What form of myoglobin causes meat to appear brown in color due to depletion of oxygen?

The form of myoglobin that causes meat to appear brown due to the depletion of oxygen is metmyoglobin. This refers to a state of myoglobin in which the iron is oxidized from ferrous (Fe²⁺) to ferric (Fe³⁺), resulting in a brownish color. When meat is exposed to oxygen, myoglobin can bind to oxygen to form oxymyoglobin, which gives the meat a bright red color. However, when oxygen levels drop or when myoglobin is not actively binding oxygen, it can convert to metmyoglobin, leading to the typical brown coloration seen in aged or stored meat.

Understanding the transition of myoglobin states is crucial for meat preservation and quality management. For instance, the development of metmyoglobin can be influenced by various factors, including storage conditions and exposure to air. This is why fresh meat is often expected to be red, while older or improperly stored meat may present a less appealing brown color, signaling potential spoilage or quality degradation.