Tenderness and Electrical Impedance of Ribeye Steaks from Steers Finished on Forage

Linda Benedict, McMillin, Kenneth W., Persica III, Manuel Anthony, Gregorie, Cole  |  11/17/2014 9:37:47 PM

A bioelectrical impedance analyzer was used to measure electrical properties in ribeye steaks from steers finished on three forage systems. Photo by Kenneth W. McMillin

Kenneth W. McMillin, Manuel A. Persica III, J. Cole Gregorie and James N. Maynard

The study of meat allows for the identification of animals, production systems or processing techniques that result in desired properties. Among the desired attributes of meat, tenderness is the most important palatability trait to consumers. Estimates of tenderness in laboratory settings have used Warner- Bratzler (W-B) shear force techniques to provide an objective measure of the amount of force required to cut through cooked meat samples. A more recent development for tenderness determination is the use of slice shear force, which measures the force through a larger sample of the cooked meat. Both techniques require cooking the sample and measuring the shear force required to cut through the cooked sample.

Various methods of estimating or predicting tenderness of cooked meat based on raw meat properties have been investigated. Several studies have linked electrical values of meat to tenderness, flavor, freshness and other properties, but results vary because myofibrillar proteins that degrade and connective tissue that does not degrade have varying electrical values. One study suggested electrical impedance as the most effective means of identifying cattle carcasses that would produce tender beef. Electrical impedance is a measure of alternating electrical current that has two components or vectors – resistance and reactance – and indicates the capability of a material to oppose the flow of electric current.

The objective of this study was to measure surface electrical impedance, resistance, reactance and phase distributed generation on raw beef steaks and compare them with the W-B shear force and slice shear force of cooked beef steaks from steers finished on three different forage systems in three consecutive years. The forage systems were:

System 1 was primarily bermudagrass during summer, fall and spring and ryegrass in winter.

System 2 was bermudagrass in summer, a dallisgrass-and-clovers mix during fall and spring, and a ryegrass- clovers mix during winter.

System 3 was bermudagrass and sorghum- sudangrass hybrid with forage soybeans during summer, a dallisgrass- clovers mix during fall and spring, and a ryegrass-clovers mix during winter.

Each year, six steers randomly selected from each of the three forage systems were humanely slaughtered in a Louisiana state-inspected meat plant. Carcasses were chilled in a 36-degree cooler overnight, and primal rib cuts were removed from each carcass side. A 9-to-11-rib section from one side was divided into Longissimus dorsi – ribeye muscle – other lean tissue, fat and bone while the remaining portion of that rib primal cut was cut into 1-inch-thick steaks for determination of cook yield, shear force tenderness and electrical conductivity.

Each steak was vacuum packaged, labeled and stored for seven days at 37 degrees before measuring electrical resistance, reactance, phase distributed generation and impedance with a bioelectrical impedance analyzer. After measuring electrical parameters, the steaks were weighed and then cooked on an open hearth grill to 158-degree internal temperature. After the steaks were cooled to room temperature and weighed, half-inch cores were removed for measuring W-B shear force, and 1-inch slices were removed for measuring slice shear force. Cook yields were calculated as the difference between initial weight and cooked weight.

Data were analyzed to compare differences among years, forage systems and steer groups and to determine correlations among shear and electrical variables.

Cook yield of steaks did not differ by year or forage system and ranged from 72.9 percent to 78 percent on steaks used for W-B shear and 72 percent to 79.5 percent on steaks used for slice shear force determination. There also were no differences due to year or forage system on shear forces of steaks with the W-B method or the slice shear method. Slice shear required higher force than the force to shear smaller samples with the W-B shear method, which was expected because of the larger thickness of the sample used for slice shearing. All steak samples using the W-B method were below the maximum shear force values to be labeled as “tender” under the USDA Agricultural Marketing Service certification standard, and steaks from the first two years would meet the “very tender” standard. Most steaks measured using slice shear force exceeded the maximum value for the “tender” labeling.

The reactance and phase distributed generation of steaks did not differ by year or forage system. The resistance and impedance electrical measurements were highest on steaks from the third year and lowest on steaks from the first year, but there were no differences in the electrical measurements of steaks from cattle finished on the three forage systems within each year.

The cook yields of steaks used for W-B shear and slice shear were not related. The cook yield of W-B steaks was highly negatively correlated with the W-B shear, which suggests the retention of fluids during cooking resulted in a lower force needed to shear the samples. The W-B shear force was highly related to the slice shear force, which was expected because both methods are used as objective measures of meat tenderness.

Impedance was the only electrical measurement moderately related to W-B shear force. Electrical resistance was highly related to reactance, and impedance was highly related to all three of the other electrical measurements. These results were expected because impedance is a function of resistance and reactance.

The year or type of forage system had no influence on cooking yields or objective shear force values of ribeye steaks from the three years and three forage systems. This study indicates the forage system did not influence the important palatability property of tenderness. Additional testing with more and diverse beef samples is needed to more adequately determine the relationships among electrical measurements on raw steaks with cooked beef palatability properties.

Kenneth W. McMillin holds the Mr. & Mrs. Herman E. McFatter Endowed Professorship in Animal Science. His co-authors are Manuel A. Persica III, research associate in the School of Animal Sciences; J. Cole Gregorie, research associate at the Sweet Potato Research Station in Chase; and James N. Maynard, graduate assistant in the School of Animal Sciences.

This article was published in the fall issue of Louisiana Agriculture

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