Page 253 - Natural Antioxidants, Applications in Foods of Animal Origin

232 Natural Antioxidants: Applications in Foods of Animal Origin
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Oxygenation
Reduced Myoglobin, Mbg Oxymyoglobin, Oxymbg
(purple) (red)
Deoxygenation

Reduction Oxidation
(electron gain) (electron loss)

FIGURE 6.20 The three main types of raw meat pigments are in equilibrium during storage.
The equilibrium shifts away from red meat pigments to brown meat pigments as the meat and
lipid oxidize. (Modified from American Meat Science Association, Meat Color Measurement
Guidelines. www.meatscience.org.)

Scientists depend on reflectance colorimetry methods for assessing
meat color because it relates well to consumer preferences. Two methods
for evaluating surface meat color frequently used are CIE L*a*b* colorim-
etry described earlier and diffuse reflectance spectroscopy. Both methods
relay on light reflectance; however, diffuse reflectance spectroscopy is more
discriminating because the method measures the intensity of light at specific
wavelengths for oxymyoglobin, myoglobin, and metmyoglobin (610, 473,
and 572nm wavelengths, respectively). Diffuse reflectance spectroscopy
(Mancini et al., 2003) describes the oxidative status of meat pigments and
indirectly the extent of lipid oxidation.
The colorimetric reflectance data in the Figures 6.21(a) and 6.21(b) show
how the distribution for the principle raw meat pigments changes during
storage.

Diffuse Reflectance Spectroscopy Colorimetry, 95% Lean Ground Beef
Minolta 3500d at T= 0 days at 36°F (2°C) -38°F (3°C)

OxyMbg, 61%

FIGURE 6.21(a) Distribution of fresh meat pigments favors the red oxymyoglobin
(OxyMbg) pigments.