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Current fabrication methods to remove the round from the sirloin typically entail cutting across muscles of the knuckle, leaving the Beef Round Knuckle (MANP #167) on the round and the Beef Loin Bottom Sirloin Butt, Ball Tip (NAMP #185B) on the loin. This has two consequences. First, the muscle nomenclature changes, depending on where the muscles are located after they are cut. Second, the value of the various muscle pieces is affected.
Part of this pricing differential may depend on the naming of the cut. While the knuckle is often labeled a sirloin tip at retail, it retains the beef round nomenclature – e.g., Beef Round, Sirloin Tip (following Uniform Retail Meat Identity Standards (URMIS) guidelines). This can be avoided if the knuckle is separated from the round before the round-loin break is made, thereby leaving the knuckle on the loin. Under this fabrication scenario, the knuckle can be named Beef Loin, Sirloin Tip at retail. To accomplish this, some packers drop the beef knuckle prior to the break, sometimes even while the muscle is in the pre-rigor state. An alternative is to cut a diamond cut round, which leaves the full knuckle on the round and essentially removes the ball tip from the loin.
The objectives of this project were:
There were 12 USDA Choice and 12 USDA Select carcasses chosen for this study. Alternating sides were pre-fabricated and maintained as a control. The pre-fabricated (HOT) treatment consisted of cuts on the hot carcass which followed the natural seams between the knuckle and the surrounding muscles. Skeletal attachments to the bones were not cut.
After 2 d of chilling, internal knuckle temperature was measured and whole knuckles (including the ball tip) were removed from the carcass. They were vacuum-packaged and aged for 7 d. On d 7, the knuckles were cut into 1-inch steaks. There were six steaks, from the proximal to the distal end. The proximal end corresponds to the ball tip and the distal end was near the location of the patella (kneecap). Steaks from the knuckle possess two primary muscles - the rectus femoris and the vastus lateralis. Measurements of color and Warner-Bratzler shear force (WBSF) were made in the posterior, middle, and anterior locations within a steak for the rectus femoris and within the posterior and anterior locations within a steak for the vastus lateralis. Taste panel sensory ratings were made on every other steak, disregarding locations within a steak (due to sample size requirements).
The steaks were allowed to bloom for 1 hr. Color (L*, a*, and b*) was measured with a Hunter Colorimeter, using the 10-degree standard observer and illuminant A, on each steak. Higher values for L* are indicative of lightness while higher values for a* indicated greater redness. Higher b* values indicated a more yellow, less blue color.
Steaks were then individually vacuum packaged and frozen until shear force or taste panel analyses were conducted on every other steak. Prior to cooking, steaks were thawed over night at 1 C. They were cooked to an internal temperature of 70 C on Farberware Open Hearth broilers - a table-top broiler with an open heat element. For shear force, cooked steaks were wrapped in plastic and allowed to cool to room temperature before removing 3 cores from each location (posterior, middle, and anterior for rectus femoris and posterior and anterior for the vastus lateralis). For the taste panels, a trained panel evaluated 1 x 1 x 1 cm cubes of meat for juiciness, tenderness, and amount of connective tissue using 8-point rating scales (where 1 was the least desirable and 8 was the most desirable). Off-flavor intensity was also scored on an 8-point scale, but here 1 represented no off-flavor and 8 was extreme off-flavor intensity.
Pre-fabricated knuckles were 0.45 F colder after 48 hr of chilling. This can be regarded as a favorable result because it indicates pre-fabrication can speed chilling to the internal portion of the knuckle. This would be expected to reduce purge. In fact, the purge in the vacuum-packages of pre-fabricated knuckles after 7 d of aging was 0.19% while the control knuckles had 0.39% purge (P < 0.005).
This project measured the tenderness of the beef knuckle from the sirloin end to the shank end. The tenderness of the middle of the knuckle is intermediate to the ends; the shank end is distinctly less tender and less desirable than the rest. In all cases, the rectus femoris (knuckle center) was desirable. There were far greater differences in tenderness and color from one end of the knuckle to the other than from the pre-fabrication treatment to the control, again implying that the fabrication treatment is feasible. Pre-fabrication of the beef knuckle offers some advantages in temperature and tenderness and should be considered as an alternative fabrication method for packers.