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Variations in the Amount, Distribution and Texture of Intramuscular Fat within Muscles of the Beef Carcass¹

Meat Science Research Laboratory, A.R.S., U.S.D.A., Beltsville, Md. 20705 and Livestock Division, A.M.S., U.S.D.A., Washington, D. C. 20250

Abstract

Four hundred and eleven beef carcasses were selected according to variations in amount of marbling at the 12/13th rib interface, the following muscle cross-sections were evaluated following breaking of each carcass: complexus (CO), spinalis dorsi (SD) and longissimus (LD)—combined and longissimus (LD)-individually-at the fifth/sixth rib interface; and the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM)-combined at the loin/round interface. Each muscle cross-section was evaluated for marbling amount, marbling distribution, marbling texture, lean color and lean maturity. In almost all carcasses, the amount of marbling was lower in chucks and rounds than at the 12/13th rib. As the amount of marbling score at the 12/13th rib decreased, scores in the round and chuck also decreased. When primal cuts were graded by the present system rounds (present system-1 degree less) were in the same quality grade as the carcass 56.4% of the time; however, chucks (present system-1 degree more) were in the same quality grade as the carcass with only 37.5% precision.

The lean of the round muscles averaged slightly darker colored than the LD at the 12/13th rib at most marbling levels, and the lean of the LD, CO and SD-combined was darker than the LD at the 12/13th rib at all marbling levels. The results of this study indicate that the present system (1 degree less) is most suitable for rounds, whereas, chucks should be graded using the same marbling requirements as for the carcass.

¹ This research was a joint effort of the Meat Science Research Laboratory, A.R.S,, U.S.D.A., Beltsville, Md. and the Livestock Division, A.M.S., U.S.D.A., Washington, D.C.

² Present address: Meat Science Research Laboratory, A.R.S., U.S.D.A., Building 201, Beltsville, Md. 20705.

³ Present address: Livestock Division, A.M.S., U.S.D.A., Washington, D.C.

⁴ Present address: Statistical Services, A.M.S., U.S.D.A., Washington, D.C.