F Normal Fresh Red Meat Colors

Meat Preserving And Curing Guide

A Cured Meat Guide for Everyone

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(1) When fresh red meat is initially cut, the myoglobin (muscle pigment) color is a purplish red. See figure 2-2 for color changes.

Myoglobin (Purplish Red) Fresh-Cut Meat Color

Oxygenation Blooming Exposure to air

Oxymyoglobin (Bright Red) Desirable Retail Color

Oxidation ^ Dehydration

High Temperature

Metmyoglobin (Brown)

Stale Meat Color

^ Oxidation Off-Colored Meat Products

Figure 2-2. Fresh red meat color changes.

(2) On exposure to air, an oxygen molecule is added directly to the iron portion (oxygenation) of the myoglobin. This yields oxymyoglobin, which has a bright red color. This step is often called "blooming." This is the reason oxygen-permeable wrapping material is used with fresh meat. (Vacuum-packaged meat has a dark color when opened due to the blocking of this reaction (oxygenation).

(3) Upon exposure to oxygen, further oxidation takes place, and the iron in the oxymyoglobin is changed from a valence of +2 to a valence of +3 and this yields metmyoglobin, which is a brown pigment. Dehydration and high temperatures accelerate this reaction.

(4) Further oxidation of metmyoglobin yields off-colored meat, which is often green.

g. Normal Cured Red Meat Color. Cured red meat color depends on the reaction of nitric oxide (NO) with myoglobin to produce nitrosomyoglobin, which is a pinkish red pigment. To obtain NO, sodium or potassium nitrate/nitrite is added to the curing mixture. The nitrate is reduced to nitrite by bacterial reaction. The nitrite is converted to nitrous acid and finally to NO, which is a gas. Low pH, ascorbic acid, and other reducing conditions accelerate these reactions. The NO then reacts with myoglobin to produce nitrosomyoglobin. Nitrosomyoglobin may be oxidized to the undesirable brown pigment metmyoglobin. To block this reaction, cured meat is wrapped in oxygen-impermeable paper. Normally, after curing, heat is applied to the product during smoking. At this time, nitrosomyoglobin is converted to nitrosohemochrome. The globin portion of the pigment is fragmented and the cured meat takes on a bright purplish red color. See figure 2-3.

Myoglobin {Purplish Red) Fresh-Cut Meat Color

Nitric Oxide: Reducing Conditions

Nitrosomyoglobin (Pinkish Red) Cured Meat Color

Metmyoglobin (Brown) Stale Meat Color

4- Heat

Nitrosohemochrome (Bright Purplish Red)

Figure 2-3. Cured red meat color changes.

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