Intramuscular Variation in Fresh Ham Muscle Color

Abstract Text: This experiment was conducted to characterize a defect involving pale muscle tissue in the superficial, distal portion of ham muscles, causing two-toned appearance of cured ham products.  Biceps femoris muscles (n = 200), representing 3 production systems, were obtained from the ham-boning line of a large processor.  Instrumental color attributes (L*, a*, and b*) were determined on the medial and lateral surfaces of the muscle using a Hunter MiniScan colorimeter (25 mm port) before they were sliced (2.54-cm-thick) perpendicular to the long axis of the muscle.  Slices were numbered from the proximal end of the muscle so that slice numbers represented anatomical location.  Severity of the defect was greatest on the distal end of the muscle corresponding to slices 6 and 7 (of 9 slice locations).  The superficial (affected, lateral) portion of these slices was separated from the deep (unaffected, medial) portion.  Myoglobin concentration and muscle pH were determined on both portions.  The medial surface of the muscle had much lower (P < 0.05) L* (53.1 versus 63.4) and greater (P < 0.05) a* (23.2 versus 15.3) and b* (18.5 versus 15.4) values than the lateral surface.  Compared to the superficial portion, the deep portion of the muscle had greater (P < 0.05) muscle pH (5.68 versus 5.51) and myoglobin content (1.98 versus 0.86 mg/g).  Muscle pH and myoglobin content explained 20 and 7% of the variation in L* values of the deep portion of the muscle, respectively.  Conversely, myoglobin content and muscle pH explained 28 and 8% of the variation in L* values in the superficial portion of the muscle, respectively.  Similar relationships were seen with regard to a* values.  Five minimally affected and 5 severely affected muscles were sampled in the superficial (lateral) and deep (medial) portions for muscle fiber type determination.  Fiber type distribution did not differ (P > 0.05) between the deep and superficial portions of minimally affected muscles.  However, in severely affected muscles, the deep portion had increased (P < 0.05) proportion of red fibers, and concomitant decrease (P < 0.05) in white fibers relative to the superficial portion.  Muscle fiber areas were smaller (P < 0.05) in severely affected muscles, regardless of location.  These data indicate that the superficial (lateral) portion of the muscle is much lighter and less red in color, resulting from a lack of myoglobin content in this portion of the muscle associated with a shift in muscle fiber type.

Keywords: Color, Myoglobin, Fiber-type