NIRS technique is based on two fundamental characteristics [23,24]: relative transparency of human tissue to light in the near-infrared region (700-1000 nm) and the oxygenation-dependent absorption of oxyhemoglobin and oxymyoglobin (HbO2,
MbO2) and deoxyhemoglobin and deoxymyoglobin (Hb, Mb).
The colour of meat is determined by the relative amount of three myoglobin derivatives; i) reduced myoglobin, deoxymyoglobin (Mb), which is the purple pigment of deep muscle and known from meat under vacuum, ii) oxygenated myoglobin, oxymyoglobin (
MbO2), which is bright cherry red and considered to signify fresh meat by the consumer, and iii) oxidised myoglobin, metmyoglobin (MetMb), which is grey-brown (Rosenvold and Anderson, 2003).