Animals

A heterogeneous group of purebred Brahman cull heifers (n = 21; ∼2.5 yr old), cull cows (n = 18; ∼4.5 yr old) and crossbred Brahman bulls (n = 17; Bos indicus × Bos taurus, unknown age) was subjected to finishing grazing conditions in a ranch located at the western Venezuelan savannahs. This ranch named Hato Los Valentones, was located in Apure State; 7°54′North of the equator and 43 m above sea level with an average temperature of 22 to 29°C and a distinct rainy season from May to October that featured an annual precipitation ranging from 1,000 to 1,800 mm. Selected heifers (averaging 340 kg live weight) and cows (averaging 410 kg live weight) came from a cow-calf operation next to this ranch owned by the same livestock company, which were culled and removed from the herd due to failure to reproduce during the mating season. Bulls with similar body condition but unknown management history (averaging 405 kg live weight) were purchased from various beef producers in the area for this research trial. All animals were treated against ecto- and endo-parasites and vaccinated against foot-and-mouth disease before entering the trial and finished on native grass pasture (Leersia hexandra, Hymenachne amplexicaulis, Paspulum plicatulum). During 120 d, animals were rotated among pastures approximately every 28 d, remaining in each pasture for 4 d. When heifers, cows, and bulls were slaughtered, they had reached an average live weight of 386.46 kg, 456.78 kg, and 465.53 kg, respectively.

Harvesting and carcass evaluation

The animals were transported approximately 524 km from the ranch to a slaughter facility nearby Barquisimeto City, Lara State, where they fasted for 12 h with access to water. After the lairage period, the animals were slaughtered following commercial Venezuelan standard procedures (COVENIN, 1983).

After being chilled for 24 h at 2°C, carcasses were ribbed and evaluated according to the Venezuelan quality grading system (Decreto Presidencial No. 1896, 1997) and the USDA system (USDA, 2016). The current Venezuelan carcass grading system mandates a sex classification of cattle (steers, bulls, young bulls, heifers, and cows) and 2 optional grading systems: 1 by quality and 1 by yield. Individual carcass grading data were collected by 3 meat scientists, faculty members of the Universidad del Zulia. Prior to the trial, a carcass grading training program was conducted in multiple facilities by an experienced meat evaluation trainer of the USDA Agricultural Marketing Service as was previously described in a paper by Huerta-Leidenz (2010).

Both quality- and yield-related traits can be described as follows: (1) leg muscle profile (muscle development of round and rump), where: 1 = very convex; 2 = convex; 3 = straight; 4 = concave; or 5 = very concave; (2) carcass finish (amount and distribution of subcutaneous fat), where: 1 = very abundant; 2 = abundant; 3 = moderate; 4 = slight; or 5 = devoid; (3) back fat thickness (minimum back fat thickness on the loin, assessed at the 12th through 13th rib interface); (4) ribeye area (REA; assessed at the 12th through 13th rib interface), and (5) adipose fat maturity (color of subcutaneous fat), where: 1 = ivory white; 2 = creamy white; 3 = yellowish; 4 = yellow; or 5 = orange. Both quality grading systems were similar in how they evaluated skeletal (bone characteristics and backbone cartilage ossification; 100 = A [younger maturity]; 400 = D [older maturity] and degrees 0 to 99), and lean maturities (color and texture of ribeye muscle; where 100 = A [younger maturity]; 400 = D [older maturity]; and degrees 0 to 99) as well as marbling scores (amount and distribution of intramuscular fat; where: 100 = practically devoid; 200 = traces; 300 = slight; and degrees 0 to 99) were evaluated. Based on the evaluation of the skeletal, lean and adipose maturities, marbling and amount and distribution of subcutaneous fat; heifer carcasses were assigned A or B quality grades, all bull carcasses were graded as B and cow carcasses were graded as C.

Carcass cutability

At 48 h post-mortem, the cold carcass weight was recorded and the left side was fabricated into commercial wholesale cuts. During fabrication, the exterior fat was trimmed off to a maximum thickness of 6.4 mm on the cut surfaces. It is noteworthy that some modifications to the official cut description (COVENIN, 1982) resulted from the packing plant fabrication practices. In this regard, the neck and chuck comprised a single sub-primal (referred as chuck roll), as well as the ribeye and striploin which were boned out as a whole sub-primal (named as “loins”), and the brisket (cutting on the proximal portion of the ribs near of the costal-vertebrae joints and not at half of the ribs; Huerta-Leidenz et al., 2016). A detailed anatomical description of typical, commercial processes of beef carcass fabrication in Venezuela has been reported by Montero et al. (2014) and international equivalences in cut nomenclature were published by Huerta-Leidenz (2013). Accordingly, Table 1 depicts the myology composition of main Venezuelan beef cuts, and the United States equivalents. The United States nomenclature was used to identify sub-primal beef cuts throughout the manuscript.

After completion of the fabrication process, individual weights of boneless and bone-in cuts were recorded. Thereafter, the trimmed (clean) bone and excess fat components of the bone-in cuts were removed and all resulting co-products (fat trimmings and bone) were weighted again. The total yield of product (i.e., individual subprimal cuts or total amount of lean edible meat) and co-product components were computed as proportions (%) of the cold carcass. For generating variables of significance in the domestic meat trade, products with similar market value were classified into 4 value-based, composite groups (Montero et al., 2014) as follows: (1) High-value boneless cuts [HVC; including tenderloin, “loins”, top sirloin cap, center cut sirloin, eye of round, inside round, outside round, knuckle, and tri-tip, (2) Medium-value boneless cuts (MVC; including chuck tender, chuck roll, top blade, and heel of round), (3) Total valuable cuts (TVC; the sum of the high- and medium-value cuts), (4) Low-value cuts [LVC; including bone-in cuts from the forequarter and hindquarter (fore shank and hind shank, brisket, rib plate = short ribs + back ribs + chuck short ribs) plus the skirts (inside skirt, flank, flank steak, rose meat and shoulder rose, outside skirt and hanging tender)].

Procurement of samples for shear force and sensory evaluation

At 48 h post-mortem, two 2.54-cm thick ribeye roll steaks from the right carcass side were sequentially removed from the boneless ribeye starting from the rib-loin interface toward the cranial portion of the longissimus thoracis muscle (LDT) and vacuum-packaged for the Warner-Bratzler shear force (WBSF) determination and sensory analyses. The ribeye steaks were randomly chosen, alternating anatomical position for shear force and sensory panel traits. Steaks were not subjected to any intentional aging process because, in Venezuela, most of the beef carcasses and/or sub-primals are marketed within 2 to 7 d post-mortem without applying wet or dry aging, electrical stimulation or any other technology to improve their quality (Rodas-González et al., 2009). Therefore, all vacuum-packaged ribeye steaks were immediately frozen at –30°C and kept at –20°C until further sensorial and WBSF evaluations.

Cooking procedure

Steaks were tempered in a refrigerator at 4°C for 24 h prior to shear force or sensory evaluation. Sample preparation and cooking procedures were followed according to guidelines described by the American Meat Science Association (American Meat Science Association, 2016). Before cooking, thawed weights were recorded. The steaks were cooked in an open electric Oster indoor grill (Sunbeam Products, Inc., model 4777–33, Boca Raton, FL), which was preheated (approximately at 165°C). Steaks were turned once during broiling (at 35°C) and removed from the grill when they reached an internal temperature of 70°C. Once steaks exited the grill, final internal temperature, cooked time and cooked weight were recorded immediately. Cooking loss (%) was calculated using the following formula: [(thawed weight, g – cooked weight, g) / thawed weight, g] × 100.

Shear force determinations

After steaks were cooked, they were allowed to cool down at room temperature. Between 6 and 10 core samples (1.27 cm in diameter), depending on the cross-sectional area within the LDT muscle, were removed parallel to the muscle fiber orientation taking care not to include large areas of fat or connective tissue in each core. Each core was sheared once using a Warner-Bratzler shear machine (G-R Elec. Mfg. Co, Manhattan, KS). The WBSF values were recorded in kg, and the values from the 6 to 10 cores of 2 steaks were averaged for statistical analysis.

Sensory tests with the descriptive trained panel

Steaks for sensory analysis were cooked as described above (American Meat Science Association, 2016). Cooked steaks were trimmed of visible fat and connective tissues. Each steak was cut into 8 to 15 cubed samples (≈1.27 cm³ of size) of LDT muscle. Cubed samples from each experimental unit were placed on pre-coded discardable, cardboard plates and stored in a preheated oven (at 50°C) for 7 min prior serving to panelists. Cubed samples were served warm, unsalted and unspiced, accompanied with a glass of water that was used to rinse the mouth after tasting each sample.

The trained sensory panel was composed of 6 to 8 trained judges. A detailed description of the panelists’ selection and training was reported by Jerez-Timaure et al. (1994) and Huerta-Leidenz et al. (1996). Two cubed samples taken from steaks of each animal were served warm to each judge. Sixteen samples were served in 2 sessions (8 samples per session) in 1 d and 1-hour break between sessions. All samples were evaluated during 2 d for the trained panelists, and samples were served to the panel, balancing graded sex classes. Judges scored the samples for juiciness, muscle fiber tenderness, overall tenderness, amount of connective tissue, and flavor intensity using an 8-point structured rating scale for each attribute (where 1 = extremely dry, extremely tough, extremely tough, an abundant amount of connective tissue, extremely bland, respectively, and 8 = extremely juicy, extremely tender, extremely tender, no connective tissue, extremely intense, respectively; American Meat Science Association, 2016). The values from 6 to 8 trained judges per animal were averaged for statistical analysis.

Statistical analyses

Data were analyzed as a completely randomized design using the MIXED model procedures of SAS (SAS Inst. Inc., Cary, NC) version 9.4 with the sex class plus quality grade combined in a single independent variable. Accordingly, the following combinations were considered as the 4 levels of the class-grade main effect: A-graded heifer, B-graded heifer, B-graded bull and C-graded cow.

Carcass within treatment was used as the random effect. Least squares means for unequal subclass number were separated (F test, P < 0.05) using least significant differences generated through the PDIFF option of SAS. The degrees of freedom in the denominator were adjusted using the Satterthwaite procedure.

Additionally, chi-square analysis (Fisher’s exact test) was used to test differences among frequencies for class-grade to describe the proportion of tender steaks [WBSF value ≤ 40.13N (4.09 kg)] using threshold values for tenderness classes described by Rodas-González et al. (2009).