2.2. Meat colour and metmyoglobin analysis
Meat colour was measured at the surface of lamb steaks using a reflectance spectrophotometer (Minolta CM-2002; Osaka, Japan) 30 min after pack opening, in order to allow colour stabilisation on air exposure. CIE L∗ (lightness), a∗ (redness) and b∗ (yellowness) parameters were recorded (CIE, 1978). The average value for each steak was the mean of 10 determinations.
The metmyoglobin (MetMb) percentage of the total myoglobin perceptable at the steak surface was estimated spectrophotometrically, according to Stewart, Zipser, and Watts (1965), by measuring steak surface reflectance at 525 and 572 nm (Minolta CM-2002; Osaka, Japan). The maximum value of the ratios of (K/S)572 to (K/S)525 at the beginning of the experiment was fixed as 0% metmyoglobin; K and S were the absorption and the scattering coefficients, respectively, and K/S ratios were calculated from reflectivity (R∞) values using the Kubelka–Munk equation. The value of 100% MetMb was obtained following the same procedure after oxidising a sample in a 1% (w/v) solution of potassium ferricyanide (Ledward, 1970). The average value for each steak was the mean of 10 determinations.