of the TBARS method was used to analyze lipid oxidation (Pensel, 1990). The results of electrical stimulation were evaluated by yields, Warner-Bratzler shear value (Ockerman, 1985), and sensory test (Figure 1).

A 5-gram sample was analyzed by the modified extraction method of TBARS. The 5-gram sample of meat tissue was placed in a polyethylene bag. Fifty ml of chilled (4°C) solution of 20% trichloroacetic acid in 1.6% phosphoric acid was added to the same bag and massaged for two minutes in a stomacher to mix the sample. Fifty ml of chilled distilled water (4°C) was then added into the bag and the stomacher was again used to blend the sample for 30 s. The slurry was filtered through Whatman No. 1 filter paper into a 100 ml cylinder. Five ml of the filtrate was pipetted into a test tube, and five ml of fresh chilled 0.02 M 2-thiobarbituric acid solution was added to this tube. All samples in test tubes were placed in the dark at room temperature (25°C) for 15 h in order to develop the color reaction. The intensity of color was measured in a spectrophotometer at 532 nm to calculate the TBARS value.

Two point two grams of 1,1,3,3-tetraethoxypropane (TEP, FW = 220) was diluted to 1000 ml with distilled water to prepare for a 10⁻² M stock solution. A 10⁻³ M stock solution of TEP was prepared by diluting one milliliter of the 10⁻² M TEP solution with nine milliliter of distilled water. Zero, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 ml volumes of the 10⁻³ M (10⁻⁶ moles of TEP) stock solution was pipetted into a 50 ml volumetric flask, and then diluted to volume with distilled water. Five milliliters of each diluted solution was mixed with 5 ml of 0.02 M thiobarbituric acid solution in each of the test tubes. These test tubes were placed in the dark to develop color for 15 h. The absorbance of the samples is measured by spectrophotometer at 532 nm.

A triangle test and a descriptive analysis by a trained panel were used in this study. The formal testing followed the modified procedures of Love (1988), St. Angelo et al. (1988), and Meilgaard et al. (1991). For evaluating oxidative flavor of beef and basic beef taste, panelists were screened with an odor of an acid solution and saltiness in a precooked roast beef by the triangle test. A six-member panel consisting of a faculty member, graduate students, and a visiting scholar from Department of Animal Sciences, The Ohio State University were utilized. Before formal testing, two training sessions of 1 h each were conducted to educate panelists on standard references and to develop the standardized attributes of precooked roast beef and intensity of attributes. The standard reference of roast beef flavor was fresh roasted beef that was refrigerated for less than 4 h. The standard reference of WOA (warmed-over aroma was observed by smelling) and WOF (warmed-over flavor was observed by tasting) was precooked roast beef after 4-d of refrigerated storage. The tenderness scores were standardized by agreement among panelists after comparing fresh cooked beef with a variety of tenderness. All standard references were reheated by a microwave at each test day. A 9-point category scale (Table 1) was utilized to discriminate the quantitative properties of precooked roast beef. A triangle test was used to evaluate difference of treatments at d 0, and the descriptive analysis was conducted at d 2 and 4. When the reheated samples reached an internal temperature of 60°C, they were presented to the panelist under standard evaluation condition (Meilgaard et al., 1991). The treatments were coded with 3-digit random numbers, placed on a warm plate, covered with aluminum foil and served to the panelists. Panelists evaluated samples in private booths under red light to eliminate color bias. Water and unsalted crackers were served to panelists and standard references (fresh roast beef, reheated roast beef and beef of different tenderness) were provided to panelists each evaluation day.

Total aerobic, psychrotrophic, and thermophilic bacteria tests were used to detect contamination of various bacteria in precooked roast beef which was not reheated after refrigerated storage on the day of test. Total aerobic plate count was evaluated using aerobic plate count agar (APC agar; Difco Laboratory, Detroit, Michigan, USA) at an incubation temperature of 25°C for 4 d (Speck, 1984). Psychrophilic bacteria were tested using APC agar at 4°C for 10 d. To get thermophilic counts, aliquots were plated on APC agar at 35°C for 48 h. The number of bacteria was converted to log₁₀ colony forming units per gram (log₁₀CFU/g).

A general linear model (GLM) was used to analyze the data by the Statistical Analysis System (SAS). Multiple comparisons of significant differences were determined by Duncan’s multiple range at α = 0.05.