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Fragmentation Index of Raw Muscle as a Tenderness Predictor of Steaks from US Good and US Standard Steer and Bullock Carcasses

Tennessee Agricultural Experiment Station, University of Tennessee, Knoxville 37916

Abstract

Thirty steer (10 US Good, 20 US Standard) and 10 bullock carcasses (one US Good, nine US Standard) were selected from two commercial meat packing firms and aged for 10 to 14 days in a 2 C cooler. Each carcass was assigned scores for the various USDA quality and yield grade factors during a 48- to 120-hr post-mortem selection period. Steaks containing the longissimus muscle were obtained from the anterior end of the short loin and cooked to 70 C. They were then measured for tenderness with the Warner-Bratzler shear and evaluated by a trained eight-member sensory panel. Fragmentation index (FI) was determined on fresh and frozen raw longissimus muscle at each of three posthomogenization residue fraction drying periods (10 min, 40 min and 24 hr). Sarcomere length also was determined. Simple correlation coefficients relating FI (10 min, 40 min and 22 hr) to tenderness rating for bullocks were: (1) –.74, –.75 and –.72, respectively, for fresh muscle and (2) –.70, –.66 and –.69, respectively, for frozen muscle FI. Simultaneous consideration of carcass physical traits, sarcomere length and eight FI values accounted for 78.7 and 72.6% of the observed variation in shear force value and tenderness rating of steaks from the 30 US Good and US Standard steer carcasses. FI determined from fresh longissimus muscle accounted for 48.4 and 44.5% more of the variation in cooked meat tenderness than did carcass physical traits and sarcomere length. The best prediction equations for fragmentation of either fresh or frozen raw muscle accounted for over 53% of the observed variation in cooked meat shear force values; this degree of precision can be achieved in approximately 15 min of laboratory time. These data indicate that FI of raw muscle can be used for stratification of low grading bullock and steer carcasses according to tenderness level of cooked loin steaks.

¹ Formerly with the Univ. of Tennessee; presently affiliated with Meats and Muscle Biol. Sec. Dept. of Anim. Sci., Texas A&M Univ., College Station.

² Dept. of Food Technol. and Sci.