Muscle fiber and color characteristics of different locations within beef Longissimus lumborum steaks
The objective of this study was to demonstrate the effect that muscle fiber composition differences within anatomical location of beef strip loin steaks elicit on color characteristics over a 7-d simulated retail display. Beef strip loins (n=120) were collected from a commercial abattoir and before aging, steaks were removed from the 13th rib for immunohistochemical analysis of muscle fiber cross-sectional area (CSA) and myosin-heavy chain (MHC) isoform distribution. Sampling locations included medial (MED), mid-lateral (M/L), and lateral (LAT) within each steak. After 14-d of aging, steaks were fabricated and L*, a*, surface metmyoglobin, and metmyoglobin reducing ability (MRA) were analyzed during a 7-d simulated retail display. There was a day×location interaction for all color characteristics (P<0.01). Initially, LAT was darker and redder than both MED and M/L (P<0.04), and M/L was redder (P<0.01) than MED. On d-7, MED tended to have reduced (P<0.05) L* value than the M/L and LAT area. The MED area was more (P<0.05) red than LAT, while M/L did not differ in redness compared to the other areas (P>0.10). On d-0, all three treatments differed in surface metmyoglobin percentage with the MED possessing greater a percentage than the other locations (P<0.01). At the end of display, all three treatments differed with the LAT possessing 0.83% and1.75% more metmyoglobin than M/L and MED, respectively (P=0.01). All locations had similar MRA on d 0 (P>0.10), but treatments differed in MRA on d-7 (P<0.05). The MED possessed 3.01% and 6.19% greater MRA than LAT and M/L, respectively (P<0.05). Percentage of type IIA fibers was not different between the three locations (P>0.10). The MED area tended to possess fewer type I fibers (P=0.10) than the M/L, and MED possessed less (P<0.01) type I fibers than LAT. Type I fiber number in LAT and M/L did not differ (P=0.25). The MED area had more (P=0.02) type IIX fibers than the M/L and LAT (P<0.02), but the M/L and LAT did not differ (P=0.94). The M/L area had larger type I and IIX fibers than MED and LAT (P<0.01), and MED tended to have larger (P=0.08) type I fibers than LAT. Also, LAT had smaller (P<0.01) IIA fibers than M/L and MED, but size of IIA fibers in M/L and MED were similar (P>0.10). Based on fiber distribution, expected biochemistry of these locations does not accurately explain color characteristics during simulated retail display.
Fiber type, color characteristics, sampling location