New procedure for improving precision and accuracy of instrumental color measurements of beef

The surface layers of steaks from bovine M. semimembranosus were prepared to have deoxy- (DMb), oxy- (OMb) and metmyoglobin (MMb) states using either chemicals (CHEM) or oxygen partial pressure packaging (OPP). Ninety-six different meat surface areas were measured in reflectance mode (400–1100 nm) for each preparation method. Reflectance spectra were converted to absorbance (A) and then transformed by Kubelka–Munk transformation (K/S) and/or extended multiplicative scatter correction (EMSC). Transformed spectra of prepared pure states were used to make calibration models of MMb, DMb and OMb using either selected wavelengths (SW) or partial least square (PLS) regression. Finally, the predicted myoglobin states were normalized to ensure that no state was < 0 or > 1 and the sum of all states equal to 1. Multivariate calibrations (i.e. PLS) outperformed the univariate calibrations (i.e. SW). The OPP method of preparing pure states was clearly best for OMb while the CHEM method was best for preparing MMb on fresh meat surfaces. Both preparation methods needed improvement concerning DMb. The CHEM(K/S) SW and the OPP EMSC(A) PLS methods predicted MMb, DMb and OMb with root-mean-square errors of cross validation (RMSECV) equal to 0.08, 0.16 and 0.18 (range 0–1) and 0.04, 0.04 and 0.04 (range 0–1), respectively. This new reflectance protocol has potential for routine meat color measurements.