Variations in meat colour due to factors other than myoglobin chemistry; a synthesis of recent findings (invited review)

This review focuses on the mechanisms responsible for some the achromatic aspects of meat colour (paleness or darkness) due to light scatter from structures within the tissue. Recent investigations have highlighted the role of three key mechanisms contributing to variations in the lightness of meat: (1) Variations in the myofilament lattice spacing, and the resultant changes in myofibril diameter and muscle fibre diameter. A 20% increase in lightness (L* value) between muscles with ultimate pH of 6.1 versus 5.4 is accompanied by a 17% change in muscle fibre diameter. (2) Variations in sarcomere length, if these are associated with changes in myofilament and myofiber diameter, (3) Variations in sarcoplasmic protein distribution, including whether these are bound or precipitated onto the myofilaments, as demonstrated by an increase of 1.24 in the ratio of X-ray diffraction intensities from mass centered on the thin filaments versus thick filaments in dark (pH 6.15) versus light (pH 5.47) muscles. For clarity, the discussion of these mechanisms is principally in relation to pH and temperature at rigor (5 degrees C-35 degrees C), although the possibility of contributions from numerous other factors is acknowledged.