Research and Reviews: Meat 2001

Special Circular 183-02

Effects of Electrical Stimulation on Lipid Oxidation, Warmed-over Flavor, and Quality of Roast Beef

Materials and Methods

Sample preparation

Stimulated meat was provided by The Ohio State University Meat Lab. A low voltage (40 volts) was used to stimulate the carcass. The electrodes of the stimulator were placed in the round and at the atlas on the neck. Stimulation sequence was 2.5 seconds on and 1.5 seconds off. The total stimulation time was 3 minutes. The beef round primal cuts were deboned and trimmed of visible fat and connective tissue after stimulation. All beef round primal cuts were cut into uniform cubes of roasts (8 x 8 x 8 cm dimension). The muscles were roasted in a hot-air convection oven (Type EFIII, The GS Blodgett Co Inc., Burlington, VT) at 350^oF (168^oC) until the internal temperature (I.T.) of the roasts reached 160oF (71^oC). After roasting the meat products were chilled in a cooler (Model 7030 S/N 75368, Forma Scientific, Division of Mallinckrodt, Inc., OH) until the temperature of the products was 40^oF (4^oC). These meat products were separately placed into unsealed plastic bags for refrigerated storage (40^oF) until being tested. Samples were reheated in a microwave (Model M312, 2450 Hz, Hobart Corp., Troy, OH) to an I.T. of 140^oF (60^oC) before doing all measurements, except for the microbiological test that was preformed on non-reheated tissue.

Measurements

Moisture content (Oven Dry Method; Ockerman, 1985) was measured in a drying oven at 100^oC for 18 hours. A Corning pH meter (Model 7) measured the pH values of the samples. The pH meter was standardized by a buffer solution (pH 7.00 at 25^oC) before testing. Ten grams of sample was weighed and blended with 100 ml of distilled water in a polyethylene sterile bag by the Stomacher Lad Blender 400 for 1 minute (Ockerman, 1985). The crude fat (ether extraction method for 8 hrs) followed the technique described by Ockerman (1985). A modified extraction of the TBARS method was analyzed for lipid oxidation (Pensel, 1990).

The results of electrical stimulation were evaluated by yields, tenderness by Warner-Bratzler using a 2.54 cm (1-in) core, and sensory test. The shear values of cooked roast beef were evaluated by the Warner-Bratzler (G.K. Electric Mfg. Co., Kansas) instrument (Ockerman, 1985). The following formula was used to calculate the yields of the treatments:

Yield = final cooked product weight/fresh meat weight.

A triangle test and a descriptive analysis by trained panels were used in this study. The training session and 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 of precooked roast beef by the triangle test. A six-member panel consisting of faculty, graduate students, and a visiting scholar was from The Department of Animal Sciences at The Ohio State University. Before formal testing, two training sessions of 1 hour 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 hours. The standard reference of WOF and warmed over aroma (WOA) was precooked roast beef after 4-days of refrigerated storage. The tenderness was standardized by discussion of panelists with fresh cooked beef. A microwave rewarmed all standard references. A 9-point category scale (Table 1) was utilized to discriminate the quantitative properties of precooked roast beef. The triangle test was used to evaluate difference of treatments at day 0, and the descriptive analysis was conducted at day 2 and 4. When the reheated samples reached an internal temperature of 140^oF (60^oC), 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 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 were provided to panelists each evaluation day.

Total aerobic, psychrothrophic, and thermophilic bacteria tests were utilized to detect contamination of various bacteria in precooked roast beef. Total aerobic plate count is a test for mesophile growing at room temperature; however, the psychrothrophic bacteria count was used to detect the number of psychrothrophiles able to grow in refrigerated storage. The survival of thermophile after roasting was examined by thermophilic bacteria count (Yetim et al., 1996). Total aerobic plate count was evaluated using aerobic plate count (APC; Difco Laboratory, Detroit, MI) agar at an incubation temperature of 25^oC for 4 days (Speck, 1984). Psychrothrophile was tested using APC agar at 7^oC for 7 days and also thermophile was incubated with APC agar at 35^oC for 48 hours. All microbiological tests were conducted on day 7 of refrigerated storage due to less than twenty count/g of all treatments after roasting (160^oF) until 7 days and this was determined from pretest data (not shown). The number of bacteria was converted to log₁₀ colony forming units per gram (log₁₀CFU/g).