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Why Red Meat Turn Brown When Vacuum Sealed

Key Words:
myoglobin, maillard reaction, oxidation, carbon monoxide, metmyoglobin

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There are many reasons that meat can turn brown. Cooking meat at a high temperature browns meat because of the maillard reaction. As meat ages it turns brown from oxidation. The oxidation process is a result of the bound iron molecule in myoglobin going from the ferrous to ferric form. This produces what is called metmyoglobin. Metmyoglobin is the cause of the characteristic brown coloration of meat that occurs as it ages.

But interestingly meat can quickly turn brown in minutes when it is vacuum packed. Vacuum packers have become very popular recently. Vacuum sealers help preserve foods by taking out the oxygen thereby prevent oxidation from occurring.

But in the case of red meat there is a profound effect on the color ---

red grass fed beef fillet   red beef turn brown after  vacuum sealing
Grass fed unprocessed beef shown as bright red due to oxygenated hemoglobin in meat
A similar piece of unprocessed meat turns brown shortly after being vacuum sealed

Why is meat red to begin with?

Meat is red when the pigment myoglobin that is contained in blood is bound to oxygen. Myoglobin is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. When oxygen is released from myoglobin there is a change in spectral properties of the myoglobin molecule. The result is a brownish color. The images above show two pieces of grass fed meat that were unprocessed. One was left exposed to the air and the other was vacuumed packed prior to cooking using the sous vide method. The strong vacuum pulled out air and drew oxygen molecules off the surface of the meat. Removing the meat from the bag showed that only the surface level turned brown.

Is Carbon Monoxide added to some meats to keep them red?

Carbon monoxide binds hemoglobin in much the same way that oxygen does, only 200x stronger. In fact CO will displace oxygen from hemoglobin (or myoglobin) because it has such great affinity for hemoglobin. It is a known fact that carbon monoxide is used in processed meats to keep the meat red for long periods of time. Shown below it is interesting that under vacuum the meat remained red.

Why did this processed piece of red meat from the supermarket not turn brown when vacuum sealed ?

Carbon Monoxide in Meats

While carbon monoxide treated meat may not be harmful when fresh it can mislead the consumer who may not be able to smell the actual protein,. Adding carbon monoxide to meat will not only keep meat red while on the shelf but after it's spoiled.



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