University of Nebraska Cooperative Extension MP 76-A

Summary

The fiber type composition of 38 muscles of the beef chuck and round was studied to facilitate optimal muscle use in value-added products. Select grade chucks and rounds (n=4 each) were used. Muscles containing greater than 40% b-red fiber numbers were classified as red; greater than 40% a-white were classified as white. All others were classified as intermediate. Nine of 12 round muscles were white, while chuck muscles were equally dispersed between red (10 of 26), intermediate (9 of 26), and white (7 of 26), indicating variation among muscles of the chuck, which may create differences in processing characteristics.

Introduction

There is a relationship between ultimate meat quality and muscle fiber type composition. Muscles with increased white (W) fibers have more connective tissue, less intramuscular fat, and are less tender than muscles with more -red (R) fibers. Not only do individual muscles differ in fiber type composition, but muscle fiber types within a specific muscle may be affected by breed, sex, time on feed and maturity.

Muscle fiber types have been reported for many of the larger muscles of the beef carcass. Little attention has been given to the smaller muscles that comprise the chuck and the round. With many of these muscles going to further processing, there is a need for a fiber type profile of these muscles. The objective of this study was to characterize the histochemical muscle fiber type of 23 muscles of the beef round and 26 muscles of the beef chuck to help in the application of muscles into valueadded products through the use of further processing.

Procedure

Select-grade chucks and rounds (n=4 each) were chosen representing two weight ranges (550-650 lbs, and 800-900 lbs) and two yield grades (yield grade 1 and 3). Twelve muscles of the beef round and 26 muscles of the beef chuck were fabricated and sampled. Muscle samples were frozen in liquid nitrogen within nine days post mortem and subsequently stored at -112^oF until histochemical analysis was performed. One cubic centimeter of frozen tissue was mounted on a cryostat chuck

One cubic centimeter of frozen tissue was mounted on a cryostat chuck in such a manner to set muscle fibers perpendicular to the cutting blade. The mounted cubes were allowed to equilibrate to -4.0^oF before being sliced to a thickness of 12 mm on a cryostat. The slices were mounted on slides and allowed to equilibrate to room temperature before being stained.

Muscle sections were stained according to a simultaneous staining technique, which included a stain for succinic dehydrogenase activity and a stain for acid-active adenosine triphosphatase activity after acid incubation. Cover slips were permanently mounted over the stained tissue to enable fiber classification.

Fibers were classified on the basis of stain reactions: -red fibers stained dark brown, -red fibers were clear in the middle and surrounded by a blue ring, and -white fibers were clear. Fiber numbers were calculated by examining a minimum of 500 muscle fibers from muscle bundles containing at least 50 fibers per bundle. Muscle fiber percentage was calculated by counting the total number of each fiber type, dividing by the total number of fibers counted, and multiplying the quotient by 100:

Fiber Number (%) =
Fiber Number (-red, -red, or -white) / Total Fiber Number * 100.

Muscles were classified as red, intermediate, or white on the basis of the average muscle fiber number (%). Muscles were classified as red if they had more than 40% -red fibers. White muscles had more than 40% -white fibers, and all other muscles were classified as intermediate muscles.

Fiber diameters were found by capturing photomicrographs with a black and white, monochrome camera mounted on a light microscope. A minimum of 50 diameters of each fiber type -red, -red, and -white) were measured with the help of computer software. Muscle fiber area was calculated from the fiber diameters: A = * (diameter/2)² . Percent area was calculated for each fiber type by first multiplying the average fiber type number by the average of the fiber area for a specific muscle, next, dividing by the total area, and finally, multiplying the quotient by 100:

%A = (Average Fiber Area * Average Fiber Number (%) / Total Area ) *100.

The analysis of variance included muscle and carcass weight group as main effects. Significant (P< .05) interactions were separated using contrasts to test for linearity.

Results

Tests of the interaction of carcass weight group and muscle and tests of the effect of carcass weight group on muscle fiber type characteristics were not significant for any of the characteristics studied (P> .05). The effect of muscle on fiber type characteristics was always significant (P<.002). Data were pooled by muscle, and means were calculated for fiber number (%), diameter, area and percentage area. Means are presented by muscle classification in Tables 1, 2, and 3.

Based on the literature, we anticipated fiber-type characteristics would be significantly influenced by carcass weight, although this is indirectly associated with an animal s ultimate size and age at slaughter. Because animals used in this experiment were all taken from animals of the same carcass maturity, it was thought that the ultimate size of the animals from the two different carcass weight groups would significantly influence the muscle fiber type profile. No significant differences were noted for the weight of the carcass; this likely can be attributed to small sample numbers per weight group (n=2).

There were nine of 12 muscles from the round that were classified white. The three muscles from the round that were not classified as white (Vastus medialis>, Vastus lateralis, and Sartorious) were all classified as intermediate. In contrast, muscles of the chuck were evenly dispersed between red (10 of 26), intermediate (9 of 26), and white (7 of 26).

An even distribution of muscle fiber type profiles found in muscles from the chuck would suggest a large variability in processing characteristics of muscles of the beef chuck. Conversely, muscles of the beef round may be considered similar, and may not contain as wide a variability in processing characteristics as muscles from the beef chuck.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Elbert C. Dickey, Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.

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