Page 252 - Natural Antioxidants, Applications in Foods of Animal Origin

Methods and Their Applications for Measuring 231
VetBooks.ir The interrelationship between meat color and lipid oxidation (Greene,

1969) places importance on CIE (International Commission on Illumina-
tion), L*a*b* reflectance colorimetry as well as diffuse reflectance spectros-
copy is an important consideration when evaluating the oxidative stability in
value-added raw meat products.
Reflectance spectroscopy requires a light source, an object (meat
surface), and a sensor. In this case, the colorimeter describes raw meat color
in terms of L* (lightness and darkness), a* (redness), and b* (yellowness).
Fresh meat has initial high a* values (redness) (Table 6.5).

TABLE 6.5 Reflectance Spectroscopy is Used to Monitor the Raw Meat Color Stability
During Storage. Raw Meat Color and Lipid Oxidation in Raw Meats are Interrelated, as Meat
Color Changes from Red (Relatively High a*/b* in Combination with Higher L* Values)
to Brown (Relatively Low a*/b* in Combination with Low L* Values) Lipid Oxidation
Increases. Data from Internal Fresh Beef Storage Stability Study.

CIE L*a*b* reflectance colorimetry
Sample description L* a* b* a*/b* C* Hue angle a* × b*
Fresh meat color (red) 57.42 24.40 13.48 1.81 27.88 28.93 328.91
Oxidized meat color 52.94 12.76 7.51 1.70 14.81 30.49 95.83
(redish brown)

FIGURE 6.19(b) Reflectance colorimetry has three main components, a light source, an
object (i.e. meat surface) and a sensor. The sensor detects changes in redness (a*, a* ÷ b*
+
or a* ÷ b*), color saturation C* chroma= = (a* b* , hue angle or color (in the CIE color
2
sphere. For diffuse reflectance spectroscopy the intensity of light at a particular wavelength is
detected (Modified from Hunt, M.; King, A. Meat Color Guideline Measurements; American
Meat Science Association: Savoy, Illinois, 2012.)
The color of meat is based on the relative concentrations of oxymyo-
globin (red), myoglobin (purple), and metmyoglobin (brown) (Fig. 6.20).
For raw packaged meats (e.g., ground beef, pork, turkey) higher levels of
oxymyoglobin are associated with freshness and quality. Meat containing
higher levels of metmyoglobin is associated with oxidized or rancid flavors.